ntfs3: validate split-point offset in indx_insert_into_buffer

Overview

In the Linux kernel, the following vulnerability has been resolved:

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.

Affected

• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 8e4ba5a38c155bb3c1c11e63cd285b178cdb099e
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 4c2f648139a0a86f4486170f72e24fedd4fae74e
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < b232eb5c9fe11ec2368e9b565db69c724c35fbd2
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 7bf74e6baf810fe325f111996496c678fc6e244f
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < f3624cc069195001c88df7a291af215f2133ff2c
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < 1758a564b6ebe7f4a82f23c9851d1cae15549457
• Linux >= 82cae269cfa953032fbb8980a7d554d60fb00b17 < f1df9d771df47aa40de6d70949c28720ae1e430d
• Linux 5.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.