decode_cb_sequence_args() allocates csa_rclists with kmalloc_objs(), so
each referring_call_list starts uninitialized. decode_rc_list() assigns
rcl_refcalls only when rcl_nrefcalls is nonzero. A valid list with zero
referring calls therefore leaves the pointer uninitialized, and
nfs4_callback_sequence() later passes stale slab contents to kfree().

Allocate csa_rclists with kzalloc_objs() so every rcl_refcalls member is
NULL from the beginning, including valid empty referring call lists.

Fixes: 4aece6a19cf7 ("nfs41: cb_sequence xdr implementation")
Assisted-by: Codex:gpt-5
Signed-off-by: Jérémy Jean <Jeremy.Jean@oss.cyber.gouv.fr>
---
Changes in v2:
- On Anna's suggestion, use kzalloc_objs() for csa_rclists instead of 
  initializing each list in decode_rc_list()

v1: https://lore.kernel.org/linux-nfs/ae822c8b-9d47-4a96-a61b-aef730c4c785@app.fastmail.com/T/

 fs/nfs/callback_xdr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/nfs/callback_xdr.c b/fs/nfs/callback_xdr.c
index eec6040556c9..88e1af0fda01 100644
--- a/fs/nfs/callback_xdr.c
+++ b/fs/nfs/callback_xdr.c
@@ -417,7 +417,7 @@ static __be32 decode_cb_sequence_args(struct svc_rqst *rqstp,
 	args->csa_nrclists = ntohl(*p++);
 	args->csa_rclists = NULL;
 	if (args->csa_nrclists) {
-		args->csa_rclists = kmalloc_objs(*args->csa_rclists,
+		args->csa_rclists = kzalloc_objs(*args->csa_rclists,
 						 args->csa_nrclists);
 		if (unlikely(args->csa_rclists == NULL))
 			return htonl(NFS4ERR_RESOURCE);
-- 
2.47.3