Re: [PATCH] net: rds: fix memory leak in rds_recvmsg

On Tue, 8 Jun 2021 07:11:27 +0000
Haakon Bugge [off-list ref] wrote:

quoted

On 7 Jun 2021, at 21:41, Pavel Skripkin [off-list ref]
wrote:

Syzbot reported memory leak in rds. The problem
was in unputted refcount in case of error.

int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t
size, int msg_flags)
{
...

	if (!rds_next_incoming(rs, &inc)) {
		...
	}

After this "if" inc refcount incremented and

	if (rds_cmsg_recv(inc, msg, rs)) {
		ret = -EFAULT;
		goto out;
	}
...
out:
	return ret;
}

in case of rds_cmsg_recv() fail the refcount won't be
decremented. And it's easy to see from ftrace log, that
rds_inc_addref() don't have rds_inc_put() pair in
rds_recvmsg() after rds_cmsg_recv()

1)               |  rds_recvmsg() {
1)   3.721 us    |    rds_inc_addref();
1)   3.853 us    |    rds_message_inc_copy_to_user();
1) + 10.395 us   |    rds_cmsg_recv();
1) + 34.260 us   |  }

Fixes: bdbe6fbc6a2f ("RDS: recv.c")
Reported-and-tested-by:
syzbot+5134cdf021c4ed5aaa5f@syzkaller.appspotmail.com
Signed-off-by: Pavel Skripkin <redacted>

Thank for your commit and analyses. One small nit below.

quoted

---
net/rds/recv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/rds/recv.c b/net/rds/recv.c
index 4db109fb6ec2..3fa16c339bfe 100644
--- a/net/rds/recv.c
+++ b/net/rds/recv.c

@@ -714,7 +714,7 @@ int rds_recvmsg(struct socket *sock, struct

msghdr *msg, size_t size,

		if (rds_cmsg_recv(inc, msg, rs)) {
			ret = -EFAULT;
-			goto out;
+			goto out_put;

Would a simple "break;" do it here and no need for the next hunk?


Thxs, Håkon

Sure! I'll send v2 soon. Thank you for feedback :)


With regards,
Pavel Skripkin