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From:   Deepa Dinamani <deepa.kernel@gmail.com>
To:     linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk
Cc:     akpm@linux-foundation.org, arnd@arndb.de, dbueso@suse.de,
        axboe@kernel.dk, dave@stgolabs.net, e@80x24.org, jbaron@akamai.com,
        linux-fsdevel@vger.kernel.org, linux-aio@kvack.org,
        omar.kilani@gmail.com, tglx@linutronix.de
Subject: [PATCH 1/1] signal: Adjust error codes according to restore_user_sigmask()
Date:   Mon,  6 May 2019 21:39:54 -0700
Message-Id: <20190507043954.9020-1-deepa.kernel@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

For all the syscalls that receive a sigmask from the userland,
the user sigmask is to be in effect through the syscall execution.
At the end of syscall, sigmask of the current process is restored
to what it was before the switch over to user sigmask.
But, for this to be true in practice, the sigmask should be restored
only at the the point we change the saved_sigmask. Anything before
that loses signals. And, anything after is just pointless as the
signal is already lost by restoring the sigmask.

The inherent issue was detected because of a regression caused by
854a6ed56839a.
The patch moved the signal_pending() check closer to restoring of the
user sigmask. But, it failed to update the error code accordingly.

Detailed issue discussion permalink:
https://lore.kernel.org/linux-fsdevel/20190427093319.sgicqik2oqkez3wk@dcvr/

Note that the patch returns interrupted errors (EINTR, ERESTARTNOHAND,
etc) only when there is no other error. If there is a signal and an error
like EINVAL, the syscalls return -EINVAL rather than the interrupted
error codes.

The sys_io_uring_enter() seems to be returning success when there is
a signal and the queue is not empty. This seems to be a bug. I will
follow up with a separate patch for that.

Reported-by: Eric Wong <e@80x24.org>
Fixes: 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add restore_user_sigmask()")
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
---

 fs/aio.c               | 24 ++++++++++++------------
 fs/eventpoll.c         | 14 ++++++++++----
 fs/io_uring.c          |  9 ++++++---
 fs/select.c            | 37 +++++++++++++++++++++----------------
 include/linux/signal.h |  2 +-
 kernel/signal.c        | 13 ++++++++++---
 6 files changed, 60 insertions(+), 39 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 3490d1fa0e16..ebd2b1980161 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -2095,7 +2095,7 @@ SYSCALL_DEFINE6(io_pgetevents,
 	struct __aio_sigset	ksig = { NULL, };
 	sigset_t		ksigmask, sigsaved;
 	struct timespec64	ts;
-	int ret;
+	int ret, signal_detected;
 
 	if (timeout && unlikely(get_timespec64(&ts, timeout)))
 		return -EFAULT;
@@ -2108,8 +2108,8 @@ SYSCALL_DEFINE6(io_pgetevents,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
-	restore_user_sigmask(ksig.sigmask, &sigsaved);
-	if (signal_pending(current) && !ret)
+	signal_detected = restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_detected && !ret)
 		ret = -ERESTARTNOHAND;
 
 	return ret;
@@ -2128,7 +2128,7 @@ SYSCALL_DEFINE6(io_pgetevents_time32,
 	struct __aio_sigset	ksig = { NULL, };
 	sigset_t		ksigmask, sigsaved;
 	struct timespec64	ts;
-	int ret;
+	int ret, signal_detected;
 
 	if (timeout && unlikely(get_old_timespec32(&ts, timeout)))
 		return -EFAULT;
@@ -2142,8 +2142,8 @@ SYSCALL_DEFINE6(io_pgetevents_time32,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &ts : NULL);
-	restore_user_sigmask(ksig.sigmask, &sigsaved);
-	if (signal_pending(current) && !ret)
+	signal_detected = restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_detected && !ret)
 		ret = -ERESTARTNOHAND;
 
 	return ret;
@@ -2193,7 +2193,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
 	struct __compat_aio_sigset ksig = { NULL, };
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 t;
-	int ret;
+	int ret, signal_detected;
 
