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

From: Pavel Skripkin <[email-masked]>
Date: Tue, 8 Jun 2021 11:00:06 +0300

On Tue, 8 Jun 2021 07:11:27 +0000
Haakon Bugge <[email-masked]> wrote:

> 
> 
> > On 7 Jun 2021, at 21:41, Pavel Skripkin <[email-masked]>
> > 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:
> > [email-masked]
> > Signed-off-by: Pavel Skripkin <[email-masked]>
> 
> Thank for your commit and analyses. One small nit below.
> 
> > ---
> > 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