* [PATCH v2 1/2] NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr
2026-05-27 16:30 [PATCH v2 0/2] NFSv4/pNFS: fix client kernel panic from malformed GETDEVICEINFO Michael Bommarito
@ 2026-05-27 16:30 ` Michael Bommarito
2026-05-27 16:30 ` [PATCH v2 2/2] NFSv4/flexfile,filelayout: bound multipath DS count in GETDEVICEINFO Michael Bommarito
1 sibling, 0 replies; 3+ messages in thread
From: Michael Bommarito @ 2026-05-27 16:30 UTC (permalink / raw)
To: Trond Myklebust, Anna Schumaker
Cc: Jeff Layton, Tom Haynes, Peng Tao, Kees Cook, Mike Snitzer,
Tigran Mkrtchyan, linux-nfs, linux-kernel, stable
nfs4_decode_mp_ds_addr() decodes the r_netid and r_addr opaques of a
netaddr4 from a GETDEVICEINFO multipath-DS body, then immediately
calls strrchr(buf, '.') to locate the port separator. Both decodes
use xdr_stream_decode_string_dup(), and the current code checks only
"nlen < 0" / "rlen < 0" before dereferencing the returned string.
When the on-wire opaque has length zero, xdr_stream_decode_opaque_inline()
returns 0 and xdr_stream_decode_string_dup() falls through to its
"*str = NULL; return ret" tail, leaving buf NULL with a return value
of 0. The "< 0" check does not catch this, and the next line is
strrchr(NULL, '.'), a kernel NULL pointer dereference reachable from
any pNFS-flexfile client mounted against a malicious or compromised
metadata server.
Reject the zero-length cases explicitly so the decoder fails with
-EBADMSG (treated as a malformed GETDEVICEINFO body) instead of
panicking the client.
Cc: stable@vger.kernel.org
Fixes: 6b7f3cf96364 ("nfs41: pull decode_ds_addr from file layout to generic pnfs")
Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
Reproduced via a malicious NFSv4.1/pNFS server returning a flexfile
GETDEVICEINFO body with multipath_count >= 3 and one valid
(netid, uaddr) pair. Linux 7.0-rc7 + KASAN, QEMU/KVM. Stock kernel:
Oops: general protection fault [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
RIP: 0010:strrchr+0x24/0x80
Call Trace:
nfs4_decode_mp_ds_addr+0xca/0x570
nfs4_ff_alloc_deviceid_node+0x357/0x1370
nfs4_find_get_deviceid+0x6b6/0xa90
nfs4_ff_layout_prepare_ds+0x3cf/0xa40
ff_layout_choose_ds_for_read+0x14c/0x350
ff_layout_pg_init_read+0x2a2/0xb90
...
nfs_file_splice_read+0xcf/0x190
do_sendfile+0x8eb/0xdf0
Kernel panic - not syncing: Fatal exception
Deterministic for any multipath_count >= 3; multipath_count <= 2
does not crash because the loop ends before consuming the malformed
trailing bytes.
Patched kernel rejects the same crafted body and a baseline
multipath_count = 1 mount + read completes normally.
