From 6098790c403d5e95a35bb6bf938591ca8c8e224f Mon Sep 17 00:00:00 2001 From: DaeMyung Kang Date: Sat, 9 May 2026 15:12:35 +0900 Subject: [PATCH] ntfs: validate MFT attrs_offset against bytes_in_use ntfs_mft_record_check() verifies that attrs_offset is aligned and that the resulting pointer stays within the allocated MFT record buffer, but it does not check that the first attribute header starts within the bytes_in_use area. A malformed record with attrs_offset greater than bytes_in_use can pass this check as long as attrs_offset is still within bytes_allocated. The attribute parser then computes the remaining record space by subtracting the attribute pointer from bytes_in_use. Because that value is unsigned, the subtraction can underflow and allow bytes after bytes_in_use to be interpreted as an attribute. Reject records where attrs_offset is outside bytes_in_use or where the used area does not even contain the four-byte attribute type/AT_END terminator at attrs_offset. A small userspace model with attrs_offset=128 and bytes_in_use=64 shows the current check accepts the record and the parser space calculation underflows to 0xffffffc0. With this change the same malformed record is rejected before the attribute walker is entered. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: DaeMyung Kang Signed-off-by: Namjae Jeon --- fs/ntfs/mft.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c index 68f6fc8b7b62..729b259974eb 100644 --- a/fs/ntfs/mft.c +++ b/fs/ntfs/mft.c @@ -30,6 +30,8 @@ int ntfs_mft_record_check(const struct ntfs_volume *vol, struct mft_record *m, { struct attr_record *a; struct super_block *sb = vol->sb; + u16 attrs_offset; + u32 bytes_in_use; if (!ntfs_is_file_record(m->magic)) { ntfs_error(sb, "Record %llu has no FILE magic (0x%x)\n", @@ -65,7 +67,16 @@ int ntfs_mft_record_check(const struct ntfs_volume *vol, struct mft_record *m, goto err_out; } - a = (struct attr_record *)((char *)m + le16_to_cpu(m->attrs_offset)); + attrs_offset = le16_to_cpu(m->attrs_offset); + bytes_in_use = le32_to_cpu(m->bytes_in_use); + + if (attrs_offset > bytes_in_use || + bytes_in_use - attrs_offset < sizeof_field(struct attr_record, type)) { + ntfs_error(sb, "Record %llu has corrupt attribute offset\n", mft_no); + goto err_out; + } + + a = (struct attr_record *)((char *)m + attrs_offset); if ((char *)a < (char *)m || (char *)a > (char *)m + vol->mft_record_size) { ntfs_error(sb, "Record %llu is corrupt\n", mft_no); goto err_out;