qnx4: fix to avoid panic due to buffer overflow

  qnx4 dir name length can vary to be of maximum size
QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
'link info' entry is stored and the status byte is set.
So to avoid buffer overflow check di_fname length
fetched from (struct qnx4_inode_entry *)
before use in strlen to avoid buffer overflow.

panic context
[ 4849.636861] detected buffer overflow in strlen
[ 4849.636897] ------------[ cut here ]------------
[ 4849.636902] kernel BUG at lib/string.c:1165!
[ 4849.636917] invalid opcode: 0000 [#2] SMP PTI
..
[ 4849.637047] Call Trace:
[ 4849.637053]  <TASK>
[ 4849.637059]  ? show_trace_log_lvl+0x1d6/0x2ea
[ 4849.637075]  ? show_trace_log_lvl+0x1d6/0x2ea
[ 4849.637095]  ? qnx4_find_entry.cold+0xc/0x18 [qnx4]
[ 4849.637111]  ? show_regs.part.0+0x23/0x29
[ 4849.637123]  ? __die_body.cold+0x8/0xd
[ 4849.637135]  ? __die+0x2b/0x37
[ 4849.637147]  ? die+0x30/0x60
[ 4849.637161]  ? do_trap+0xbe/0x100
[ 4849.637171]  ? do_error_trap+0x6f/0xb0
[ 4849.637180]  ? fortify_panic+0x13/0x15
[ 4849.637192]  ? exc_invalid_op+0x53/0x70
[ 4849.637203]  ? fortify_panic+0x13/0x15
[ 4849.637215]  ? asm_exc_invalid_op+0x1b/0x20
[ 4849.637228]  ? fortify_panic+0x13/0x15
[ 4849.637240]  ? fortify_panic+0x13/0x15
[ 4849.637251]  qnx4_find_entry.cold+0xc/0x18 [qnx4]
[ 4849.637264]  qnx4_lookup+0x3c/0xa0 [qnx4]
[ 4849.637275]  __lookup_slow+0x85/0x150
[ 4849.637291]  walk_component+0x145/0x1c0
[ 4849.637304]  ? path_init+0x2c0/0x3f0
[ 4849.637316]  path_lookupat+0x6e/0x1c0
[ 4849.637330]  filename_lookup+0xcf/0x1d0
[ 4849.637341]  ? __check_object_size+0x1d/0x30
[ 4849.637354]  ? strncpy_from_user+0x44/0x150
[ 4849.637365]  ? getname_flags.part.0+0x4c/0x1b0
[ 4849.637375]  user_path_at_empty+0x3f/0x60
[ 4849.637383]  vfs_statx+0x7a/0x130
[ 4849.637393]  do_statx+0x45/0x80
..

Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
---
 fs/qnx4/namei.c | 7 +++++++
 1 file changed, 7 insertions(+)
  

On 2023-11-12 10:53 Ronald Monthero wrote:
> qnx4 dir name length can vary to be of maximum size
> QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> 'link info' entry is stored and the status byte is set.
> So to avoid buffer overflow check di_fname length
> fetched from (struct qnx4_inode_entry *)
> before use in strlen to avoid buffer overflow.

[snip]

> 
> Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> ---
>  fs/qnx4/namei.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..825b891a52b3 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
>  	} else {
>  		namelen = QNX4_SHORT_NAME_MAX;
>  	}
> +
> +	/** qnx4 dir name length can vary, check the di_fname
> +	 * fetched from (struct qnx4_inode_entry *) before use in
> +	 * strlen to avoid panic due to buffer overflow"
> +	 */
> +	if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> +		return -ENAMETOOLONG;

sizeof(de->di_fname) equals QNX4_SHORT_NAME_MAX, so this test fails as soon as 
a filename is longer than that!

This quick fix (untested!) should do the trick (and avoids computing the length 
of the name twice):

diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..7694f86fbb2e 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -40,9 +40,7 @@ static int qnx4_match(int len, const char *name,
 	} else {
 		namelen = QNX4_SHORT_NAME_MAX;
 	}
-	thislen = strlen( de->di_fname );
-	if ( thislen > namelen )
-		thislen = namelen;
+	thislen = strnlen(de->di_fname, namelen);
 	if (len != thislen) {
 		return 0;
 	}

Cheers
Anders
  

On Mon, Nov 13, 2023 at 2:16 AM Anders Larsen <al@alarsen.net> wrote:
>
> On 2023-11-12 10:53 Ronald Monthero wrote:
> > qnx4 dir name length can vary to be of maximum size
> > QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> > 'link info' entry is stored and the status byte is set.
> > So to avoid buffer overflow check di_fname length
> > fetched from (struct qnx4_inode_entry *)
> > before use in strlen to avoid buffer overflow.
>
> [snip]
>
> >
> > Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> > ---
> >  fs/qnx4/namei.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > index 8d72221735d7..825b891a52b3 100644
> > --- a/fs/qnx4/namei.c
> > +++ b/fs/qnx4/namei.c
> > @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
> >       } else {
> >               namelen = QNX4_SHORT_NAME_MAX;
> >       }
> > +
> > +     /** qnx4 dir name length can vary, check the di_fname
> > +      * fetched from (struct qnx4_inode_entry *) before use in
> > +      * strlen to avoid panic due to buffer overflow"
> > +      */
> > +     if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> > +             return -ENAMETOOLONG;
>
> sizeof(de->di_fname) equals QNX4_SHORT_NAME_MAX, so this test fails as soon as
> a filename is longer than that!