fs/nfs/pnfs_nfs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/nfs/pnfs_nfs.c b/fs/nfs/pnfs_nfs.c
index 12632a706da88..0ff43dbcb7cd7 100644
--- a/fs/nfs/pnfs_nfs.c
+++ b/fs/nfs/pnfs_nfs.c
@@ -1075,14 +1075,14 @@ nfs4_decode_mp_ds_addr(struct net *net, struct xdr_stream *xdr, gfp_t gfp_flags)
/* r_netid */
nlen = xdr_stream_decode_string_dup(xdr, &netid, XDR_MAX_NETOBJ,
gfp_flags);
- if (unlikely(nlen < 0))
+ if (unlikely(nlen <= 0))
goto out_err;
/* r_addr: ip/ip6addr with port in dec octets - see RFC 5665 */
/* port is ".ABC.DEF", 8 chars max */
rlen = xdr_stream_decode_string_dup(xdr, &buf, INET6_ADDRSTRLEN +
IPV6_SCOPE_ID_LEN + 8, gfp_flags);
- if (unlikely(rlen < 0))
+ if (unlikely(rlen <= 0))
goto out_free_netid;
/* replace port '.' with '-' */
--
2.53.0
^ permalink raw reply [flat|nested] 3+ messages in thread* [PATCH v2 2/2] NFSv4/flexfile,filelayout: bound multipath DS count in GETDEVICEINFO
2026-05-27 16:30 [PATCH v2 0/2] NFSv4/pNFS: fix client kernel panic from malformed GETDEVICEINFO Michael Bommarito
2026-05-27 16:30 ` [PATCH v2 1/2] NFSv4/pNFS: reject zero-length r_addr in nfs4_decode_mp_ds_addr Michael Bommarito
@ 2026-05-27 16:30 ` Michael Bommarito
1 sibling, 0 replies; 3+ messages in thread
From: Michael Bommarito @ 2026-05-27 16:30 UTC (permalink / raw)
To: Trond Myklebust, Anna Schumaker
Cc: Jeff Layton, Tom Haynes, Peng Tao, Kees Cook, Mike Snitzer,
Tigran Mkrtchyan, linux-nfs, linux-kernel, stable
Both the flexfile and the (legacy) file pNFS layout drivers decode a
multipath-DS count from a server-supplied GETDEVICEINFO body and then
iterate it via nfs4_decode_mp_ds_addr() without any upper bound. The
filelayout driver already caps the outer ds_num against
NFS4_PNFS_MAX_MULTI_CNT (== 256) but applies no equivalent cap to the
inner mp_count; the flexfile driver applies no cap on either.
In addition, both inner loops ignore a NULL return from
nfs4_decode_mp_ds_addr(), so once the on-wire data no longer matches
a valid netaddr4 encoding the loop is free to consume the trailing
bytes of the device_addr opaque as garbage netid + uaddr pairs. A
malicious or compromised pNFS metadata server can therefore drive
the inner loop indefinitely (up to 2^32 - 1 iterations) against a
fixed-size 56-byte body, with each iteration triggering an
allocation / kmemdup_nul cycle inside the decoder.
Promote NFS4_PNFS_MAX_MULTI_CNT from the filelayout private header to
include/linux/nfs4.h so both drivers (and any future pNFS layout
driver that decodes a multipath address list) bound the wire-level
field consistently. Apply the cap to the inner mp_count in both
drivers, matching the existing ds_num check, and bail on the first
NULL return so a server that lies about mp_count cannot quietly
extend the loop into the trailing layout-body bytes. This is
defense-in-depth on top of the companion patch which closes the
NULL-deref in nfs4_decode_mp_ds_addr(); either patch alone closes
the kernel-panic shape, both together close the latent
unbounded-decode class.
Cc: stable@vger.kernel.org
Fixes: 35124a0994fc ("Cleanup XDR parsing for LAYOUTGET, GETDEVICEINFO")
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>
---
Changes in v2:
- Carry the stripe_index provenance comment from filelayout.h to the
new NFS4_PNFS_MAX_MULTI_CNT location in include/linux/nfs4.h, as
Anna requested.
With this patch alone the crafted GETDEVICEINFO at multipath_count >= 3
is rejected at the bound check; malformed netaddr in the inner loop
bails on the first NULL return. Either this patch or the companion
1/2 closes the panic; both together close the unbounded-decode class.
Baseline multipath_count = 1 mount + read completes normally.
fs/nfs/filelayout/filelayout.h | 2 +-
fs/nfs/filelayout/filelayoutdev.c | 7 +++++--
fs/nfs/flexfilelayout/flexfilelayoutdev.c | 10 ++++++++--
include/linux/nfs4.h | 5 +++++
4 files changed, 19 insertions(+), 5 deletions(-)
diff --git a/fs/nfs/filelayout/filelayout.h b/fs/nfs/filelayout/filelayout.h
index c7bb5da93307d..03298f2e7cd69 100644
--- a/fs/nfs/filelayout/filelayout.h
+++ b/fs/nfs/filelayout/filelayout.h
@@ -39,7 +39,7 @@
* RFC 5661 multipath_list4 structures.
