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

[Haakon Bugge]

> On 7 Jun 2021, at 21:41, Pavel Skripkin <paskripkin@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Pavel Skripkin <paskripkin@xxxxxxxxx>

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

> 		}
> 		rds_recvmsg_zcookie(rs, msg);
> 
> @@ -740,6 +740,7 @@ int rds_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
> 		break;
> 	}
> 
> +out_put:
> 	if (inc)
> 		rds_inc_put(inc);
> 
> -- 
> 2.31.1
>