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.
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 <michael.bommarito@gmail.com>
---
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 = 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);
--
2.53.0