I suppose de->di_fname can be QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX isn't it ?
It's set based on di_status, if di_status is set, then it will be
QNX4_NAME_MAX and otherwise QNX4_SHORT_NAME_MAX.
We capture that into namelen, prior to the  string length check  - if
(strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
as below:

        de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
        *offset += QNX4_DIR_ENTRY_SIZE;
        if ((de->di_status & QNX4_FILE_LINK) != 0) {
                namelen = QNX4_NAME_MAX;
        } else {
                namelen = QNX4_SHORT_NAME_MAX;
        }

BR,
Ron


> This quick fix (untested!) should do the trick (and avoids computing the length
> of the name twice):
>
> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..7694f86fbb2e 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -40,9 +40,7 @@ static int qnx4_match(int len, const char *name,
>         } else {
>                 namelen = QNX4_SHORT_NAME_MAX;
>         }
> -       thislen = strlen( de->di_fname );
> -       if ( thislen > namelen )
> -               thislen = namelen;
> +       thislen = strnlen(de->di_fname, namelen);
>         if (len != thislen) {
>                 return 0;
>         }
>
> Cheers
> Anders
>
>
  

On 2023-11-13 10:25 Ronald Monthero wrote:
> On Mon, Nov 13, 2023 at 2:16 AM Anders Larsen <al@alarsen.net> wrote:
> > On 2023-11-12 10:53 Ronald Monthero wrote:
> > > qnx4 dir name length can vary to be of maximum size
> > > QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> > > 'link info' entry is stored and the status byte is set.
> > > So to avoid buffer overflow check di_fname length
> > > fetched from (struct qnx4_inode_entry *)
> > > before use in strlen to avoid buffer overflow.
> > 
> > [snip]
> > 
> > > Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> > > ---
> > > 
> > >  fs/qnx4/namei.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > > index 8d72221735d7..825b891a52b3 100644
> > > --- a/fs/qnx4/namei.c
> > > +++ b/fs/qnx4/namei.c
> > > @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
> > > 
> > >       } else {
> > >       
> > >               namelen = QNX4_SHORT_NAME_MAX;
> > >       
> > >       }
> > > 
> > > +
> > > +     /** qnx4 dir name length can vary, check the di_fname
> > > +      * fetched from (struct qnx4_inode_entry *) before use in
> > > +      * strlen to avoid panic due to buffer overflow"
> > > +      */
> > > +     if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> > > +             return -ENAMETOOLONG;
> > 
> > sizeof(de->di_fname) equals QNX4_SHORT_NAME_MAX, so this test fails as
> > soon as a filename is longer than that!
> 
> I suppose de->di_fname can be QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX isn't it
> ? It's set based on di_status, if di_status is set, then it will be
> QNX4_NAME_MAX and otherwise QNX4_SHORT_NAME_MAX.
> We capture that into namelen, prior to the  string length check  - if
> (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> as below:
> 
>         de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
>         *offset += QNX4_DIR_ENTRY_SIZE;
>         if ((de->di_status & QNX4_FILE_LINK) != 0) {
>                 namelen = QNX4_NAME_MAX;
>         } else {
>                 namelen = QNX4_SHORT_NAME_MAX;
>         }
> 
> BR,
> Ron

sizeof(de->di_fname) is evaluated as QNX4_SHORT_NAME_MAX already at compile 
time, see the definition of di_fname in uapi/linux/qnx4_fs.h

I agree that the code is confusing, as 'de' is declared as a pointer to a 
struct qnx4_inode_entry but in reality points to a struct qnx4_link_info iff 
QNX4_FILE_LINK is set in de->di_status.
(Note that the corresponding field dl_status in qnx4_link_info is at the same 
offset as di_status in qnx4_inode_entry - that's the disk layout.)

> > This quick fix (untested!) should do the trick (and avoids computing the
> > length of the name twice):
> > 
> > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > index 8d72221735d7..7694f86fbb2e 100644
> > --- a/fs/qnx4/namei.c
> > +++ b/fs/qnx4/namei.c
> > @@ -40,9 +40,7 @@ static int qnx4_match(int len, const char *name,
> >         } else {
> >                 namelen = QNX4_SHORT_NAME_MAX;
> >         }
> > -       thislen = strlen( de->di_fname );
> > -       if ( thislen > namelen )
> > -               thislen = namelen;
> > +       thislen = strnlen(de->di_fname, namelen);
> >         if (len != thislen) {
> >                 return 0;
> >         }

Niek reported that this fix improved the situation, but he later got a crash, 
albeit at a different place (but still within the qnx4fs).

