[PATCH v2] ext4: fix error pointer dereference

[PATCH v2] ext4: fix error pointer dereference

[Jeffle Xu]

Don't pass error pointers to brelse().

commit 7159a986b420 ("ext4: fix some error pointer dereferences") has fixed
some cases, fix the remaining one case.

Once ext4_xattr_block_find()->ext4_sb_bread() failed, error pointer is
stored in @bs->bh, which will be passed to brelse() in the cleanup
routine of ext4_xattr_set_handle(). This will then cause a NULL panic
crash in __brelse().

BUG: unable to handle kernel NULL pointer dereference at 000000000000005b
RIP: 0010:__brelse+0x1b/0x50
Call Trace:
 ext4_xattr_set_handle+0x163/0x5d0
 ext4_xattr_set+0x95/0x110
 __vfs_setxattr+0x6b/0x80
 __vfs_setxattr_noperm+0x68/0x1b0
 vfs_setxattr+0xa0/0xb0
 setxattr+0x12c/0x1a0
 path_setxattr+0x8d/0xc0
 __x64_sys_setxattr+0x27/0x30
 do_syscall_64+0x60/0x250
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

In this case, @bs->bh stores '-EIO' actually.

Fixes: fb265c9cb49e ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: stable@kernel.org # 2.6.19
---
 fs/ext4/xattr.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 21df43a..01ba663 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1800,8 +1800,11 @@ struct ext4_xattr_block_find {
 	if (EXT4_I(inode)->i_file_acl) {
 		/* The inode already has an extended attribute block. */
 		bs->bh = ext4_sb_bread(sb, EXT4_I(inode)->i_file_acl, REQ_PRIO);
-		if (IS_ERR(bs->bh))
-			return PTR_ERR(bs->bh);
+		if (IS_ERR(bs->bh)) {
+			error = PTR_ERR(bs->bh);
+			bs->bh = NULL;
+			return error;
+		}
 		ea_bdebug(bs->bh, "b_count=%d, refcount=%d",
 			atomic_read(&(bs->bh->b_count)),
 			le32_to_cpu(BHDR(bs->bh)->h_refcount));
-- 
1.8.3.1

Re: [PATCH v2] ext4: fix error pointer dereference

[Ritesh Harjani]

On 4/23/20 1:16 PM, Jeffle Xu wrote:
> Don't pass error pointers to brelse().
> 
> commit 7159a986b420 ("ext4: fix some error pointer dereferences") has fixed
> some cases, fix the remaining one case.
> 
> Once ext4_xattr_block_find()->ext4_sb_bread() failed, error pointer is
> stored in @bs->bh, which will be passed to brelse() in the cleanup
> routine of ext4_xattr_set_handle(). This will then cause a NULL panic
> crash in __brelse().
> 
> BUG: unable to handle kernel NULL pointer dereference at 000000000000005b
> RIP: 0010:__brelse+0x1b/0x50
> Call Trace:
>   ext4_xattr_set_handle+0x163/0x5d0
>   ext4_xattr_set+0x95/0x110
>   __vfs_setxattr+0x6b/0x80
>   __vfs_setxattr_noperm+0x68/0x1b0
>   vfs_setxattr+0xa0/0xb0
>   setxattr+0x12c/0x1a0
>   path_setxattr+0x8d/0xc0
>   __x64_sys_setxattr+0x27/0x30
>   do_syscall_64+0x60/0x250
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> In this case, @bs->bh stores '-EIO' actually.
> 
> Fixes: fb265c9cb49e ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> Cc: stable@kernel.org # 2.6.19

Thanks for your patch. Looks good to me.
Feel free to add:

Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>

> ---
>   fs/ext4/xattr.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 21df43a..01ba663 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1800,8 +1800,11 @@ struct ext4_xattr_block_find {
>   	if (EXT4_I(inode)->i_file_acl) {
>   		/* The inode already has an extended attribute block. */
>   		bs->bh = ext4_sb_bread(sb, EXT4_I(inode)->i_file_acl, REQ_PRIO);
> -		if (IS_ERR(bs->bh))
> -			return PTR_ERR(bs->bh);
> +		if (IS_ERR(bs->bh)) {
> +			error = PTR_ERR(bs->bh);
> +			bs->bh = NULL;
> +			return error;
> +		}
>   		ea_bdebug(bs->bh, "b_count=%d, refcount=%d",
>   			atomic_read(&(bs->bh->b_count)),
>   			le32_to_cpu(BHDR(bs->bh)->h_refcount));
> 

