CVE-2026-53392NFSv4/flexfiles: reject zero filehandle version count

Official description

In the Linux kernel, the following vulnerability has been resolved: NFSv4/flexfiles: reject zero filehandle version count ff_layout_alloc_lseg() decodes the filehandle-version array count from the flexfiles layout body. The value is used as the count for kzalloc_objs(), and the current code only rejects NULL. A zero count yields ZERO_SIZE_PTR, which can be stored in dss_info->fh_versions even though later flexfiles paths assume that at least one filehandle version exists. Reject fh_count == 0 before the allocation, matching the existing zero version_count validation in the flexfiles GETDEVICEINFO parser. A QEMU/KASAN run with a malformed flexfiles layout hit: KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:ff_layout_encode_ff_layoutupdate.isra.0+0x15f/0x750 ff_layout_encode_layoutreturn+0x683/0x970 nfs4_xdr_enc_layoutreturn+0x278/0x3a0 Kernel panic - not syncing: Fatal exception The patched kernel rejects the malformed layout without KASAN/oops/panic, and a valid fh_count=1 regression still opens, reads, and unmounts cleanly.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/9033591535c066726f5b505126ccb4068b98fa4f
• https://git.kernel.org/stable/c/18cc6d57a14fa65ab2a2b52279f549041c4bc9cf
• https://git.kernel.org/stable/c/be7829715e341b42846437dd9e721005db59f0cc
• https://git.kernel.org/stable/c/eeabb9020721db6bc132e68eeae380b8d4fb4b04
• https://git.kernel.org/stable/c/7779c85028a0676fb190cde4f0c540f4f8e97761
• https://git.kernel.org/stable/c/d8c90c7cc061265d5f2813a1f5c82ef2f4707e67
• https://git.kernel.org/stable/c/2131ed64b767ffa8bcdb3677d90f3964e39aabc8
• https://git.kernel.org/stable/c/2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2