Cheers
Anders
  

On Tue, Nov 14, 2023 at 1:40 AM Anders Larsen <al@alarsen.net> wrote:
>
< Snipped>
>
> sizeof(de->di_fname) is evaluated as QNX4_SHORT_NAME_MAX already at compile
> time, see the definition of di_fname in uapi/linux/qnx4_fs.h
>
> I agree that the code is confusing, as 'de' is declared as a pointer to a
> struct qnx4_inode_entry but in reality points to a struct qnx4_link_info iff
> QNX4_FILE_LINK is set in de->di_status.
> (Note that the corresponding field dl_status in qnx4_link_info is at the same
> offset as di_status in qnx4_inode_entry - that's the disk layout.)
>

Thanks for the details, yes in  struct qnx4_inode_entry  its size
char di_fname[QNX4_SHORT_NAME_MAX];

< snipped>
>
> Niek reported that this fix improved the situation, but he later got a crash,
> albeit at a different place (but still within the qnx4fs).

Yes I saw that Niek has shared the second crash dump stack in above email thread
and also in [1] Bugzilla 218111.The dump stack of the crash looks to
be doing a similar
lookup call context, do_statx => vfs_statx => filename_lookup =>
qn4x_lookup => fortify_panic ( )
[1] https://bugzilla.kernel.org/show_bug.cgi?id=218111#c4

But  I also see a softlockup also in the dump stack, so something in
their environment
is causing softlock ups.  And that tallies with the symptoms of system
freeze that Niek
mentioned " I can mount and view the directories, but after several hours
my system froze up again."

watchdog: BUG: soft lockup - CPU#7 stuck for 26s! [pool-gvfsd-admi:31952]   <<<<

It's possible the softlockups were occurring on fews of the CPUs on the system
for a few hours before the crash occurred that caused a system slow down.

BR,
Ronald
  

On Sun, Nov 12, 2023 at 07:53:53PM +1000, Ronald Monthero wrote:
> qnx4 dir name length can vary to be of maximum size
> QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> 'link info' entry is stored and the status byte is set.
> So to avoid buffer overflow check di_fname length
> fetched from (struct qnx4_inode_entry *)
> before use in strlen to avoid buffer overflow.
> 
> panic context
> [ 4849.636861] detected buffer overflow in strlen
> [ 4849.636897] ------------[ cut here ]------------
> [ 4849.636902] kernel BUG at lib/string.c:1165!
> [ 4849.636917] invalid opcode: 0000 [#2] SMP PTI
> ..
> [ 4849.637047] Call Trace:
> [ 4849.637053]  <TASK>
> [ 4849.637059]  ? show_trace_log_lvl+0x1d6/0x2ea
> [ 4849.637075]  ? show_trace_log_lvl+0x1d6/0x2ea
> [ 4849.637095]  ? qnx4_find_entry.cold+0xc/0x18 [qnx4]
> [ 4849.637111]  ? show_regs.part.0+0x23/0x29
> [ 4849.637123]  ? __die_body.cold+0x8/0xd
> [ 4849.637135]  ? __die+0x2b/0x37
> [ 4849.637147]  ? die+0x30/0x60
> [ 4849.637161]  ? do_trap+0xbe/0x100
> [ 4849.637171]  ? do_error_trap+0x6f/0xb0
> [ 4849.637180]  ? fortify_panic+0x13/0x15
> [ 4849.637192]  ? exc_invalid_op+0x53/0x70
> [ 4849.637203]  ? fortify_panic+0x13/0x15
> [ 4849.637215]  ? asm_exc_invalid_op+0x1b/0x20
> [ 4849.637228]  ? fortify_panic+0x13/0x15
> [ 4849.637240]  ? fortify_panic+0x13/0x15
> [ 4849.637251]  qnx4_find_entry.cold+0xc/0x18 [qnx4]
> [ 4849.637264]  qnx4_lookup+0x3c/0xa0 [qnx4]
> [ 4849.637275]  __lookup_slow+0x85/0x150
> [ 4849.637291]  walk_component+0x145/0x1c0
> [ 4849.637304]  ? path_init+0x2c0/0x3f0
> [ 4849.637316]  path_lookupat+0x6e/0x1c0
> [ 4849.637330]  filename_lookup+0xcf/0x1d0
> [ 4849.637341]  ? __check_object_size+0x1d/0x30
> [ 4849.637354]  ? strncpy_from_user+0x44/0x150
> [ 4849.637365]  ? getname_flags.part.0+0x4c/0x1b0
> [ 4849.637375]  user_path_at_empty+0x3f/0x60
> [ 4849.637383]  vfs_statx+0x7a/0x130
> [ 4849.637393]  do_statx+0x45/0x80
> ..
> 
> Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> ---
>  fs/qnx4/namei.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..825b891a52b3 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
>  	} else {
>  		namelen = QNX4_SHORT_NAME_MAX;
>  	}
> +
> +	/** qnx4 dir name length can vary, check the di_fname
> +	 * fetched from (struct qnx4_inode_entry *) before use in
> +	 * strlen to avoid panic due to buffer overflow"
> +	 */

Style nit: this comment should start with just "/*" alone, like:

	/*
	 * qnx4 dir name ...

