[PATCH 5.1 02/96] signal: remove the wrong signal_pending() check in restore_user_sigmask()

8 Jul 2019

From: Oleg Nesterov oleg@redhat.com
commit 97abc889ee296faf95ca0e978340fb7b942a3e32 upstream.
This is the minimal fix for stable, I'll send cleanups later.
Commit 854a6ed56839 ("signal: Add restore_user_sigmask()") introduced
the visible change which breaks user-space: a signal temporary unblocked
by set_user_sigmask() can be delivered even if the caller returns
success or timeout.
Change restore_user_sigmask() to accept the additional "interrupted"
argument which should be used instead of signal_pending() check, and
update the callers.
Eric said:
: For clarity.  I don't think this is required by posix, or fundamentally to
: remove the races in select.  It is what linux has always done and we have
: applications who care so I agree this fix is needed.
:
: Further in any case where the semantic change that this patch rolls back
: (aka where allowing a signal to be delivered and the select like call to
: complete) would be advantage we can do as well if not better by using
: signalfd.
:
: Michael is there any chance we can get this guarantee of the linux
: implementation of pselect and friends clearly documented.  The guarantee
: that if the system call completes successfully we are guaranteed that no
: signal that is unblocked by using sigmask will be delivered?
Link: http://lkml.kernel.org/r/20190604134117.GA29963@redhat.com
Fixes: 854a6ed56839a40f6b5d02a2962f48841482eec4 ("signal: Add restore_user_sigmask()")
Signed-off-by: Oleg Nesterov oleg@redhat.com
Reported-by: Eric Wong e@80x24.org
Tested-by: Eric Wong e@80x24.org
Acked-by: "Eric W. Biederman" ebiederm@xmission.com
Acked-by: Arnd Bergmann arnd@arndb.de
Acked-by: Deepa Dinamani deepa.kernel@gmail.com
Cc: Michael Kerrisk mtk.manpages@gmail.com
Cc: Jens Axboe axboe@kernel.dk
Cc: Davidlohr Bueso dave@stgolabs.net
Cc: Jason Baron jbaron@akamai.com
Cc: Thomas Gleixner tglx@linutronix.de
Cc: Al Viro viro@ZenIV.linux.org.uk
Cc: David Laight David.Laight@ACULAB.COM
Cc: stable@vger.kernel.org	[5.0+]
Signed-off-by: Andrew Morton akpm@linux-foundation.org
Signed-off-by: Linus Torvalds torvalds@linux-foundation.org
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
---
 fs/aio.c               |   28 ++++++++++++++++++++--------
 fs/eventpoll.c         |    4 ++--
 fs/io_uring.c          |    2 +-
 fs/select.c            |   18 ++++++------------
 include/linux/signal.h |    2 +-
 kernel/signal.c        |    5 +++--
 6 files changed, 33 insertions(+), 26 deletions(-)

