From: Eric Biggers <ebiggers@kernel.org>
To: Tudor Ambarus <tudor.ambarus@linaro.org>
Cc: tytso@mit.edu, adilger.kernel@dilger.ca,
linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
joneslee@google.com,
syzbot+0827b4b52b5ebf65f219@syzkaller.appspotmail.com,
stable@vger.kernel.org
Subject: Re: [PATCH v2] ext4: Fix possible use-after-free in ext4_find_extent
Date: Thu, 29 Dec 2022 22:56:16 -0800 [thread overview]
Message-ID: <Y66LkPumQjHC2U7d@sol.localdomain> (raw)
In-Reply-To: <20221230062931.2344157-1-tudor.ambarus@linaro.org>
On Fri, Dec 30, 2022 at 08:29:31AM +0200, Tudor Ambarus wrote:
> syzbot reported a use-after-free Read in ext4_find_extent that is hit when
> using a corrupted file system. The bug was reported on Android 5.15, but
> using the same reproducer triggers the bug on v6.2-rc1 as well.
>
> Fix the use-after-free by checking the extent header magic. An alternative
> would be to check the values of EXT4_{FIRST,LAST}_{EXTENT,INDEX} used in
> ext4_ext_binsearch() and ext4_ext_binsearch_idx(), so that we make sure
> that pointers returned by EXT4_{FIRST,LAST}_{EXTENT,INDEX} don't exceed the
> bounds of the extent tree node. But this alternative will not squash
> the bug for the cases where eh->eh_entries fit into eh->eh_max. We could
> also try to check the sanity of the path, but costs more than checking just
> the header magic, so stick to the header magic sanity check.
>
> Link: https://syzkaller.appspot.com/bug?id=be6e90ce70987950e6deb3bac8418344ca8b96cd
> Reported-by: syzbot+0827b4b52b5ebf65f219@syzkaller.appspotmail.com
> Cc: stable@vger.kernel.org
> Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> ---
> v2: drop wrong/uneeded le16_to_cpu() conversion for eh->eh_magic
>
> fs/ext4/extents.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 9de1c9d1a13d..bedc8c098449 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -894,6 +894,12 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
> gfp_flags |= __GFP_NOFAIL;
>
> eh = ext_inode_hdr(inode);
> + if (eh->eh_magic != EXT4_EXT_MAGIC) {
> + EXT4_ERROR_INODE(inode, "Extent header has invalid magic.");
> + ret = -EFSCORRUPTED;
> + goto err;
> + }
> +
This is (incompletely) validating the extent header in the inode. Isn't that
supposed to happen when the inode is loaded? See how __ext4_iget() calls
ext4_ext_check_inode(). Why isn't that working here?
- Eric
next prev parent reply other threads:[~2022-12-30 6:56 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-30 6:29 [PATCH v2] ext4: Fix possible use-after-free in ext4_find_extent Tudor Ambarus
2022-12-30 6:56 ` Eric Biggers [this message]
2022-12-30 11:42 ` Tudor Ambarus
2022-12-30 20:07 ` Eric Biggers
2023-01-02 5:41 ` Tudor Ambarus
2022-12-30 20:22 ` Theodore Ts'o
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y66LkPumQjHC2U7d@sol.localdomain \
--to=ebiggers@kernel.org \
--cc=adilger.kernel@dilger.ca \
--cc=joneslee@google.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=stable@vger.kernel.org \
--cc=syzbot+0827b4b52b5ebf65f219@syzkaller.appspotmail.com \
--cc=tudor.ambarus@linaro.org \
--cc=tytso@mit.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox