Commit 2aab4b96 authored Mar 07, 2023 by Eric Dumazet Committed by Jakub Kicinski Mar 08, 2023

af_unix: fix struct pid leaks in OOB support



syzbot reported struct pid leak [1].

Issue is that queue_oob() calls maybe_add_creds() which potentially
holds a reference on a pid.

But skb->destructor is not set (either directly or by calling
unix_scm_to_skb())

This means that subsequent kfree_skb() or consume_skb() would leak
this reference.

In this fix, I chose to fully support scm even for the OOB message.

[1]
BUG: memory leak
unreferenced object 0xffff8881053e7f80 (size 128):
comm "syz-executor242", pid 5066, jiffies 4294946079 (age 13.220s)
hex dump (first 32 bytes):
01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<ffffffff812ae26a>] alloc_pid+0x6a/0x560 kernel/pid.c:180
[<ffffffff812718df>] copy_process+0x169f/0x26c0 kernel/fork.c:2285
[<ffffffff81272b37>] kernel_clone+0xf7/0x610 kernel/fork.c:2684
[<ffffffff812730cc>] __do_sys_clone+0x7c/0xb0 kernel/fork.c:2825
[<ffffffff849ad699>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<ffffffff849ad699>] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
[<ffffffff84a0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 314001f0 ("af_unix: Add OOB support")
Reported-by:  <syzbot+7699d9e5635c10253a27@syzkaller.appspotmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Rao Shoaib <rao.shoaib@oracle.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230307164530.771896-1-edumazet@google.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>

parent 8f148208

net/unix/af_unix.c

+8 −2

Original line number	Diff line number	Diff line
		@@ -2105,7 +2105,8 @@ static int unix_dgram_sendmsg(struct socket sock, struct msghdr msg,
		#define UNIX_SKB_FRAGS_SZ (PAGE_SIZE << get_order(32768))

		#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
		static int queue_oob(struct socket sock, struct msghdr msg, struct sock *other)
		static int queue_oob(struct socket sock, struct msghdr msg, struct sock *other,
		struct scm_cookie *scm, bool fds_sent)
		{
		struct unix_sock *ousk = unix_sk(other);
		struct sk_buff *skb;
		@@ -2116,6 +2117,11 @@ static int queue_oob(struct socket sock, struct msghdr msg, struct sock *other
		if (!skb)
		return err;

		err = unix_scm_to_skb(scm, skb, !fds_sent);
		if (err < 0) {
		kfree_skb(skb);
		return err;
		}
		skb_put(skb, 1);
		err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);

		@@ -2243,7 +2249,7 @@ static int unix_stream_sendmsg(struct socket sock, struct msghdr msg,

		#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
		if (msg->msg_flags & MSG_OOB) {
		err = queue_oob(sock, msg, other);
		err = queue_oob(sock, msg, other, &scm, fds_sent);
		if (err)
		goto out_err;
		sent++;