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, 18 insertions, 6 deletions

diff --git a/net/rds/message.c b/net/rds/message.c
index 4b00b1152a5f..f139420ba1f6 100644
--- a/net/rds/message.c
+++ b/net/rds/message.c
@@ -308,16 +308,27 @@ out:
 /*
  * RDS ops use this to grab SG entries from the rm's sg pool.
  */
-struct scatterlist *rds_message_alloc_sgs(struct rds_message *rm, int nents)
+struct scatterlist *rds_message_alloc_sgs(struct rds_message *rm, int nents,
+					  int *ret)
 {
 	struct scatterlist *sg_first = (struct scatterlist *) &rm[1];
 	struct scatterlist *sg_ret;
 
-	WARN_ON(rm->m_used_sgs + nents > rm->m_total_sgs);
-	WARN_ON(!nents);
+	if (WARN_ON(!ret))
+		return NULL;
 
-	if (rm->m_used_sgs + nents > rm->m_total_sgs)
+	if (nents <= 0) {
+		pr_warn("rds: alloc sgs failed! nents <= 0\n");
+		*ret = -EINVAL;
 		return NULL;
+	}
+
+	if (rm->m_used_sgs + nents > rm->m_total_sgs) {
+		pr_warn("rds: alloc sgs failed! total %d used %d nents %d\n",
+			rm->m_total_sgs, rm->m_used_sgs, nents);
+		*ret = -ENOMEM;
+		return NULL;
+	}
 
 	sg_ret = &sg_first[rm->m_used_sgs];
 	sg_init_table(sg_ret, nents);
@@ -332,6 +343,7 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
 	unsigned int i;
 	int num_sgs = ceil(total_len, PAGE_SIZE);
 	int extra_bytes = num_sgs * sizeof(struct scatterlist);
+	int ret;
 
 	rm = rds_message_alloc(extra_bytes, GFP_NOWAIT);
 	if (!rm)
@@ -340,10 +352,10 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
 	set_bit(RDS_MSG_PAGEVEC, &rm->m_flags);
 	rm->m_inc.i_hdr.h_len = cpu_to_be32(total_len);
 	rm->data.op_nents = ceil(total_len, PAGE_SIZE);
-	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
+	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs, &ret);
 	if (!rm->data.op_sg) {
 		rds_message_put(rm);
-		return ERR_PTR(-ENOMEM);
+		return ERR_PTR(ret);
 	}
 
 	for (i = 0; i < rm->data.op_nents; ++i) {