In the Linux kernel, the following vulnerability has been resolved:
ext4: detect invalid INLINE_DATA + EXTENTS flag combination
syzbot reported a BUG_ON in ext4_es_cache_extent() when opening a verity
file on a corrupted ext4 filesystem mounted without a journal.
The issue is that the filesystem has an inode with both the INLINE_DATA
and EXTENTS flags set:
EXT4-fs error (device loop0): ext4_cache_extents:545: inode #15:
comm syz.0.17: corrupted extent tree: lblk 0 < prev 66
Investigation revealed that the inode has both flags set:
DEBUG: inode 15 - flag=1, i_inline_off=164, has_inline=1, extents_flag=1
This is an invalid combination since an inode should have either:
- INLINE_DATA: data stored directly in the inode
- EXTENTS: data stored in extent-mapped blocks
Having both flags causes ext4_has_inline_data() to return true, skipping
extent tree validation in __ext4_iget(). The unvalidated out-of-order
extents then trigger a BUG_ON in ext4_es_cache_extent() due to integer
underflow when calculating hole sizes.
Fix this by detecting this invalid flag combination early in ext4_iget()
and rejecting the corrupted inode.