Re: [PATCH v2] ext4: fix error pointer dereference

[Jan Kara]

On Thu 23-04-20 15:46:44, Jeffle Xu wrote:
> Don't pass error pointers to brelse().
> 
> commit 7159a986b420 ("ext4: fix some error pointer dereferences") has fixed
> some cases, fix the remaining one case.
> 
> Once ext4_xattr_block_find()->ext4_sb_bread() failed, error pointer is
> stored in @bs->bh, which will be passed to brelse() in the cleanup
> routine of ext4_xattr_set_handle(). This will then cause a NULL panic
> crash in __brelse().
> 
> BUG: unable to handle kernel NULL pointer dereference at 000000000000005b
> RIP: 0010:__brelse+0x1b/0x50
> Call Trace:
>  ext4_xattr_set_handle+0x163/0x5d0
>  ext4_xattr_set+0x95/0x110
>  __vfs_setxattr+0x6b/0x80
>  __vfs_setxattr_noperm+0x68/0x1b0
>  vfs_setxattr+0xa0/0xb0
>  setxattr+0x12c/0x1a0
>  path_setxattr+0x8d/0xc0
>  __x64_sys_setxattr+0x27/0x30
>  do_syscall_64+0x60/0x250
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> In this case, @bs->bh stores '-EIO' actually.
> 
> Fixes: fb265c9cb49e ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> Cc: stable@kernel.org # 2.6.19

Thanks for the patch! It looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

									Honza

> ---
>  fs/ext4/xattr.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 21df43a..01ba663 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1800,8 +1800,11 @@ struct ext4_xattr_block_find {
>  	if (EXT4_I(inode)->i_file_acl) {
>  		/* The inode already has an extended attribute block. */
>  		bs->bh = ext4_sb_bread(sb, EXT4_I(inode)->i_file_acl, REQ_PRIO);
> -		if (IS_ERR(bs->bh))
> -			return PTR_ERR(bs->bh);
> +		if (IS_ERR(bs->bh)) {
> +			error = PTR_ERR(bs->bh);
> +			bs->bh = NULL;
> +			return error;
> +		}
>  		ea_bdebug(bs->bh, "b_count=%d, refcount=%d",
>  			atomic_read(&(bs->bh->b_count)),
>  			le32_to_cpu(BHDR(bs->bh)->h_refcount));
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH v2] ext4: fix error pointer dereference

[Theodore Y. Ts'o]

On Thu, Apr 23, 2020 at 03:46:44PM +0800, Jeffle Xu wrote:
> Don't pass error pointers to brelse().
> 
> commit 7159a986b420 ("ext4: fix some error pointer dereferences") has fixed
> some cases, fix the remaining one case.
> 
> Once ext4_xattr_block_find()->ext4_sb_bread() failed, error pointer is
> stored in @bs->bh, which will be passed to brelse() in the cleanup
> routine of ext4_xattr_set_handle(). This will then cause a NULL panic
> crash in __brelse().
> 
> BUG: unable to handle kernel NULL pointer dereference at 000000000000005b
> RIP: 0010:__brelse+0x1b/0x50
> Call Trace:
>  ext4_xattr_set_handle+0x163/0x5d0
>  ext4_xattr_set+0x95/0x110
>  __vfs_setxattr+0x6b/0x80
>  __vfs_setxattr_noperm+0x68/0x1b0
>  vfs_setxattr+0xa0/0xb0
>  setxattr+0x12c/0x1a0
>  path_setxattr+0x8d/0xc0
>  __x64_sys_setxattr+0x27/0x30
>  do_syscall_64+0x60/0x250
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> 
> In this case, @bs->bh stores '-EIO' actually.
> 
> Fixes: fb265c9cb49e ("ext4: add ext4_sb_bread() to disambiguate ENOMEM cases")
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
> Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> Cc: stable@kernel.org # 2.6.19
> Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
> Reviewed-by: Jan Kara <jack@suse.cz>

Applied, thanks.

						- Ted