[PATCH 5.15.y] NFSv4/pnfs: bound the CB_NOTIFY_DEVICEID array count before allocating

[Sasha Levin <sashal@kernel.org>]

From: Benjamin Coddington <ben.coddington@hammerspace.com>

[ Upstream commit 32f0967ea296d447925465c98e7eec71d4e2f755 ]

decode_devicenotify_args() hands the server's notification count
straight to kmalloc_objs() as the array length, without checking it
against the message that carried it.  Bound it the way nfs4xdr.c bounds
an attribute length, against xdr_stream_remaining().

Fixes: 1be5683b03a7 ("pnfs: CB_NOTIFY_DEVICEID")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-fable-5
Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>
[ sashal: adjusted context for kmalloc_array() instead of kmalloc_objs() ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/nfs/callback_xdr.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index 6501459af0e57..29e43101b7158 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -272,6 +272,13 @@ __be32 decode_devicenotify_args(struct svc_rqst *rqstp,
 	if (n == 0)
 		goto out;
 
+	/* sanity check the count against the remaining stream */
+	if (n > xdr_stream_remaining(xdr) /
+		((4 * sizeof(uint32_t)) + NFS4_DEVICEID4_SIZE)) {
+		status = htonl(NFS4ERR_BADXDR);
+		goto out;
+	}
+
 	args->devs = kmalloc_array(n, sizeof(*args->devs), GFP_KERNEL);
 	if (!args->devs) {
 		status = htonl(NFS4ERR_DELAY);
-- 
2.53.0