 	if (timeout && get_old_timespec32(&t, timeout))
 		return -EFAULT;
@@ -2206,8 +2206,8 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
-	restore_user_sigmask(ksig.sigmask, &sigsaved);
-	if (signal_pending(current) && !ret)
+	signal_detected = restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_detected && !ret)
 		ret = -ERESTARTNOHAND;
 
 	return ret;
@@ -2226,7 +2226,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
 	struct __compat_aio_sigset ksig = { NULL, };
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 t;
-	int ret;
+	int ret, signal_detected;
 
 	if (timeout && get_timespec64(&t, timeout))
 		return -EFAULT;
@@ -2239,8 +2239,8 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_time64,
 		return ret;
 
 	ret = do_io_getevents(ctx_id, min_nr, nr, events, timeout ? &t : NULL);
-	restore_user_sigmask(ksig.sigmask, &sigsaved);
-	if (signal_pending(current) && !ret)
+	signal_detected = restore_user_sigmask(ksig.sigmask, &sigsaved);
+	if (signal_detected && !ret)
 		ret = -ERESTARTNOHAND;
 
 	return ret;
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4a0e98d87fcc..fe5a0724b417 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2317,7 +2317,7 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
 		int, maxevents, int, timeout, const sigset_t __user *, sigmask,
 		size_t, sigsetsize)
 {
-	int error;
+	int error, signal_detected;
 	sigset_t ksigmask, sigsaved;
 
 	/*
@@ -2330,7 +2330,10 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd, struct epoll_event __user *, events,
 
 	error = do_epoll_wait(epfd, events, maxevents, timeout);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
+
+	if (signal_detected && !error)
+		error = -EINTR;
 
 	return error;
 }
@@ -2342,7 +2345,7 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
 			const compat_sigset_t __user *, sigmask,
 			compat_size_t, sigsetsize)
 {
-	long err;
+	long err, signal_detected;
 	sigset_t ksigmask, sigsaved;
 
 	/*
@@ -2355,7 +2358,10 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int, epfd,
 
 	err = do_epoll_wait(epfd, events, maxevents, timeout);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
+
+	if (signal_detected && !err)
+		err = -EINTR;
 
 	return err;
 }
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 452e35357865..8fd4710f371d 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2195,7 +2195,7 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 	struct io_cq_ring *ring = ctx->cq_ring;
 	sigset_t ksigmask, sigsaved;
 	DEFINE_WAIT(wait);
-	int ret;
+	int ret, signal_detected;
 
 	/* See comment at the top of this file */
 	smp_rmb();
@@ -2234,8 +2234,11 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 
 	finish_wait(&ctx->wait, &wait);
 
-	if (sig)
-		restore_user_sigmask(sig, &sigsaved);
+	if (sig) {
+		signal_detected = restore_user_sigmask(sig, &sigsaved);
+		if (signal_detected && !ret)
+			ret  = -EINTR;
+	}
 
 	return READ_ONCE(ring->r.head) == READ_ONCE(ring->r.tail) ? ret : 0;
 }
diff --git a/fs/select.c b/fs/select.c
index 6cbc9ff56ba0..da9cfea35159 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -732,7 +732,7 @@ static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		switch (type) {
@@ -760,7 +760,9 @@ static long do_pselect(int n, fd_set __user *inp, fd_set __user *outp,
 	ret = core_sys_select(n, inp, outp, exp, to);
 	ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
+	if (signal_detected && !ret)
+		ret = -EINTR;
 
 	return ret;
 }
@@ -1089,7 +1091,7 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		if (get_timespec64(&ts, tsp))
@@ -1106,10 +1108,10 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __user *, ufds, unsigned int, nfds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
 
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR)
+	if (ret == -EINTR || (signal_detected && !ret))
 		ret = -ERESTARTNOHAND;
 
 	ret = poll_select_copy_remaining(&end_time, tsp, PT_TIMESPEC, ret);
@@ -1125,7 +1127,7 @@ SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds, unsigned int, nfds,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		if (get_old_timespec32(&ts, tsp))
@@ -1142,10 +1144,10 @@ SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds, unsigned int, nfds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
 