> +	if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> +		return -ENAMETOOLONG;
>  	thislen = strlen( de->di_fname );

de->di_fname is:

struct qnx4_inode_entry {
        char            di_fname[QNX4_SHORT_NAME_MAX];
	...

#define QNX4_SHORT_NAME_MAX     16
#define QNX4_NAME_MAX           48

It's always going to have a max of QNX4_SHORT_NAME_MAX. Is any of this
code correct if namelen ends up being QNX4_NAME_MAX? It'll be reading
past the end of di_fname.

Is bh->b_data actually struct qnx4_inode_entry ?

-Kees

>  	if ( thislen > namelen )
>  		thislen = namelen;
> -- 
> 2.34.1
>
  

On Thu, Nov 16, 2023 at 06:29:59AM -0800, Kees Cook wrote:
> On Sun, Nov 12, 2023 at 07:53:53PM +1000, Ronald Monthero wrote:
> > qnx4 dir name length can vary to be of maximum size
> > QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> > 'link info' entry is stored and the status byte is set.
> > So to avoid buffer overflow check di_fname length
> > fetched from (struct qnx4_inode_entry *)
> > before use in strlen to avoid buffer overflow.
> > 
> > panic context
> > [ 4849.636861] detected buffer overflow in strlen
> > [ 4849.636897] ------------[ cut here ]------------
> > [ 4849.636902] kernel BUG at lib/string.c:1165!
> > [ 4849.636917] invalid opcode: 0000 [#2] SMP PTI
> > ..
> > [ 4849.637047] Call Trace:
> > [ 4849.637053]  <TASK>
> > [ 4849.637059]  ? show_trace_log_lvl+0x1d6/0x2ea
> > [ 4849.637075]  ? show_trace_log_lvl+0x1d6/0x2ea
> > [ 4849.637095]  ? qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > [ 4849.637111]  ? show_regs.part.0+0x23/0x29
> > [ 4849.637123]  ? __die_body.cold+0x8/0xd
> > [ 4849.637135]  ? __die+0x2b/0x37
> > [ 4849.637147]  ? die+0x30/0x60
> > [ 4849.637161]  ? do_trap+0xbe/0x100
> > [ 4849.637171]  ? do_error_trap+0x6f/0xb0
> > [ 4849.637180]  ? fortify_panic+0x13/0x15
> > [ 4849.637192]  ? exc_invalid_op+0x53/0x70
> > [ 4849.637203]  ? fortify_panic+0x13/0x15
> > [ 4849.637215]  ? asm_exc_invalid_op+0x1b/0x20
> > [ 4849.637228]  ? fortify_panic+0x13/0x15
> > [ 4849.637240]  ? fortify_panic+0x13/0x15
> > [ 4849.637251]  qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > [ 4849.637264]  qnx4_lookup+0x3c/0xa0 [qnx4]
> > [ 4849.637275]  __lookup_slow+0x85/0x150
> > [ 4849.637291]  walk_component+0x145/0x1c0
> > [ 4849.637304]  ? path_init+0x2c0/0x3f0
> > [ 4849.637316]  path_lookupat+0x6e/0x1c0
> > [ 4849.637330]  filename_lookup+0xcf/0x1d0
> > [ 4849.637341]  ? __check_object_size+0x1d/0x30
> > [ 4849.637354]  ? strncpy_from_user+0x44/0x150
> > [ 4849.637365]  ? getname_flags.part.0+0x4c/0x1b0
> > [ 4849.637375]  user_path_at_empty+0x3f/0x60
> > [ 4849.637383]  vfs_statx+0x7a/0x130
> > [ 4849.637393]  do_statx+0x45/0x80
> > ..
> > 
> > Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> > ---
> >  fs/qnx4/namei.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > index 8d72221735d7..825b891a52b3 100644
> > --- a/fs/qnx4/namei.c
> > +++ b/fs/qnx4/namei.c
> > @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
> >  	} else {
> >  		namelen = QNX4_SHORT_NAME_MAX;
> >  	}
> > +
> > +	/** qnx4 dir name length can vary, check the di_fname
> > +	 * fetched from (struct qnx4_inode_entry *) before use in
> > +	 * strlen to avoid panic due to buffer overflow"
> > +	 */
> 
> Style nit: this comment should start with just "/*" alone, like:
> 
> 	/*
> 	 * qnx4 dir name ...
> 
> > +	if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> > +		return -ENAMETOOLONG;
> >  	thislen = strlen( de->di_fname );
> 
> de->di_fname is:
> 
> struct qnx4_inode_entry {
>         char            di_fname[QNX4_SHORT_NAME_MAX];
> 	...
> 
> #define QNX4_SHORT_NAME_MAX     16
> #define QNX4_NAME_MAX           48
> 
> It's always going to have a max of QNX4_SHORT_NAME_MAX. Is any of this
> code correct if namelen ends up being QNX4_NAME_MAX? It'll be reading
> past the end of di_fname.
> 
> Is bh->b_data actually struct qnx4_inode_entry ?

