net/rds: remove user triggered WARN_ON in rds_sendmsg

per comment from Leon in rdma mailing list
https://lkml.org/lkml/2018/10/31/312 :

Please don't forget to remove user triggered WARN_ON.
https://lwn.net/Articles/769365/
"Greg Kroah-Hartman raised the problem of core kernel API code that will
use WARN_ON_ONCE() to complain about bad usage; that will not generate
the desired result if WARN_ON_ONCE() is configured to crash the machine.
He was told that the code should just call pr_warn() instead, and that
the called function should return an error in such situations. It was
generally agreed that any WARN_ON() or WARN_ON_ONCE() calls that can be
triggered from user space need to be fixed."

in addition harden rds_sendmsg to detect and overcome issues with
invalid sg count and fail the sendmsg.

Suggested-by: Leon Romanovsky <leon@kernel.org>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: shamir rabinovitch <shamir.rabinovitch@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 4 deletions

diff --git a/net/rds/send.c b/net/rds/send.c
index ec2267cbf85f..b39b30706210 100644
--- a/net/rds/send.c
+++ b/net/rds/send.c
@@ -886,6 +886,9 @@ static int rds_rm_size(struct msghdr *msg, int num_sgs,
 	bool zcopy_cookie = false;
 	struct rds_iov_vector *iov, *tmp_iov;
 
+	if (num_sgs < 0)
+		return -EINVAL;
+
 	for_each_cmsghdr(cmsg, msg) {
 		if (!CMSG_OK(msg, cmsg))
 			return -EINVAL;
@@ -1259,11 +1262,9 @@ int rds_sendmsg(struct socket *sock, struct msghdr *msg, size_t payload_len)
 
 	/* Attach data to the rm */
 	if (payload_len) {
-		rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
-		if (!rm->data.op_sg) {
-			ret = -ENOMEM;
+		rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs, &ret);
+		if (!rm->data.op_sg)
 			goto out;
-		}
 		ret = rds_message_copy_from_user(rm, &msg->msg_iter, zcopy);
 		if (ret)
 			goto out;