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=be6e90ce70987950e6deb3bac8418344ca8b96c... 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