linux-kernel - Re: [PATCH] net: check the return value of the copy_from

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Message-ID: <ZuFv88V0qhcwfOgP@iZbp1asjb3cy8ks0srf007Z>
Date: Wed, 11 Sep 2024 18:24:51 +0800
From: Qianqiang Liu <qianqiang.liu@....com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Tze-nan.Wu@...iatek.com, xiyou.wangcong@...il.com, davem@...emloft.net,
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: check the return value of the copy_from_sockptr

On Wed, Sep 11, 2024 at 11:12:24AM +0200, Eric Dumazet wrote:
> On Wed, Sep 11, 2024 at 10:23 AM Qianqiang Liu <qianqiang.liu@....com> wrote:
> >
> > > I do not think it matters, because the copy is performed later, with
> > > all the needed checks.
> >
> > No, there is no checks at all.
> >
> 
> Please elaborate ?
> Why should maintainers have to spend time to provide evidence to
> support your claims ?
> Have you thought about the (compat) case ?
> 
> There are plenty of checks. They were there before Stanislav commit.
> 
> Each getsockopt() handler must perform the same actions.
> 
> For instance, look at do_ipv6_getsockopt()
> 
> If you find one getsockopt() method failing to perform the checks,
> please report to us.

Sorry, let me explain a little bit.

The issue was introduced in this commit: 33f339a1ba54e ("bpf, net: Fix a
potential race in do_sock_getsockopt()")

diff --git a/net/socket.c b/net/socket.c
index fcbdd5bc47ac..0a2bd22ec105 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2362,7 +2362,7 @@ INDIRECT_CALLABLE_DECLARE(bool tcp_bpf_bypass_getsockopt(int level,
 int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 		       int optname, sockptr_t optval, sockptr_t optlen)
 {
-	int max_optlen __maybe_unused;
+	int max_optlen __maybe_unused = 0;
 	const struct proto_ops *ops;
 	int err;
 
@@ -2371,7 +2371,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 		return err;
 
 	if (!compat)
-		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
+		copy_from_sockptr(&max_optlen, optlen, sizeof(int));
 
 	ops = READ_ONCE(sock->ops);
 	if (level == SOL_SOCKET) {

The return value of "copy_from_sockptr()" in "do_sock_getsockopt()" was
not checked. So, I added the following patch:

diff --git a/net/socket.c b/net/socket.c
index 0a2bd22ec105..6b9a414d01d5 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2370,8 +2370,11 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 	if (err)
 		return err;
 
-	if (!compat)
-		copy_from_sockptr(&max_optlen, optlen, sizeof(int));
+	if (!compat) {
+		err = copy_from_sockptr(&max_optlen, optlen, sizeof(int));
+		if (err)
+			return -EFAULT;
+	}
 
 	ops = READ_ONCE(sock->ops);
 	if (level == SOL_SOCKET) {

Maybe I missed something?

If you think it's not an issue, then I'm OK with it.

-- 
Best,
Qianqiang Liu