--- a/fs/aio.c
+++ b/fs/aio.c
@@ -2095,6 +2095,7 @@ SYSCALL_DEFINE6(io_pgetevents,
    struct __aio_sigset	ksig = { NULL, };
    sigset_t		ksigmask, sigsaved;
    struct timespec64	ts;
+	bool interrupted;
    int ret;
if (timeout && unlikely(get_timespec64(&ts, timeout)))
@@ -2108,8 +2109,10 @@ 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)
+
+	interrupted = signal_pending(current);
+	restore_user_sigmask(ksig.sigmask, &sigsaved, interrupted);
+	if (interrupted && !ret)
    	ret = -ERESTARTNOHAND;
return ret;
@@ -2128,6 +2131,7 @@ SYSCALL_DEFINE6(io_pgetevents_time32,
    struct __aio_sigset	ksig = { NULL, };
    sigset_t		ksigmask, sigsaved;
    struct timespec64	ts;
+	bool interrupted;
    int ret;
if (timeout && unlikely(get_old_timespec32(&ts, timeout)))
@@ -2142,8 +2146,10 @@ 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)
+
+	interrupted = signal_pending(current);
+	restore_user_sigmask(ksig.sigmask, &sigsaved, interrupted);
+	if (interrupted && !ret)
    	ret = -ERESTARTNOHAND;
return ret;
@@ -2193,6 +2199,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents,
    struct __compat_aio_sigset ksig = { NULL, };
    sigset_t ksigmask, sigsaved;
    struct timespec64 t;
+	bool interrupted;
    int ret;
if (timeout && get_old_timespec32(&t, timeout))
@@ -2206,8 +2213,10 @@ 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)
+
+	interrupted = signal_pending(current);
+	restore_user_sigmask(ksig.sigmask, &sigsaved, interrupted);
+	if (interrupted && !ret)
    	ret = -ERESTARTNOHAND;
return ret;
@@ -2226,6 +2235,7 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_tim
    struct __compat_aio_sigset ksig = { NULL, };
    sigset_t ksigmask, sigsaved;
    struct timespec64 t;
+	bool interrupted;
    int ret;
if (timeout && get_timespec64(&t, timeout))
@@ -2239,8 +2249,10 @@ COMPAT_SYSCALL_DEFINE6(io_pgetevents_tim
    	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)
+
+	interrupted = signal_pending(current);
+	restore_user_sigmask(ksig.sigmask, &sigsaved, interrupted);
+	if (interrupted && !ret)
    	ret = -ERESTARTNOHAND;
return ret;
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -2330,7 +2330,7 @@ SYSCALL_DEFINE6(epoll_pwait, int, epfd,
error = do_epoll_wait(epfd, events, maxevents, timeout);
-	restore_user_sigmask(sigmask, &sigsaved);
+	restore_user_sigmask(sigmask, &sigsaved, error == -EINTR);
return error;
 }
@@ -2355,7 +2355,7 @@ COMPAT_SYSCALL_DEFINE6(epoll_pwait, int,
err = do_epoll_wait(epfd, events, maxevents, timeout);
-	restore_user_sigmask(sigmask, &sigsaved);
+	restore_user_sigmask(sigmask, &sigsaved, err == -EINTR);
return err;
 }
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2096,7 +2096,7 @@ static int io_cqring_wait(struct io_ring
    finish_wait(&ctx->wait, &wait);
if (sig)
-		restore_user_sigmask(sig, &sigsaved);
+		restore_user_sigmask(sig, &sigsaved, ret == -EINTR);
return READ_ONCE(ring->r.head) == READ_ONCE(ring->r.tail) ? ret : 0;
 }
--- a/fs/select.c
+++ b/fs/select.c
@@ -758,10 +758,9 @@ static long do_pselect(int n, fd_set __u
    	return ret;
ret = core_sys_select(n, inp, outp, exp, to);
+	restore_user_sigmask(sigmask, &sigsaved, ret == -ERESTARTNOHAND);
    ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
-	restore_user_sigmask(sigmask, &sigsaved);
-
    return ret;
 }
@@ -1106,8 +1105,7 @@ SYSCALL_DEFINE5(ppoll, struct pollfd __u
ret = do_sys_poll(ufds, nfds, to);
-	restore_user_sigmask(sigmask, &sigsaved);
-
+	restore_user_sigmask(sigmask, &sigsaved, ret == -EINTR);
    /* We can restart this syscall, usually */
    if (ret == -EINTR)
    	ret = -ERESTARTNOHAND;
@@ -1142,8 +1140,7 @@ SYSCALL_DEFINE5(ppoll_time32, struct pol
ret = do_sys_poll(ufds, nfds, to);
-	restore_user_sigmask(sigmask, &sigsaved);
-
+	restore_user_sigmask(sigmask, &sigsaved, ret == -EINTR);
    /* We can restart this syscall, usually */
    if (ret == -EINTR)
    	ret = -ERESTARTNOHAND;
@@ -1350,10 +1347,9 @@ static long do_compat_pselect(int n, com
    	return ret;
ret = compat_core_sys_select(n, inp, outp, exp, to);
+	restore_user_sigmask(sigmask, &sigsaved, ret == -ERESTARTNOHAND);
    ret = poll_select_copy_remaining(&end_time, tsp, type, ret);
-	restore_user_sigmask(sigmask, &sigsaved);
-
    return ret;
 }
@@ -1425,8 +1421,7 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time32, str
ret = do_sys_poll(ufds, nfds, to);
-	restore_user_sigmask(sigmask, &sigsaved);
-
+	restore_user_sigmask(sigmask, &sigsaved, ret == -EINTR);
    /* We can restart this syscall, usually */
    if (ret == -EINTR)
    	ret = -ERESTARTNOHAND;
@@ -1461,8 +1456,7 @@ COMPAT_SYSCALL_DEFINE5(ppoll_time64, str
ret = do_sys_poll(ufds, nfds, to);
-	restore_user_sigmask(sigmask, &sigsaved);
-
+	restore_user_sigmask(sigmask, &sigsaved, ret == -EINTR);
    /* We can restart this syscall, usually */
    if (ret == -EINTR)
    	ret = -ERESTARTNOHAND;
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -276,7 +276,7 @@ extern int sigprocmask(int, 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,
-				 sigset_t *sigsaved);
+				 sigset_t *sigsaved, bool interrupted);
 extern void set_current_blocked(sigset_t *);
 extern void __set_current_blocked(const sigset_t *);
 extern int show_unhandled_signals;
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2851,7 +2851,8 @@ EXPORT_SYMBOL(set_compat_user_sigmask);
  * 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)
+void restore_user_sigmask(const void __user *usigmask, sigset_t *sigsaved,
+				bool interrupted)
 {
if (!usigmask)
@@ -2861,7 +2862,7 @@ void restore_user_sigmask(const void __u
     * Restoring sigmask here can lead to delivering signals that the above
     * syscalls are intended to block because of the sigmask passed in.
     */
-	if (signal_pending(current)) {
+	if (interrupted) {
    	current->saved_sigmask = *sigsaved;
    	set_restore_sigmask();
    	return;

    

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[PATCH 5.1 02/96] signal: remove the wrong signal_pending() check in restore_user_sigmask()