indx_insert_into_root() promotes a full resident $INDEX_ROOT into $INDEX_ALLOCATION and copies all non-last resident root entries into a newly allocated INDEX_BUFFER via hdr_insert_head(). The source byte count 'to_move' is summed from the on-disk resident entry sizes and is independent of the destination buffer size, which comes from root->index_block_size (via indx->index_bits). A crafted NTFS image that keeps a valid, full resident root but shrinks root->index_block_size down to 512 after the root has been populated makes hdr_insert_head() memcpy attacker-controlled resident entry bytes past the end of the kmalloc(1u << indx->index_bits) allocation returned by indx_new(). For a 512-byte destination and a resident root whose non-last entries total 560 bytes, the memcpy overruns by 120 bytes and a following memmove extends the highest written offset to 136 bytes past the allocation. The overflow bytes are a direct copy of on-disk entries (via kmemdup), so they are fully attacker-controlled. The write is reachable from unprivileged open(O_CREAT) on a mounted crafted NTFS image: a single sufficiently long create in a directory whose resident root is already full forces root promotion and triggers the copy. This is a controlled out-of-bounds write of 120-136 bytes past a kmalloc(index_block_size) allocation, with attacker-controlled content. It is a bounded adjacent-heap corruption primitive; it is not an arbitrary-address write. Successful exploitation into a named victim object depends on the surrounding slab layout. Reject the copy at the sink. The destination's INDEX_HDR already reports hdr_total (the payload capacity of the new buffer) and hdr_used (the bytes already consumed by the terminal END entry installed by indx_new()); require that to_move fits in the remaining payload before calling hdr_insert_head(). On mismatch, fail with -EINVAL and mark the filesystem as having a detected on-disk inconsistency, which is the same behaviour as the surrounding validation in this function. Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito --- - FYI, like the sp_size patch, I have a larger refactor that might make this easier to avoid long term. It's a mount-time variant that adds the cross-check between root->index_block_size and the resident root attribute size to indx_init() instead of the sink, closing the whole "root entries do not fit declared index_block_size" class for any future caller that reaches hdr_insert_head from elsewhere. Happy to send it as v2 if you prefer the wider change; otherwise, this minimal guard is scoped to the minimal memcpy overrun site and is easier to backport. fs/ntfs3/index.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c index 2c43e7c27861..b7633b721d19 100644 --- a/fs/ntfs3/index.c +++ b/fs/ntfs3/index.c @@ -1740,6 +1740,22 @@ static int indx_insert_into_root(struct ntfs_index *indx, struct ntfs_inode *ni, hdr_used = le32_to_cpu(hdr->used); hdr_total = le32_to_cpu(hdr->total); + /* + * The destination INDEX_BUFFER has 'hdr_total' bytes of payload + * available after the header, of which 'hdr_used' are already + * consumed by the single terminal END entry installed by + * indx_new(). A crafted image can present a resident root whose + * non-last entries (summing to 'to_move') exceed what fits in + * this buffer; copying them unchecked would overrun the + * kmalloc(1u << indx->index_bits) allocation backing the new + * buffer. Reject the copy in that case. + */ + if (to_move > hdr_total - hdr_used) { + err = -EINVAL; + ntfs_set_state(sbi, NTFS_DIRTY_ERROR); + goto out_put_n; + } + /* Copy root entries into new buffer. */ hdr_insert_head(hdr, re, to_move); -- 2.53.0