Ah-ha, it looks like it's _not_:

        if (!(bh = qnx4_find_entry(len, dir, name, &de, &ino)))
                goto out;
        /* The entry is linked, let's get the real info */
        if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
                lnk = (struct qnx4_link_info *) de;

It seems that entries may be either struct qnx4_inode_entry or struct
qnx4_link_info but it's not captured in a union.

This needs to be fixed by not lying to the compiler about what is there.

How about this?


diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
index 8d72221735d7..3cd20065bcfa 100644
--- a/fs/qnx4/namei.c
+++ b/fs/qnx4/namei.c
@@ -26,31 +26,39 @@
 static int qnx4_match(int len, const char *name,
 		      struct buffer_head *bh, unsigned long *offset)
 {
-	struct qnx4_inode_entry *de;
-	int namelen, thislen;
+	union qnx4_dir_entry *de;
+	char *entry_fname;
+	int entry_len, entry_max_len;
 
 	if (bh == NULL) {
 		printk(KERN_WARNING "qnx4: matching unassigned buffer !\n");
 		return 0;
 	}
-	de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
+	de = (union qnx4_dir_entry *) (bh->b_data + *offset);
 	*offset += QNX4_DIR_ENTRY_SIZE;
-	if ((de->di_status & QNX4_FILE_LINK) != 0) {
-		namelen = QNX4_NAME_MAX;
-	} else {
-		namelen = QNX4_SHORT_NAME_MAX;
-	}
-	thislen = strlen( de->di_fname );
-	if ( thislen > namelen )
-		thislen = namelen;
-	if (len != thislen) {
+
+	switch (de->inode.di_status) {
+	case QNX4_FILE_LINK:
+		entry_fname = de->link.dl_fname;
+		entry_max_len = sizeof(de->link.dl_fname);
+		break;
+	case QNX4_FILE_USED:
+		entry_fname = de->inode.di_fname;
+		entry_max_len = sizeof(de->inode.di_fname);
+		break;
+	default:
 		return 0;
 	}
-	if (strncmp(name, de->di_fname, len) == 0) {
-		if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) != 0) {
-			return 1;
-		}
-	}
+
+	/* Directory entry may not be %NUL-terminated. */
+	entry_len = strnlen(entry_fname, entry_max_len);
+
+	if (len != entry_len)
+		return 0;
+
+	if (strncmp(name, entry_fname, len) == 0)
+		return 1;
+
 	return 0;
 }
 
diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
index 31487325d265..e033dbe1e009 100644
--- a/include/uapi/linux/qnx4_fs.h
+++ b/include/uapi/linux/qnx4_fs.h
@@ -68,6 +68,13 @@ struct qnx4_link_info {
 	__u8		dl_status;
 };
 
+union qnx4_dir_entry {
+	struct qnx4_inode_entry inode;
+	struct qnx4_link_info link;
+};
+_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
+	       offsetof(struct qnx4_link_info, dl_status));
+
 struct qnx4_xblk {
 	__le32		xblk_next_xblk;
 	__le32		xblk_prev_xblk;
  

