[v4,4/4] tracing/probes: Fix to record 0-length data_loc in fetch_store_string*() if fails
Commit Message
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Fix to record 0-length data to data_loc in fetch_store_string*() if it fails
to get the string data.
Currently those expect that the data_loc is updated by store_trace_args() if
it returns the error code. However, that does not work correctly if the
argument is an array of strings. In that case, store_trace_args() only clears
the first entry of the array (which may have no error) and leaves other
entries. So it should be cleared by fetch_store_string*() itself.
Also, 'dyndata' and 'maxlen' in store_trace_args() should be updated
only if it is used (ret > 0 and argument is a dynamic data.)
Fixes: 40b53b771806 ("tracing: probeevent: Add array type support")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v4:
- Simplify the updating data_loc code with set_data_loc().
---
kernel/trace/trace_probe_kernel.h | 13 +++++++++----
kernel/trace/trace_probe_tmpl.h | 4 +---
kernel/trace/trace_uprobe.c | 3 ++-
3 files changed, 12 insertions(+), 8 deletions(-)
Comments
On Tue, 11 Jul 2023 11:11:51 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> --- a/kernel/trace/trace_probe_tmpl.h
> +++ b/kernel/trace/trace_probe_tmpl.h
> @@ -267,9 +267,7 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
> if (unlikely(arg->dynamic))
> *dl = make_data_loc(maxlen, dyndata - base);
> ret = process_fetch_insn(arg->code, rec, dl, base);
> - if (unlikely(ret < 0 && arg->dynamic)) {
> - *dl = make_data_loc(0, dyndata - base);
> - } else {
> + if (unlikely(ret > 0 && arg->dynamic)) {
To match the current code, that should be:
if (likely(ret >= 0 || !arg->dynamic)) {
But I'm guessing that the original code was buggy, as the else block should
only have been processed if arg->dynamic was set? That is, it should have been:
if (arg->dynamic) {
if (unlikely(ret < 0)) {
*dl = make_data_loc(0, dyndata - base);
} else {
dyndata += ret;
maxlen -= ret;
}
}
I guess you only want to update if arg->dynamic is true (even though that
wasn't the case before :-/) But in any case, I think you want likely() and
not unlikely().
if (arg->dynamic && likely(ret > 0)) {
That is, if we only want to updated this if the arg is dynamic.
And I don't think that the arg->dynamic() should have likely/unlikely
around it, as that's determined by user space, and the kernel should not be
adding assumptions about what user space wants.
-- Steve
> dyndata += ret;
> maxlen -= ret;
> }
On Mon, 10 Jul 2023 23:34:00 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Tue, 11 Jul 2023 11:11:51 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
>
> > --- a/kernel/trace/trace_probe_tmpl.h
> > +++ b/kernel/trace/trace_probe_tmpl.h
> > @@ -267,9 +267,7 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
> > if (unlikely(arg->dynamic))
> > *dl = make_data_loc(maxlen, dyndata - base);
> > ret = process_fetch_insn(arg->code, rec, dl, base);
> > - if (unlikely(ret < 0 && arg->dynamic)) {
> > - *dl = make_data_loc(0, dyndata - base);
> > - } else {
> > + if (unlikely(ret > 0 && arg->dynamic)) {
>
> To match the current code, that should be:
>
> if (likely(ret >= 0 || !arg->dynamic)) {
>
> But I'm guessing that the original code was buggy, as the else block should
> only have been processed if arg->dynamic was set?
Good point, yes, that's right. Since dyndata and maxlen is only used when
arg->dynamic == true, we don't have to care about that.
> That is, it should have been:
>
> if (arg->dynamic) {
> if (unlikely(ret < 0)) {
> *dl = make_data_loc(0, dyndata - base);
> } else {
> dyndata += ret;
> maxlen -= ret;
> }
> }
>
>
> I guess you only want to update if arg->dynamic is true (even though that
> wasn't the case before :-/) But in any case, I think you want likely() and
> not unlikely().
>
> if (arg->dynamic && likely(ret > 0)) {
>
> That is, if we only want to updated this if the arg is dynamic.
Indeed.
>
> And I don't think that the arg->dynamic() should have likely/unlikely
> around it, as that's determined by user space, and the kernel should not be
> adding assumptions about what user space wants.
OK.
Let me fix that with a new patch because it is another bug.
Thanks,
>
> -- Steve
>
> > dyndata += ret;
> > maxlen -= ret;
> > }
@@ -37,6 +37,13 @@ fetch_store_strlen(unsigned long addr)
return (ret < 0) ? ret : len;
}
+static nokprobe_inline void set_data_loc(int ret, void *dest, void *__dest, void *base)
+{
+ if (ret < 0)
+ ret = 0;
+ *(u32 *)dest = make_data_loc(ret, __dest - base);
+}
+
/*
* Fetch a null-terminated string from user. Caller MUST set *(u32 *)buf
* with max length and relative data location.
@@ -55,8 +62,7 @@ fetch_store_string_user(unsigned long addr, void *dest, void *base)
__dest = get_loc_data(dest, base);
ret = strncpy_from_user_nofault(__dest, uaddr, maxlen);
- if (ret >= 0)
- *(u32 *)dest = make_data_loc(ret, __dest - base);
+ set_data_loc(ret, dest, __dest, base);
return ret;
}
@@ -87,8 +93,7 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
* probing.
*/
ret = strncpy_from_kernel_nofault(__dest, (void *)addr, maxlen);
- if (ret >= 0)
- *(u32 *)dest = make_data_loc(ret, __dest - base);
+ set_data_loc(ret, dest, __dest, base);
return ret;
}
@@ -267,9 +267,7 @@ store_trace_args(void *data, struct trace_probe *tp, void *rec,
if (unlikely(arg->dynamic))
*dl = make_data_loc(maxlen, dyndata - base);
ret = process_fetch_insn(arg->code, rec, dl, base);
- if (unlikely(ret < 0 && arg->dynamic)) {
- *dl = make_data_loc(0, dyndata - base);
- } else {
+ if (unlikely(ret > 0 && arg->dynamic)) {
dyndata += ret;
maxlen -= ret;
}
@@ -170,7 +170,8 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
*/
ret++;
*(u32 *)dest = make_data_loc(ret, (void *)dst - base);
- }
+ } else
+ *(u32 *)dest = make_data_loc(0, (void *)dst - base);
return ret;
}