diff mbox series

[1/2] ext2: fix race between setxattr and write back

Message ID 20230811033857.1800578-2-yebin10@huawei.com
State New
Headers
Series fix race between setxattr and write back |

Commit Message

Ye Bin Aug. 11, 2023, 3:38 a.m. UTC 
  There's a issue as follows:
Block Allocation Reservation Windows Map (ext2_try_to_allocate_with_rsv):
reservation window 0x000000006f105382 start: 0, end: 0
reservation window 0x000000008fd1a555 start: 1044, end: 1059
Window map complete.
kernel BUG at fs/ext2/balloc.c:1158!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:ext2_try_to_allocate_with_rsv.isra.0+0x15c4/0x1800
Call Trace:
 <TASK>
 ext2_new_blocks+0x935/0x1690
 ext2_new_block+0x73/0xa0
 ext2_xattr_set2+0x74f/0x1730
 ext2_xattr_set+0x12b6/0x2260
 ext2_xattr_user_set+0x9c/0x110
 __vfs_setxattr+0x139/0x1d0
 __vfs_setxattr_noperm+0xfc/0x370
 __vfs_setxattr_locked+0x205/0x2c0
 vfs_setxattr+0x19d/0x3b0
 do_setxattr+0xff/0x220
 setxattr+0x123/0x150
 path_setxattr+0x193/0x1e0
 __x64_sys_setxattr+0xc8/0x170
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Above issue may happens as follows:
        setxattr                             write back
ext2_xattr_set
  ext2_xattr_set2
    ext2_new_block
      ext2_new_blocks
        ext2_try_to_allocate_with_rsv
	  alloc_new_reservation
	  --> group=0 [0, 1023] rsv [1016, 1023]
	                                do_writepages
					  mpage_writepages
					    write_cache_pages
					      __mpage_writepage
					        ext2_get_block
						  ext2_get_blocks
						   ext2_alloc_branch
						    ext2_new_blocks
						     ext2_try_to_allocate_with_rsv
						       alloc_new_reservation
		                     -->group=1 [1024, 2047] rsv [1044, 1059]
	  if ((my_rsv->rsv_start > group_last_block) ||
	      (my_rsv->rsv_end < group_first_block)
	      rsv_window_dump
	      BUG();
Now ext2 mkwrite delay allocate new blocks. So there maybe allocate blocks when
do write back. However, there is no concurrent protection between
ext2_xattr_set() and do_writepages().
To solve about issue hold '&ei->truncate_mutex' lock when new block for xattr.

Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/ext2/balloc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Comments

Jan Kara Aug. 14, 2023, 12:46 p.m. UTC | #1 
On Fri 11-08-23 11:38:56, Ye Bin wrote:
> There's a issue as follows:
> Block Allocation Reservation Windows Map (ext2_try_to_allocate_with_rsv):
> reservation window 0x000000006f105382 start: 0, end: 0
> reservation window 0x000000008fd1a555 start: 1044, end: 1059
> Window map complete.
> kernel BUG at fs/ext2/balloc.c:1158!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> RIP: 0010:ext2_try_to_allocate_with_rsv.isra.0+0x15c4/0x1800
> Call Trace:
>  <TASK>
>  ext2_new_blocks+0x935/0x1690
>  ext2_new_block+0x73/0xa0
>  ext2_xattr_set2+0x74f/0x1730
>  ext2_xattr_set+0x12b6/0x2260
>  ext2_xattr_user_set+0x9c/0x110
>  __vfs_setxattr+0x139/0x1d0
>  __vfs_setxattr_noperm+0xfc/0x370
>  __vfs_setxattr_locked+0x205/0x2c0
>  vfs_setxattr+0x19d/0x3b0
>  do_setxattr+0xff/0x220
>  setxattr+0x123/0x150
>  path_setxattr+0x193/0x1e0
>  __x64_sys_setxattr+0xc8/0x170
>  do_syscall_64+0x35/0x80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Above issue may happens as follows:
>         setxattr                             write back
> ext2_xattr_set
>   ext2_xattr_set2
>     ext2_new_block
>       ext2_new_blocks
>         ext2_try_to_allocate_with_rsv
> 	  alloc_new_reservation
> 	  --> group=0 [0, 1023] rsv [1016, 1023]
> 	                                do_writepages
> 					  mpage_writepages
> 					    write_cache_pages
> 					      __mpage_writepage
> 					        ext2_get_block
> 						  ext2_get_blocks
> 						   ext2_alloc_branch
> 						    ext2_new_blocks
> 						     ext2_try_to_allocate_with_rsv
> 						       alloc_new_reservation
> 		                     -->group=1 [1024, 2047] rsv [1044, 1059]
> 	  if ((my_rsv->rsv_start > group_last_block) ||
> 	      (my_rsv->rsv_end < group_first_block)
> 	      rsv_window_dump
> 	      BUG();
> Now ext2 mkwrite delay allocate new blocks. So there maybe allocate blocks when
> do write back. However, there is no concurrent protection between
> ext2_xattr_set() and do_writepages().
> To solve about issue hold '&ei->truncate_mutex' lock when new block for xattr.
> 
> Signed-off-by: Ye Bin <yebin10@huawei.com>

