From: Michael Bommarito Date: Fri, 17 Apr 2026 22:57:12 +0000 (-0400) Subject: ntfs3: validate split-point offset in indx_insert_into_buffer X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=f1df9d771df47aa40de6d70949c28720ae1e430d;p=thirdparty%2Fkernel%2Flinux.git ntfs3: validate split-point offset in indx_insert_into_buffer indx_insert_into_buffer() computes used = used1 - to_copy - sp_size; memmove(de_t, Add2Ptr(sp, sp_size), used - le32_to_cpu(hdr1->de_off)); where sp and sp_size come from hdr_find_split(). hdr_find_split() walks entries by le16_to_cpu(e->size) without validating that each step stays within hdr->used or that the size field is at least sizeof(struct NTFS_DE). index_hdr_check(), the on-load gatekeeper, only validates header-level fields (used, total, de_off) and does not walk per-entry sizes. A crafted NTFS image whose leaf INDEX_HDR reports used == total but contains one interior NTFS_DE with size = 0xFFF0 therefore passes validation, descends to indx_insert_into_buffer() through the ntfs_create() -> indx_insert_entry() path, and makes hdr_find_split() return an sp whose sp_size (0xFFF0) greatly exceeds the remaining bytes in the buffer. The u32 subtraction underflows and the memmove count becomes a near-4-GiB value, producing an out-of-bounds kernel write that corrupts adjacent allocations and panics the kernel. Reproduced on 7.0.0-rc7 with UML + KASAN via a crafted image and a single 'touch' inside the mounted directory; crash site resolves to fs/ntfs3/index.c at the memmove. Trigger requires only local mount of an attacker-supplied filesystem image (USB, loopback, or removable media auto-mount). Reject the split whenever the chosen sp plus its declared size already extends past hdr1->used. This is the minimal fix; it preserves the existing hdr_find_split() contract and relies on the same out: cleanup path as the pre-existing error returns. A prior OOB read in the very same indx_insert_into_buffer() memmove was fixed in commit b8c44949044e ("fs/ntfs3: Fix OOB read in indx_insert_into_buffer") by tightening hdr_find_e(), but that fix does not cover the split-point size field path addressed here: sp is returned by hdr_find_split(), not hdr_find_e(), and the underflow is driven by sp->size rather than hdr->used exceeding hdr->total. Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block") Cc: stable@vger.kernel.org Reported-by: Michael Bommarito Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito Signed-off-by: Konstantin Komarov --- diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c index 5868964e129c..ade276225999 100644 --- a/fs/ntfs3/index.c +++ b/fs/ntfs3/index.c @@ -1862,6 +1862,20 @@ indx_insert_into_buffer(struct ntfs_index *indx, struct ntfs_inode *ni, memcpy(up_e, sp, sp_size); used1 = le32_to_cpu(hdr1->used); + + /* + * hdr_find_split does not validate per-entry sizes, so a crafted + * NTFS_DE whose le16 size field is out of range can place sp such + * that (PtrOffset(hdr1, sp) + sp_size) exceeds used1. Without this + * guard the u32 'used = used1 - to_copy - sp_size' underflows and + * the subsequent memmove count becomes a near-4-GiB value, + * triggering an out-of-bounds kernel write. + */ + if (PtrOffset(hdr1, sp) + sp_size > used1) { + err = -EINVAL; + goto out; + } + hdr1_saved = kmemdup(hdr1, used1, GFP_NOFS); if (!hdr1_saved) { err = -ENOMEM;