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

Greg Kroah-Hartman
2019-07-08T15:31:23Z

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;