From: Baokun Li libaokun1@huawei.com

stable inclusion from stable-v5.10.224 commit 42d420517072028fb0eb852c358056b7717ba5aa category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAKQB7 CVE: CVE-2024-42304

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...

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commit 50ea741def587a64e08879ce6c6a30131f7111e7 upstream.

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@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0 Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3") Cc: stable@kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com Reviewed-by: Jan Kara jack@suse.cz Link: https://patch.msgid.link/20240702132349.2600605-2-libaokun@huaweicloud.com Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yifan Qiao qiaoyifan4@huawei.com --- 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 4f1db44acd1c..d009142386a1 100644 --- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -2126,6 +2126,52 @@ 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. @@ -2159,17 +2205,17 @@ 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 */