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR)
+	if (ret == -EINTR || (signal_detected && !ret))
 		ret = -ERESTARTNOHAND;
 
 	ret = poll_select_copy_remaining(&end_time, tsp, PT_OLD_TIMESPEC, ret);
@@ -1324,7 +1326,7 @@ static long do_compat_pselect(int n, compat_ulong_t __user *inp,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		switch (type) {
@@ -1352,7 +1354,10 @@ static long do_compat_pselect(int n, compat_ulong_t __user *inp,
 	ret = compat_core_sys_select(n, inp, outp, exp, to);
 	ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
+
+	if (signal_detected && !ret)
+		ret = -EINTR;
 
 	return ret;
 }
@@ -1408,7 +1413,7 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		if (get_old_timespec32(&ts, tsp))
@@ -1425,10 +1430,10 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time32, struct pollfd __user *, ufds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
 
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR)
+	if (ret == -EINTR || (signal_detected && !ret))
 		ret = -ERESTARTNOHAND;
 
 	ret = poll_select_copy_remaining(&end_time, tsp, PT_OLD_TIMESPEC, ret);
@@ -1444,7 +1449,7 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time64, struct pollfd __user *, ufds,
 {
 	sigset_t ksigmask, sigsaved;
 	struct timespec64 ts, end_time, *to = NULL;
-	int ret;
+	int ret, signal_detected;
 
 	if (tsp) {
 		if (get_timespec64(&ts, tsp))
@@ -1461,10 +1466,10 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time64, struct pollfd __user *, ufds,
 
 	ret = do_sys_poll(ufds, nfds, to);
 
-	restore_user_sigmask(sigmask, &sigsaved);
+	signal_detected = restore_user_sigmask(sigmask, &sigsaved);
 
 	/* We can restart this syscall, usually */
-	if (ret == -EINTR)
+	if (ret == -EINTR || (signal_detected && !ret))
 		ret = -ERESTARTNOHAND;
 
 	ret = poll_select_copy_remaining(&end_time, tsp, PT_TIMESPEC, ret);
diff --git a/include/linux/signal.h b/include/linux/signal.h
index 9702016734b1..1d36e8629edf 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -275,7 +275,7 @@ extern int __group_send_sig_info(int, struct kernel_siginfo *, struct task_struc
 extern int sigprocmask(int, sigset_t *, sigset_t *);
 extern int set_user_sigmask(const sigset_t __user *usigmask, sigset_t *set,
 	sigset_t *oldset, size_t sigsetsize);
-extern void restore_user_sigmask(const void __user *usigmask,
+extern int restore_user_sigmask(const void __user *usigmask,
 				 sigset_t *sigsaved);
 extern void set_current_blocked(sigset_t *);
 extern void __set_current_blocked(const sigset_t *);
diff --git a/kernel/signal.c b/kernel/signal.c
index e46d527ff467..ea0321b70315 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2906,15 +2906,21 @@ EXPORT_SYMBOL(set_compat_user_sigmask);
  * usigmask: sigmask passed in from userland.
  * sigsaved: saved sigmask when the syscall started and changed the sigmask to
  *           usigmask.
+ * returns 1 in case a pending signal is detected.
+ *
+ * Users of the api need to adjust their return values based on whether the
+ * signal was detected here. If a signal is detected, it is delivered to the
+ * userspace. So without an error like -EINTR, userspace might fail to
+ * adjust the flow of execution.
  *
  * This is useful for syscalls such as ppoll, pselect, io_pgetevents and
  * epoll_pwait where a new sigmask is passed in from userland for the syscalls.
  */
-void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
+int restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
 {
 
 	if (!usigmask)
-		return;
+		return 0;
 	/*
 	 * When signals are pending, do not restore them here.
 	 * Restoring sigmask here can lead to delivering signals that the above
@@ -2923,7 +2929,7 @@ void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
 	if (signal_pending(current)) {
 		current->saved_sigmask = *sigsaved;
 		set_restore_sigmask();
-		return;
+		return 1;
 	}
 
 	/*
@@ -2931,6 +2937,7 @@ void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved)
 	 * saved_sigmask when signals are not pending.
 	 */
 	set_current_blocked(sigsaved);
+	return 0;
 }
 EXPORT_SYMBOL(restore_user_sigmask);
 
-- 
2.17.1