Thanks for the patch! I agree the handling of reservation window and its
use for block allocation needs to be protected by ei->i_truncate_mutex.
However in this particular case of xattr allocation where we want to
allocate just one block which is completely independent of file data, I'd
rather choose to make ext2_new_blocks() ignore the reservation window (set
my_rsv to NULL). There's already a logic at the beginning of
ext2_new_blocks() deciding whether to use the reservation window or not and
we could extend it - probably by adding flags argument to it a introducing
a NORESERVE flag.

Also as a preparatory patch, I'd just remove ext2_new_block() and opencode
it in the xattr code since it has only that one user anyway.

								Honza



> ---
>  fs/ext2/balloc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
> index c8049c90323d..039f655febfd 100644
> --- a/fs/ext2/balloc.c
> +++ b/fs/ext2/balloc.c
> @@ -1432,8 +1432,14 @@ ext2_fsblk_t ext2_new_blocks(struct inode *inode, ext2_fsblk_t goal,
>  ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
>  {
>  	unsigned long count = 1;
> +	struct ext2_inode_info *ei = EXT2_I(inode);
> +	ext2_fsblk_t ret;
> +
> +	mutex_lock(&ei->truncate_mutex);
> +	ret = ext2_new_blocks(inode, goal, &count, errp);
> +	mutex_unlock(&ei->truncate_mutex);
>  
> -	return ext2_new_blocks(inode, goal, &count, errp);
> +	return ret;
>  }
>  
>  #ifdef EXT2FS_DEBUG
> -- 
> 2.31.1
>
Ye Bin Aug. 14, 2023, 3:42 p.m. UTC | #2 
On 2023/8/14 20:46, Jan Kara wrote:
> On Fri 11-08-23 11:38:56, Ye Bin wrote:
>> There's a issue as follows:
>> Block Allocation Reservation Windows Map (ext2_try_to_allocate_with_rsv):
>> reservation window 0x000000006f105382 start: 0, end: 0
>> reservation window 0x000000008fd1a555 start: 1044, end: 1059
>> Window map complete.
>> kernel BUG at fs/ext2/balloc.c:1158!
>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>> RIP: 0010:ext2_try_to_allocate_with_rsv.isra.0+0x15c4/0x1800
>> Call Trace:
>>   <TASK>
>>   ext2_new_blocks+0x935/0x1690
>>   ext2_new_block+0x73/0xa0
>>   ext2_xattr_set2+0x74f/0x1730
>>   ext2_xattr_set+0x12b6/0x2260
>>   ext2_xattr_user_set+0x9c/0x110
>>   __vfs_setxattr+0x139/0x1d0
>>   __vfs_setxattr_noperm+0xfc/0x370
>>   __vfs_setxattr_locked+0x205/0x2c0
>>   vfs_setxattr+0x19d/0x3b0
>>   do_setxattr+0xff/0x220
>>   setxattr+0x123/0x150
>>   path_setxattr+0x193/0x1e0
>>   __x64_sys_setxattr+0xc8/0x170
>>   do_syscall_64+0x35/0x80
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> Above issue may happens as follows:
>>          setxattr                             write back
>> ext2_xattr_set
>>    ext2_xattr_set2
>>      ext2_new_block
>>        ext2_new_blocks
>>          ext2_try_to_allocate_with_rsv
>> 	  alloc_new_reservation
>> 	  --> group=0 [0, 1023] rsv [1016, 1023]
>> 	                                do_writepages
>> 					  mpage_writepages
>> 					    write_cache_pages
>> 					      __mpage_writepage