*/
#define NFS4_PNFS_MAX_STRIPE_CNT 4096
-#define NFS4_PNFS_MAX_MULTI_CNT 256 /* 256 fit into a u8 stripe_index */
+/* NFS4_PNFS_MAX_MULTI_CNT now in <linux/nfs4.h>; shared with flexfile. */
enum stripetype4 {
STRIPE_SPARSE = 1,
diff --git a/fs/nfs/filelayout/filelayoutdev.c b/fs/nfs/filelayout/filelayoutdev.c
index 7226989ee4d53..c58c786dcf011 100644
--- a/fs/nfs/filelayout/filelayoutdev.c
+++ b/fs/nfs/filelayout/filelayoutdev.c
@@ -159,10 +159,13 @@ nfs4_fl_alloc_deviceid_node(struct nfs_server *server, struct pnfs_device *pdev,
goto out_err_free_deviceid;
mp_count = be32_to_cpup(p); /* multipath count */
+ if (mp_count > NFS4_PNFS_MAX_MULTI_CNT)
+ goto out_err_free_deviceid;
for (j = 0; j < mp_count; j++) {
da = nfs4_decode_mp_ds_addr(net, &stream, gfp_flags);
- if (da)
- list_add_tail(&da->da_node, &dsaddrs);
+ if (!da)
+ break;
+ list_add_tail(&da->da_node, &dsaddrs);
}
if (list_empty(&dsaddrs)) {
dprintk("%s: no suitable DS addresses found\n",
diff --git a/fs/nfs/flexfilelayout/flexfilelayoutdev.c b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
index c40395ae08142..faed05cbe9f1c 100644
--- a/fs/nfs/flexfilelayout/flexfilelayoutdev.c
+++ b/fs/nfs/flexfilelayout/flexfilelayoutdev.c
@@ -78,12 +78,18 @@ nfs4_ff_alloc_deviceid_node(struct nfs_server *server, struct pnfs_device *pdev,
goto out_err_drain_dsaddrs;
mp_count = be32_to_cpup(p);
dprintk("%s: multipath ds count %d\n", __func__, mp_count);
+ if (mp_count > NFS4_PNFS_MAX_MULTI_CNT) {
+ dprintk("%s: multipath count %u greater than supported maximum %d\n",
+ __func__, mp_count, NFS4_PNFS_MAX_MULTI_CNT);
+ goto out_err_drain_dsaddrs;
+ }
for (i = 0; i < mp_count; i++) {
/* multipath ds */
da = nfs4_decode_mp_ds_addr(net, &stream, gfp_flags);
- if (da)
- list_add_tail(&da->da_node, &dsaddrs);
+ if (!da)
+ break;
+ list_add_tail(&da->da_node, &dsaddrs);
}
if (list_empty(&dsaddrs)) {
dprintk("%s: no suitable DS addresses found\n",
diff --git a/include/linux/nfs4.h b/include/linux/nfs4.h
index d87be1f25273a..79f4168cb6ab7 100644
--- a/include/linux/nfs4.h
+++ b/include/linux/nfs4.h
@@ -767,6 +767,11 @@ enum pnfs_block_extent_state {
PNFS_BLOCK_NONE_DATA = 3,
};
+/* Maximum NFSv4.1 pNFS multipath data-server address count;
+ * 256 fits in the u8 stripe_index used by the filelayout driver.
+ */
+#define NFS4_PNFS_MAX_MULTI_CNT 256
+
/* on the wire size of a block layout extent */
#define PNFS_BLOCK_EXTENT_SIZE \
(7 * sizeof(__be32) + NFS4_DEVICEID4_SIZE)
--
2.53.0
^ permalink raw reply [flat|nested] 3+ messages in thread