linux-ext4 - Re: [PATCH] ext4: fix error pointer dereference

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Date:   Thu, 23 Apr 2020 15:38:03 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     tytso@....edu, jack@...e.cz
Cc:     linux-ext4@...r.kernel.org, joseph.qi@...ux.alibaba.com
Subject: Re: [PATCH] ext4: fix error pointer dereference

Please ignore this patch since there's a bug in this patch. Sorry for that.

On 4/23/20 3:27 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@...ux.alibaba.com>
> Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> Cc: stable@...nel.org # 2.6.19
> ---
>   fs/ext4/xattr.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 21df43a..c0ebd0f 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -1800,8 +1800,10 @@ 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))
> +		if (IS_ERR(bs->bh)) {
> +			bs->bh = NULL;
>   			return PTR_ERR(bs->bh);
> +		}
>   		ea_bdebug(bs->bh, "b_count=%d, refcount=%d",
>   			atomic_read(&(bs->bh->b_count)),
>   			le32_to_cpu(BHDR(bs->bh)->h_refcount));