[PATCH net v2] rds: tcp: fix uninit-value in __inet_bind

[Tabrez Ahmed <tabreztalks@gmail.com>]

KMSAN reported an uninit-value access in __inet_bind() when binding
an RDS TCP socket.

The uninitialized memory originates from rds_tcp_conn_alloc(),
which uses kmem_cache_alloc() to allocate the rds_tcp_connection structure.

Specifically, the field 't_client_port_group' is incremented in
rds_tcp_conn_path_connect() without being initialized first:

    if (++tc->t_client_port_group >= port_groups)

Since kmem_cache_alloc() does not zero the memory, this field contains
garbage, leading to the KMSAN report.

Fix this by using kmem_cache_zalloc() to ensure the structure is
zero-initialized upon allocation.

Reported-by: syzbot+aae646f09192f72a68dc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=aae646f09192f72a68dc
Tested-by: syzbot+aae646f09192f72a68dc@syzkaller.appspotmail.com
Fixes: a20a6992558f ("net/rds: Encode cp_index in TCP source port")

Signed-off-by: Tabrez Ahmed <tabreztalks@gmail.com>
---
v2:
 - Updated Fixes tag to point to commit a20a6992558f as requested by
   Charalampos Mitrodimas and Allison Henderson.
 - Explicitly mentioned 't_client_port_group' in the commit message.
 - Fixed line wrapping to be under 75 characters. 

 net/rds/tcp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/tcp.c b/net/rds/tcp.c
index 45484a93d75f..04f310255692 100644
--- a/net/rds/tcp.c
+++ b/net/rds/tcp.c
@@ -373,7 +373,7 @@ static int rds_tcp_conn_alloc(struct rds_connection *conn, gfp_t gfp)
 	int ret = 0;
 
 	for (i = 0; i < RDS_MPATH_WORKERS; i++) {
-		tc = kmem_cache_alloc(rds_tcp_conn_slab, gfp);
+		tc = kmem_cache_zalloc(rds_tcp_conn_slab, gfp);
 		if (!tc) {
 			ret = -ENOMEM;
 			goto fail;
-- 
2.43.0