FAILED: patch "[PATCH] NFSv4/flexfiles: reject zero filehandle version count" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026070243-trimness-trickle-088e@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2 Mon Sep 17 00:00:00 2001
From: Michael Bommarito <[email protected]>
Date: Wed, 13 May 2026 12:26:56 -0400
Subject: [PATCH] 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.

index 6a84d85e0651..99caa8d28c25 100644
@@ -551,6 +551,10 @@ ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
 			if (!p)
 				goto out_err_free;
 			fh_count = be32_to_cpup(p);
+			if (fh_count == 0) {
+				rc = -EINVAL;
+				goto out_err_free;
+			}
 
 			dss_info->fh_versions =
 			    kzalloc_objs(struct nfs_fh, fh_count, gfp_flags);

From: Michael Bommarito <[email protected]>

[ Upstream commit 2c6bb3c40bc24f6aa8dfbe6fe98c3ad6389203f2 ]

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.

---
 fs/nfs/flexfilelayout/flexfilelayout.c | 4 ++++
 1 file changed, 4 insertions(+)

index 42c73c647a27fe..98536d2dad5e1f 100644
@@ -460,6 +460,10 @@ ff_layout_alloc_lseg(struct pnfs_layout_hdr *lh,
 		if (!p)
 			goto out_err_free;
 		fh_count = be32_to_cpup(p);
+		if (fh_count == 0) {
+			rc = -EINVAL;
+			goto out_err_free;
+		}
 
 		fls->mirror_array[i]->fh_versions =
 			kcalloc(fh_count, sizeof(struct nfs_fh),

2.53.0