* [PATCH] ext2: fix potential use after free
@ 2018-11-25 0:58 Pan Bian
2018-11-27 9:19 ` Jan Kara
0 siblings, 1 reply; 2+ messages in thread
From: Pan Bian @ 2018-11-25 0:58 UTC (permalink / raw)
To: Jan Kara; +Cc: linux-ext4, linux-kernel, Pan Bian
The function ext2_xattr_set calls brelse(bh) to drop the reference count
of bh. After that, bh may be freed. However, following brelse(bh),
it reads bh->b_data via macro HDR(bh). This may result in a
use-after-free bug. This patch moves brelse(bh) after reading field.
Signed-off-by: Pan Bian <bianpan2016@163.com>
---
fs/ext2/xattr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
index 62d9a659a..dd8f10d 100644
--- a/fs/ext2/xattr.c
+++ b/fs/ext2/xattr.c
@@ -612,9 +612,9 @@ bad_block: ext2_error(sb, "ext2_xattr_set",
}
cleanup:
- brelse(bh);
if (!(bh && header == HDR(bh)))
kfree(header);
+ brelse(bh);
up_write(&EXT2_I(inode)->xattr_sem);
return error;
--
2.7.4
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] ext2: fix potential use after free
2018-11-25 0:58 [PATCH] ext2: fix potential use after free Pan Bian
@ 2018-11-27 9:19 ` Jan Kara
0 siblings, 0 replies; 2+ messages in thread
From: Jan Kara @ 2018-11-27 9:19 UTC (permalink / raw)
To: Pan Bian; +Cc: Jan Kara, linux-ext4, linux-kernel
On Sun 25-11-18 08:58:02, Pan Bian wrote:
> The function ext2_xattr_set calls brelse(bh) to drop the reference count
> of bh. After that, bh may be freed. However, following brelse(bh),
> it reads bh->b_data via macro HDR(bh). This may result in a
> use-after-free bug. This patch moves brelse(bh) after reading field.
>
> Signed-off-by: Pan Bian <bianpan2016@163.com>
Thanks for the fix! I've added the patch to my tree.
Honza
> ---
> fs/ext2/xattr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/ext2/xattr.c b/fs/ext2/xattr.c
> index 62d9a659a..dd8f10d 100644
> --- a/fs/ext2/xattr.c
> +++ b/fs/ext2/xattr.c
> @@ -612,9 +612,9 @@ bad_block: ext2_error(sb, "ext2_xattr_set",
> }
>
> cleanup:
> - brelse(bh);
> if (!(bh && header == HDR(bh)))
> kfree(header);
> + brelse(bh);
> up_write(&EXT2_I(inode)->xattr_sem);
>
> return error;
> --
> 2.7.4
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
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