On 2023-11-16 15:58 Kees Cook wrote:
> On Thu, Nov 16, 2023 at 06:29:59AM -0800, Kees Cook wrote:
> > On Sun, Nov 12, 2023 at 07:53:53PM +1000, Ronald Monthero wrote:
> > > qnx4 dir name length can vary to be of maximum size
> > > QNX4_NAME_MAX or QNX4_SHORT_NAME_MAX depending on whether
> > > 'link info' entry is stored and the status byte is set.
> > > So to avoid buffer overflow check di_fname length
> > > fetched from (struct qnx4_inode_entry *)
> > > before use in strlen to avoid buffer overflow.
> > > 
> > > panic context
> > > [ 4849.636861] detected buffer overflow in strlen
> > > [ 4849.636897] ------------[ cut here ]------------
> > > [ 4849.636902] kernel BUG at lib/string.c:1165!
> > > [ 4849.636917] invalid opcode: 0000 [#2] SMP PTI
> > > ..
> > > [ 4849.637047] Call Trace:
> > > [ 4849.637053]  <TASK>
> > > [ 4849.637059]  ? show_trace_log_lvl+0x1d6/0x2ea
> > > [ 4849.637075]  ? show_trace_log_lvl+0x1d6/0x2ea
> > > [ 4849.637095]  ? qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > > [ 4849.637111]  ? show_regs.part.0+0x23/0x29
> > > [ 4849.637123]  ? __die_body.cold+0x8/0xd
> > > [ 4849.637135]  ? __die+0x2b/0x37
> > > [ 4849.637147]  ? die+0x30/0x60
> > > [ 4849.637161]  ? do_trap+0xbe/0x100
> > > [ 4849.637171]  ? do_error_trap+0x6f/0xb0
> > > [ 4849.637180]  ? fortify_panic+0x13/0x15
> > > [ 4849.637192]  ? exc_invalid_op+0x53/0x70
> > > [ 4849.637203]  ? fortify_panic+0x13/0x15
> > > [ 4849.637215]  ? asm_exc_invalid_op+0x1b/0x20
> > > [ 4849.637228]  ? fortify_panic+0x13/0x15
> > > [ 4849.637240]  ? fortify_panic+0x13/0x15
> > > [ 4849.637251]  qnx4_find_entry.cold+0xc/0x18 [qnx4]
> > > [ 4849.637264]  qnx4_lookup+0x3c/0xa0 [qnx4]
> > > [ 4849.637275]  __lookup_slow+0x85/0x150
> > > [ 4849.637291]  walk_component+0x145/0x1c0
> > > [ 4849.637304]  ? path_init+0x2c0/0x3f0
> > > [ 4849.637316]  path_lookupat+0x6e/0x1c0
> > > [ 4849.637330]  filename_lookup+0xcf/0x1d0
> > > [ 4849.637341]  ? __check_object_size+0x1d/0x30
> > > [ 4849.637354]  ? strncpy_from_user+0x44/0x150
> > > [ 4849.637365]  ? getname_flags.part.0+0x4c/0x1b0
> > > [ 4849.637375]  user_path_at_empty+0x3f/0x60
> > > [ 4849.637383]  vfs_statx+0x7a/0x130
> > > [ 4849.637393]  do_statx+0x45/0x80
> > > ..
> > > 
> > > Signed-off-by: Ronald Monthero <debug.penguin32@gmail.com>
> > > ---
> > > 
> > >  fs/qnx4/namei.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > > index 8d72221735d7..825b891a52b3 100644
> > > --- a/fs/qnx4/namei.c
> > > +++ b/fs/qnx4/namei.c
> > > @@ -40,6 +40,13 @@ static int qnx4_match(int len, const char *name,
> > > 
> > >  	} else {
> > >  	
> > >  		namelen = QNX4_SHORT_NAME_MAX;
> > >  	
> > >  	}
> > > 
> > > +
> > > +	/** qnx4 dir name length can vary, check the di_fname
> > > +	 * fetched from (struct qnx4_inode_entry *) before use in
> > > +	 * strlen to avoid panic due to buffer overflow"
> > > +	 */
> > 
> > Style nit: this comment should start with just "/*" alone, like:
> > 	/*
> > 	
> > 	 * qnx4 dir name ...
> > 	 
> > > +	if (strnlen(de->di_fname, namelen) >= sizeof(de->di_fname))
> > > +		return -ENAMETOOLONG;
> > > 
> > >  	thislen = strlen( de->di_fname );
> > 
> > de->di_fname is:
> > 
> > struct qnx4_inode_entry {
> > 
> >         char            di_fname[QNX4_SHORT_NAME_MAX];
> > 	
> > 	...
> > 
> > #define QNX4_SHORT_NAME_MAX     16
> > #define QNX4_NAME_MAX           48
> > 
> > It's always going to have a max of QNX4_SHORT_NAME_MAX. Is any of this
> > code correct if namelen ends up being QNX4_NAME_MAX? It'll be reading
> > past the end of di_fname.
> > 
> > Is bh->b_data actually struct qnx4_inode_entry ?
> 
> Ah-ha, it looks like it's _not_:
> 
>         if (!(bh = qnx4_find_entry(len, dir, name, &de, &ino)))
>                 goto out;
>         /* The entry is linked, let's get the real info */
>         if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
>                 lnk = (struct qnx4_link_info *) de;
> 
> It seems that entries may be either struct qnx4_inode_entry or struct
> qnx4_link_info but it's not captured in a union.
> 
> This needs to be fixed by not lying to the compiler about what is there.
> 
> How about this?

The switch won't work since the _status field is a bit-field, so we should 
rather reuse the similar union-logic already present in fs/qnx4/dir.c

> diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> index 8d72221735d7..3cd20065bcfa 100644
> --- a/fs/qnx4/namei.c
> +++ b/fs/qnx4/namei.c
> @@ -26,31 +26,39 @@
>  static int qnx4_match(int len, const char *name,
>  		      struct buffer_head *bh, unsigned long *offset)
>  {
> -	struct qnx4_inode_entry *de;
> -	int namelen, thislen;
> +	union qnx4_dir_entry *de;
> +	char *entry_fname;
> +	int entry_len, entry_max_len;
> 
>  	if (bh == NULL) {
>  		printk(KERN_WARNING "qnx4: matching unassigned buffer !
\n");
>  		return 0;
>  	}
> -	de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
> +	de = (union qnx4_dir_entry *) (bh->b_data + *offset);
>  	*offset += QNX4_DIR_ENTRY_SIZE;
> -	if ((de->di_status & QNX4_FILE_LINK) != 0) {
> -		namelen = QNX4_NAME_MAX;
> -	} else {
> -		namelen = QNX4_SHORT_NAME_MAX;
> -	}
> -	thislen = strlen( de->di_fname );
> -	if ( thislen > namelen )
> -		thislen = namelen;
> -	if (len != thislen) {
> +
> +	switch (de->inode.di_status) {
> +	case QNX4_FILE_LINK:
> +		entry_fname = de->link.dl_fname;
> +		entry_max_len = sizeof(de->link.dl_fname);
> +		break;
> +	case QNX4_FILE_USED:
> +		entry_fname = de->inode.di_fname;
> +		entry_max_len = sizeof(de->inode.di_fname);
> +		break;
> +	default:
>  		return 0;
>  	}
> -	if (strncmp(name, de->di_fname, len) == 0) {
> -		if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) !
= 0) {
> -			return 1;
> -		}
> -	}
> +
> +	/* Directory entry may not be %NUL-terminated. */
> +	entry_len = strnlen(entry_fname, entry_max_len);
> +
> +	if (len != entry_len)
> +		return 0;
> +
> +	if (strncmp(name, entry_fname, len) == 0)
> +		return 1;
> +
>  	return 0;
>  }
> 
> diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
> index 31487325d265..e033dbe1e009 100644
> --- a/include/uapi/linux/qnx4_fs.h
> +++ b/include/uapi/linux/qnx4_fs.h
> @@ -68,6 +68,13 @@ struct qnx4_link_info {
>  	__u8		dl_status;
>  };
> 
> +union qnx4_dir_entry {
> +	struct qnx4_inode_entry inode;
> +	struct qnx4_link_info link;
> +};
> +_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
> +	       offsetof(struct qnx4_link_info, dl_status));
> +
>  struct qnx4_xblk {
>  	__le32		xblk_next_xblk;
>  	__le32		xblk_prev_xblk;
  

On Thu, Nov 16, 2023 at 05:48:20PM +0100, Anders Larsen wrote:
> On 2023-11-16 15:58 Kees Cook wrote:
> >         if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
> >                 lnk = (struct qnx4_link_info *) de;
> > 
> > It seems that entries may be either struct qnx4_inode_entry or struct
> > qnx4_link_info but it's not captured in a union.
> > 
> > This needs to be fixed by not lying to the compiler about what is there.
> > 
> > How about this?
> 
> > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > index 8d72221735d7..3cd20065bcfa 100644
> > --- a/fs/qnx4/namei.c
> > +++ b/fs/qnx4/namei.c
> > @@ -26,31 +26,39 @@
> >  static int qnx4_match(int len, const char *name,
> >  		      struct buffer_head *bh, unsigned long *offset)
> >  {
> > -	struct qnx4_inode_entry *de;
> > -	int namelen, thislen;
> > +	union qnx4_dir_entry *de;
> > +	char *entry_fname;
> > +	int entry_len, entry_max_len;
> > 
> >  	if (bh == NULL) {
> >  		printk(KERN_WARNING "qnx4: matching unassigned buffer !
> \n");
> >  		return 0;
> >  	}
> > -	de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
> > +	de = (union qnx4_dir_entry *) (bh->b_data + *offset);
> >  	*offset += QNX4_DIR_ENTRY_SIZE;
> > -	if ((de->di_status & QNX4_FILE_LINK) != 0) {
> > -		namelen = QNX4_NAME_MAX;
> > -	} else {
> > -		namelen = QNX4_SHORT_NAME_MAX;
> > -	}
> > -	thislen = strlen( de->di_fname );
> > -	if ( thislen > namelen )
> > -		thislen = namelen;
> > -	if (len != thislen) {
> > +
> > +	switch (de->inode.di_status) {
> > +	case QNX4_FILE_LINK:
> > +		entry_fname = de->link.dl_fname;
> > +		entry_max_len = sizeof(de->link.dl_fname);
> > +		break;
> > +	case QNX4_FILE_USED:
> > +		entry_fname = de->inode.di_fname;
> > +		entry_max_len = sizeof(de->inode.di_fname);
> > +		break;
> > +	default:
> >  		return 0;
> >  	}
> 
> The switch won't work since the _status field is a bit-field, so we should 
> rather reuse the similar union-logic already present in fs/qnx4/dir.c

Ah, okay, LINK and USED might both be there. And perfect, yes, it looks
like the union qnx4_directory_entry in fs/qnx4/dir.c would be perfect.

-Kees

> > -	if (strncmp(name, de->di_fname, len) == 0) {
> > -		if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) !
> = 0) {
> > -			return 1;
> > -		}
> > -	}
> > +
> > +	/* Directory entry may not be %NUL-terminated. */
> > +	entry_len = strnlen(entry_fname, entry_max_len);
> > +
> > +	if (len != entry_len)
> > +		return 0;
> > +
> > +	if (strncmp(name, entry_fname, len) == 0)
> > +		return 1;
> > +
> >  	return 0;
> >  }
> > 
> > diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
> > index 31487325d265..e033dbe1e009 100644
> > --- a/include/uapi/linux/qnx4_fs.h
> > +++ b/include/uapi/linux/qnx4_fs.h
> > @@ -68,6 +68,13 @@ struct qnx4_link_info {
> >  	__u8		dl_status;
> >  };
> > 
> > +union qnx4_dir_entry {
> > +	struct qnx4_inode_entry inode;
> > +	struct qnx4_link_info link;
> > +};
> > +_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
> > +	       offsetof(struct qnx4_link_info, dl_status));
> > +
> >  struct qnx4_xblk {
> >  	__le32		xblk_next_xblk;
> >  	__le32		xblk_prev_xblk;
> 
> 
> 
>
  