>> 					        ext2_get_block
>> 						  ext2_get_blocks
>> 						   ext2_alloc_branch
>> 						    ext2_new_blocks
>> 						     ext2_try_to_allocate_with_rsv
>> 						       alloc_new_reservation
>> 		                     -->group=1 [1024, 2047] rsv [1044, 1059]
>> 	  if ((my_rsv->rsv_start > group_last_block) ||
>> 	      (my_rsv->rsv_end < group_first_block)
>> 	      rsv_window_dump
>> 	      BUG();
>> Now ext2 mkwrite delay allocate new blocks. So there maybe allocate blocks when
>> do write back. However, there is no concurrent protection between
>> ext2_xattr_set() and do_writepages().
>> To solve about issue hold '&ei->truncate_mutex' lock when new block for xattr.
>>
>> Signed-off-by: Ye Bin <yebin10@huawei.com>
> Thanks for the patch! I agree the handling of reservation window and its
> use for block allocation needs to be protected by ei->i_truncate_mutex.
> However in this particular case of xattr allocation where we want to
> allocate just one block which is completely independent of file data, I'd
> rather choose to make ext2_new_blocks() ignore the reservation window (set
> my_rsv to NULL). There's already a logic at the beginning of
> ext2_new_blocks() deciding whether to use the reservation window or not and
> we could extend it - probably by adding flags argument to it a introducing
> a NORESERVE flag.
>
> Also as a preparatory patch, I'd just remove ext2_new_block() and opencode
> it in the xattr code since it has only that one user anyway.
>
> 								Honza
>
Thanks for your suggestion.  I will send new version according to your 
suggestion.
>
>> ---
>>   fs/ext2/balloc.c | 8 +++++++-
>>   1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
>> index c8049c90323d..039f655febfd 100644
>> --- a/fs/ext2/balloc.c
>> +++ b/fs/ext2/balloc.c
>> @@ -1432,8 +1432,14 @@ ext2_fsblk_t ext2_new_blocks(struct inode *inode, ext2_fsblk_t goal,
>>   ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
>>   {
>>   	unsigned long count = 1;
>> +	struct ext2_inode_info *ei = EXT2_I(inode);
>> +	ext2_fsblk_t ret;
>> +
>> +	mutex_lock(&ei->truncate_mutex);
>> +	ret = ext2_new_blocks(inode, goal, &count, errp);
>> +	mutex_unlock(&ei->truncate_mutex);
>>   
>> -	return ext2_new_blocks(inode, goal, &count, errp);
>> +	return ret;
>>   }
>>   
>>   #ifdef EXT2FS_DEBUG
>> -- 
>> 2.31.1
>>
diff mbox series

Patch

diff --git a/fs/ext2/balloc.c b/fs/ext2/balloc.c
index c8049c90323d..039f655febfd 100644
--- a/fs/ext2/balloc.c
+++ b/fs/ext2/balloc.c
@@ -1432,8 +1432,14 @@  ext2_fsblk_t ext2_new_blocks(struct inode *inode, ext2_fsblk_t goal,
 ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
 {
 	unsigned long count = 1;
+	struct ext2_inode_info *ei = EXT2_I(inode);
+	ext2_fsblk_t ret;
+
+	mutex_lock(&ei->truncate_mutex);
+	ret = ext2_new_blocks(inode, goal, &count, errp);
+	mutex_unlock(&ei->truncate_mutex);
 
-	return ext2_new_blocks(inode, goal, &count, errp);
+	return ret;
 }
 
 #ifdef EXT2FS_DEBUG