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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Peilin Ye , George Zhang , Dmitry Torokhov , Andy King , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Peilin Ye Subject: [PATCH net v3 1/2] vsock: Fix memory leak in vsock_connect() Date: Mon, 8 Aug 2022 11:04:47 -0700 Message-Id: X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Peilin Ye An O_NONBLOCK vsock_connect() request may try to reschedule @connect_work. Imagine the following sequence of vsock_connect() requests: 1. The 1st, non-blocking request schedules @connect_work, which will expire after 200 jiffies. Socket state is now SS_CONNECTING; 2. Later, the 2nd, blocking request gets interrupted by a signal after a few jiffies while waiting for the connection to be established. Socket state is back to SS_UNCONNECTED, but @connect_work is still pending, and will expire after 100 jiffies. 3. Now, the 3rd, non-blocking request tries to schedule @connect_work again. Since @connect_work is already scheduled, schedule_delayed_work() silently returns. sock_hold() is called twice, but sock_put() will only be called once in vsock_connect_timeout(), causing a memory leak reported by syzbot: BUG: memory leak unreferenced object 0xffff88810ea56a40 (size 1232): comm "syz-executor756", pid 3604, jiffies 4294947681 (age 12.350s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 28 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 (..@............ backtrace: [] sk_prot_alloc+0x3e/0x1b0 net/core/sock.c:1930 [] sk_alloc+0x32/0x2e0 net/core/sock.c:1989 [] __vsock_create.constprop.0+0x38/0x320 net/vmw_vsock/af_vsock.c:734 [] vsock_create+0xc1/0x2d0 net/vmw_vsock/af_vsock.c:2203 [] __sock_create+0x1ab/0x2b0 net/socket.c:1468 [] sock_create net/socket.c:1519 [inline] [] __sys_socket+0x6f/0x140 net/socket.c:1561 [] __do_sys_socket net/socket.c:1570 [inline] [] __se_sys_socket net/socket.c:1568 [inline] [] __x64_sys_socket+0x1a/0x20 net/socket.c:1568 [] do_syscall_x64 arch/x86/entry/common.c:50 [inline] [] do_syscall_64+0x35/0x80 arch/x86/entry/common.c:80 [] entry_SYSCALL_64_after_hwframe+0x44/0xae <...> Use mod_delayed_work() instead: if @connect_work is already scheduled, reschedule it, and undo sock_hold() to keep the reference count balanced. Reported-and-tested-by: syzbot+b03f55bf128f9a38f064@syzkaller.appspotmail.com Fixes: d021c344051a ("VSOCK: Introduce VM Sockets") Co-developed-by: Stefano Garzarella Signed-off-by: Stefano Garzarella Reviewed-by: Stefano Garzarella Signed-off-by: Peilin Ye --- change since v2: - wrapped long line (Stefano) change since v1: - merged with Stefano's patch [1] [1] https://gitlab.com/sgarzarella/linux/-/commit/2d0f0b9cbbb30d58fdcbca7c1a857fd8f3110d61 net/vmw_vsock/af_vsock.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c index f04abf662ec6..4d68681f5abe 100644 --- a/net/vmw_vsock/af_vsock.c +++ b/net/vmw_vsock/af_vsock.c @@ -1391,7 +1391,14 @@ static int vsock_connect(struct socket *sock, struct sockaddr *addr, * timeout fires. */ sock_hold(sk); - schedule_delayed_work(&vsk->connect_work, timeout); + + /* If the timeout function is already scheduled, + * reschedule it, then ungrab the socket refcount to + * keep it balanced. + */ + if (mod_delayed_work(system_wq, &vsk->connect_work, + timeout)) + sock_put(sk); /* Skip ahead to preserve error code set above. */ goto out_wait; -- 2.20.1