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Message-ID: <20240703092953.j53in72xzn4vheca@quack3>
Date: Wed, 3 Jul 2024 11:29:53 +0200
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
jack@...e.cz, ritesh.list@...il.com, linux-kernel@...r.kernel.org,
yi.zhang@...wei.com, yangerkun@...wei.com,
Baokun Li <libaokun1@...wei.com>,
syzbot+ae688d469e36fb5138d0@...kaller.appspotmail.com,
stable@...nel.org
Subject: Re: [PATCH 1/2] ext4: check dot and dotdot of dx_root before making
dir indexed
On Tue 02-07-24 21:23:48, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
>
> Syzbot reports a issue as follows:
> ============================================
> BUG: unable to handle page fault for address: ffffed11022e24fe
> PGD 23ffee067 P4D 23ffee067 PUD 0
> Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
> CPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0
> Call Trace:
> <TASK>
> make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341
> ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451
> ext4_rename fs/ext4/namei.c:3936 [inline]
> ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214
> [...]
> ============================================
>
> The immediate cause of this problem is that there is only one valid dentry
> for the block to be split during do_split, so split==0 results in out of
> bounds accesses to the map triggering the issue.
>
> do_split
> unsigned split
> dx_make_map
> count = 1
> split = count/2 = 0;
> continued = hash2 == map[split - 1].hash;
> ---> map[4294967295]
>
> The maximum length of a filename is 255 and the minimum block size is 1024,
> so it is always guaranteed that the number of entries is greater than or
> equal to 2 when do_split() is called.
>
> But syzbot's crafted image has no dot and dotdot in dir, and the dentry
> distribution in dirblock is as follows:
>
> bus dentry1 hole dentry2 free
> |xx--|xx-------------|...............|xx-------------|...............|
> 0 12 (8+248)=256 268 256 524 (8+256)=264 788 236 1024
>
> So when renaming dentry1 increases its name_len length by 1, neither hole
> nor free is sufficient to hold the new dentry, and make_indexed_dir() is
> called.
>
> In make_indexed_dir() it is assumed that the first two entries of the
> dirblock must be dot and dotdot, so bus and dentry1 are left in dx_root
> because they are treated as dot and dotdot, and only dentry2 is moved
> to the new leaf block. That's why count is equal to 1.
>
> Therefore add the ext4_check_dx_root() helper function to add more sanity
> checks to dot and dotdot before starting the conversion to avoid the above
> issue.
>
> Reported-by: syzbot+ae688d469e36fb5138d0@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0
> Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
> Cc: stable@...nel.org
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
Thanks! The patch looks good to me. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> fs/ext4/namei.c | 56 ++++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 51 insertions(+), 5 deletions(-)
>
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index e6769b97a970..35881e3dd880 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -2172,6 +2172,52 @@ static int add_dirent_to_buf(handle_t *handle, struct ext4_filename *fname,
> return err ? err : err2;
> }
>
> +static bool ext4_check_dx_root(struct inode *dir, struct dx_root *root)
> +{
> + struct fake_dirent *fde;
> + const char *error_msg;
> + unsigned int rlen;
> + unsigned int blocksize = dir->i_sb->s_blocksize;
> + char *blockend = (char *)root + dir->i_sb->s_blocksize;
> +
> + fde = &root->dot;
> + if (unlikely(fde->name_len != 1)) {
> + error_msg = "invalid name_len for '.'";
> + goto corrupted;
> + }
> + if (unlikely(strncmp(root->dot_name, ".", fde->name_len))) {
> + error_msg = "invalid name for '.'";
> + goto corrupted;
> + }
> + rlen = ext4_rec_len_from_disk(fde->rec_len, blocksize);
> + if (unlikely((char *)fde + rlen >= blockend)) {
> + error_msg = "invalid rec_len for '.'";
> + goto corrupted;
> + }
> +
> + fde = &root->dotdot;
> + if (unlikely(fde->name_len != 2)) {
> + error_msg = "invalid name_len for '..'";
> + goto corrupted;
> + }
> + if (unlikely(strncmp(root->dotdot_name, "..", fde->name_len))) {
> + error_msg = "invalid name for '..'";
> + goto corrupted;
> + }
> + rlen = ext4_rec_len_from_disk(fde->rec_len, blocksize);
> + if (unlikely((char *)fde + rlen >= blockend)) {
> + error_msg = "invalid rec_len for '..'";
> + goto corrupted;
> + }
> +
> + return true;
> +
> +corrupted:
> + EXT4_ERROR_INODE(dir, "Corrupt dir, %s, running e2fsck is recommended",
> + error_msg);
> + return false;
> +}
> +
> /*
> * This converts a one block unindexed directory to a 3 block indexed
> * directory, and adds the dentry to the indexed directory.
> @@ -2206,17 +2252,17 @@ static int make_indexed_dir(handle_t *handle, struct ext4_filename *fname,
> brelse(bh);
> return retval;
> }
> +
> root = (struct dx_root *) bh->b_data;
> + if (!ext4_check_dx_root(dir, root)) {
> + brelse(bh);
> + return -EFSCORRUPTED;
> + }
>
> /* The 0th block becomes the root, move the dirents out */
> fde = &root->dotdot;
> de = (struct ext4_dir_entry_2 *)((char *)fde +
> ext4_rec_len_from_disk(fde->rec_len, blocksize));
> - if ((char *) de >= (((char *) root) + blocksize)) {
> - EXT4_ERROR_INODE(dir, "invalid rec_len for '..'");
> - brelse(bh);
> - return -EFSCORRUPTED;
> - }
> len = ((char *) root) + (blocksize - csum_size) - (char *) de;
>
> /* Allocate new block for the 0th block's dirents */
> --
> 2.39.2
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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