From: Baokun Li <libaokun1@xxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=ae688d469e36fb5138d0
Fixes: ac27a0ec112a ("[PATCH] ext4: initial copy of files from ext3")
Cc: stable@xxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
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
