The $MFT attribute-list walk in ntfs_read_inode_mount() validates each entry only with "(u8 *)al_entry + 6 > al_end" and "(u8 *)al_entry + le16_to_cpu(al_entry->length) > al_end", but then reads al_entry->lowest_vcn (an __le64 at offset 8) and al_entry->mft_reference (offset 16) -- fields beyond the 6 bytes proven in range. al_entry->length is attacker-controlled and only required non-zero, so a short entry (e.g. length 8) placed at the tail passes both checks while the lowest_vcn / mft_reference reads fall past al_end. al_end is ni->attr_list + attr_list_size (the on-disk size); the buffer is kvzalloc(round_up(attr_list_size, SECTOR_SIZE)), so the sector rounding usually absorbs the over-read -- but when attr_list_size is a multiple of SECTOR_SIZE there is no slack and a crafted $MFT attribute list produces an out-of-bounds read at mount time. Validate the entry with ntfs_attr_list_entry_is_valid() (added in patch 1/3) before dereferencing it, matching the bound the other attribute-list walks now use. The validator already requires the length to cover the fixed header, which makes the separate "!al_entry->length" check redundant, so drop it too. Fixes: 1e9ea7e04472 ("Revert "fs: Remove NTFS classic"") Signed-off-by: Bryam Vargas --- v4: also drop the now-redundant "if (!al_entry->length)" check, per Hyunchul's review -- ntfs_attr_list_entry_is_valid() forces name_offset == sizeof(struct attr_list_entry) and requires name_offset + name_length * sizeof(__le16) <= length, so length == 0 is already rejected there (and length is a multiple of 8, so a valid entry is at least 32 bytes and next_al_entry still advances -- no zero-length loop). Rebased onto the "ntfs: validate attribute values on lookup" series (0001-0004) now applied to ntfs-next; added the Fixes: tag. Compile-tested on ntfs-next. v3 (Hyunchul Lee review): validate with the extracted ntfs_attr_list_entry_is_valid() helper rather than an open-coded bound, matching the other attribute-list walks. v2: dropped the redundant Reported-by; reproducer omitted on the public list (available to the maintainers on request). Sibling of the ntfs_external_attr_find() look-ahead OOB (2/3): the same struct attr_list_entry fixed fields (lowest_vcn at 8, mft_reference at 16) are read here with a weaker bound. Geometry is arch-independent (identical -m32/-m64). fs/ntfs/inode.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c index 8a7798d7f5fc..2f2634baa285 100644 --- a/fs/ntfs/inode.c +++ b/fs/ntfs/inode.c @@ -1997,10 +1997,7 @@ int ntfs_read_inode_mount(struct inode *vi) /* Catch the end of the attribute list. */ if ((u8 *)al_entry == al_end) goto em_put_err_out; - if (!al_entry->length) - goto em_put_err_out; - if ((u8 *)al_entry + 6 > al_end || - (u8 *)al_entry + le16_to_cpu(al_entry->length) > al_end) + if (!ntfs_attr_list_entry_is_valid(al_entry, al_end)) goto em_put_err_out; next_al_entry = (struct attr_list_entry *)((u8 *)al_entry + le16_to_cpu(al_entry->length)); -- 2.43.0