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[68.48.65.54]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7bd7d849afesm165696547b3.49.2026.05.13.09.27.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 13 May 2026 09:27:01 -0700 (PDT) From: Michael Bommarito To: Trond Myklebust , Anna Schumaker Cc: Jonathan Curley , Tigran Mkrtchyan , Kees Cook , Jeff Layton , Mike Snitzer , Tom Haynes , Weston Andros Adamson , Tao Peng , linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH] NFSv4/flexfiles: reject zero filehandle version count Date: Wed, 13 May 2026 12:26:56 -0400 Message-ID: <20260513162656.1896434-1-michael.bommarito@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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 =3D=3D 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=3D1 regression still opens, reads, and unmounts cleanl= y. Cc: stable@vger.kernel.org Fixes: d67ae825a59d ("pnfs/flexfiles: Add the FlexFile Layout Driver") Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Michael Bommarito --- fs/nfs/flexfilelayout/flexfilelayout.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/nfs/flexfilelayout/flexfilelayout.c b/fs/nfs/flexfilelayout= /flexfilelayout.c index 8b1559171fe3..e22a8e0daf2c 100644 --- a/fs/nfs/flexfilelayout/flexfilelayout.c +++ b/fs/nfs/flexfilelayout/flexfilelayout.c @@ -551,6 +551,10 @@ ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh, if (!p) goto out_err_free; fh_count =3D be32_to_cpup(p); + if (fh_count =3D=3D 0) { + rc =3D -EINVAL; + goto out_err_free; + } =20 dss_info->fh_versions =3D kzalloc_objs(struct nfs_fh, fh_count, gfp_flags); --=20 2.53.0