Thank you Kees and Anders, Cheers

BR,
Ronald

On Fri, Nov 17, 2023 at 4:26 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Thu, Nov 16, 2023 at 05:48:20PM +0100, Anders Larsen wrote:
> > On 2023-11-16 15:58 Kees Cook wrote:
> > >         if ((de->di_status & QNX4_FILE_LINK) == QNX4_FILE_LINK) {
> > >                 lnk = (struct qnx4_link_info *) de;
> > >
> > > It seems that entries may be either struct qnx4_inode_entry or struct
> > > qnx4_link_info but it's not captured in a union.
> > >
> > > This needs to be fixed by not lying to the compiler about what is there.
> > >
> > > How about this?
> >
> > > diff --git a/fs/qnx4/namei.c b/fs/qnx4/namei.c
> > > index 8d72221735d7..3cd20065bcfa 100644
> > > --- a/fs/qnx4/namei.c
> > > +++ b/fs/qnx4/namei.c
> > > @@ -26,31 +26,39 @@
> > >  static int qnx4_match(int len, const char *name,
> > >                   struct buffer_head *bh, unsigned long *offset)
> > >  {
> > > -   struct qnx4_inode_entry *de;
> > > -   int namelen, thislen;
> > > +   union qnx4_dir_entry *de;
> > > +   char *entry_fname;
> > > +   int entry_len, entry_max_len;
> > >
> > >     if (bh == NULL) {
> > >             printk(KERN_WARNING "qnx4: matching unassigned buffer !
> > \n");
> > >             return 0;
> > >     }
> > > -   de = (struct qnx4_inode_entry *) (bh->b_data + *offset);
> > > +   de = (union qnx4_dir_entry *) (bh->b_data + *offset);
> > >     *offset += QNX4_DIR_ENTRY_SIZE;
> > > -   if ((de->di_status & QNX4_FILE_LINK) != 0) {
> > > -           namelen = QNX4_NAME_MAX;
> > > -   } else {
> > > -           namelen = QNX4_SHORT_NAME_MAX;
> > > -   }
> > > -   thislen = strlen( de->di_fname );
> > > -   if ( thislen > namelen )
> > > -           thislen = namelen;
> > > -   if (len != thislen) {
> > > +
> > > +   switch (de->inode.di_status) {
> > > +   case QNX4_FILE_LINK:
> > > +           entry_fname = de->link.dl_fname;
> > > +           entry_max_len = sizeof(de->link.dl_fname);
> > > +           break;
> > > +   case QNX4_FILE_USED:
> > > +           entry_fname = de->inode.di_fname;
> > > +           entry_max_len = sizeof(de->inode.di_fname);
> > > +           break;
> > > +   default:
> > >             return 0;
> > >     }
> >
> > The switch won't work since the _status field is a bit-field, so we should
> > rather reuse the similar union-logic already present in fs/qnx4/dir.c
>
> Ah, okay, LINK and USED might both be there. And perfect, yes, it looks
> like the union qnx4_directory_entry in fs/qnx4/dir.c would be perfect.
>
> -Kees
>
> > > -   if (strncmp(name, de->di_fname, len) == 0) {
> > > -           if ((de->di_status & (QNX4_FILE_USED|QNX4_FILE_LINK)) !
> > = 0) {
> > > -                   return 1;
> > > -           }
> > > -   }
> > > +
> > > +   /* Directory entry may not be %NUL-terminated. */
> > > +   entry_len = strnlen(entry_fname, entry_max_len);
> > > +
> > > +   if (len != entry_len)
> > > +           return 0;
> > > +
> > > +   if (strncmp(name, entry_fname, len) == 0)
> > > +           return 1;
> > > +
> > >     return 0;
> > >  }
> > >
> > > diff --git a/include/uapi/linux/qnx4_fs.h b/include/uapi/linux/qnx4_fs.h
> > > index 31487325d265..e033dbe1e009 100644
> > > --- a/include/uapi/linux/qnx4_fs.h
> > > +++ b/include/uapi/linux/qnx4_fs.h
> > > @@ -68,6 +68,13 @@ struct qnx4_link_info {
> > >     __u8            dl_status;
> > >  };
> > >
> > > +union qnx4_dir_entry {
> > > +   struct qnx4_inode_entry inode;
> > > +   struct qnx4_link_info link;
> > > +};
> > > +_Static_assert(offsetof(struct qnx4_inode_entry, di_status) ==
> > > +          offsetof(struct qnx4_link_info, dl_status));
> > > +
> > >  struct qnx4_xblk {
> > >     __le32          xblk_next_xblk;
> > >     __le32          xblk_prev_xblk;
> >
> >
> >
> >
>
> --
> Kees Cook