| From 22b838ede92e4da81dbde1d18672d9f9c6ac2900 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Fri, 16 Aug 2019 12:33:54 -0500 |
| Subject: signal: Allow cifs and drbd to receive their terminating signals |
| MIME-Version: 1.0 |
| Content-Type: text/plain; charset=UTF-8 |
| Content-Transfer-Encoding: 8bit |
| |
| From: Eric W. Biederman <ebiederm@xmission.com> |
| |
| [ Upstream commit 33da8e7c814f77310250bb54a9db36a44c5de784 ] |
| |
| My recent to change to only use force_sig for a synchronous events |
| wound up breaking signal reception cifs and drbd. I had overlooked |
| the fact that by default kthreads start out with all signals set to |
| SIG_IGN. So a change I thought was safe turned out to have made it |
| impossible for those kernel thread to catch their signals. |
| |
| Reverting the work on force_sig is a bad idea because what the code |
| was doing was very much a misuse of force_sig. As the way force_sig |
| ultimately allowed the signal to happen was to change the signal |
| handler to SIG_DFL. Which after the first signal will allow userspace |
| to send signals to these kernel threads. At least for |
| wake_ack_receiver in drbd that does not appear actively wrong. |
| |
| So correct this problem by adding allow_kernel_signal that will allow |
| signals whose siginfo reports they were sent by the kernel through, |
| but will not allow userspace generated signals, and update cifs and |
| drbd to call allow_kernel_signal in an appropriate place so that their |
| thread can receive this signal. |
| |
| Fixing things this way ensures that userspace won't be able to send |
| signals and cause problems, that it is clear which signals the |
| threads are expecting to receive, and it guarantees that nothing |
| else in the system will be affected. |
| |
| This change was partly inspired by similar cifs and drbd patches that |
| added allow_signal. |
| |
| Reported-by: ronnie sahlberg <ronniesahlberg@gmail.com> |
| Reported-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com> |
| Tested-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com> |
| Cc: Steve French <smfrench@gmail.com> |
| Cc: Philipp Reisner <philipp.reisner@linbit.com> |
| Cc: David Laight <David.Laight@ACULAB.COM> |
| Fixes: 247bc9470b1e ("cifs: fix rmmod regression in cifs.ko caused by force_sig changes") |
| Fixes: 72abe3bcf091 ("signal/cifs: Fix cifs_put_tcp_session to call send_sig instead of force_sig") |
| Fixes: fee109901f39 ("signal/drbd: Use send_sig not force_sig") |
| Fixes: 3cf5d076fb4d ("signal: Remove task parameter from force_sig") |
| Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| drivers/block/drbd/drbd_main.c | 2 ++ |
| fs/cifs/connect.c | 2 +- |
| include/linux/signal.h | 15 ++++++++++++++- |
| kernel/signal.c | 5 +++++ |
| 4 files changed, 22 insertions(+), 2 deletions(-) |
| |
| diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c |
| index f5c24459fc5c1..daa9cef96ec66 100644 |
| --- a/drivers/block/drbd/drbd_main.c |
| +++ b/drivers/block/drbd/drbd_main.c |
| @@ -332,6 +332,8 @@ static int drbd_thread_setup(void *arg) |
| thi->name[0], |
| resource->name); |
| |
| + allow_kernel_signal(DRBD_SIGKILL); |
| + allow_kernel_signal(SIGXCPU); |
| restart: |
| retval = thi->function(thi); |
| |
| diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c |
| index 7d46025d5e899..751bdde6515d5 100644 |
| --- a/fs/cifs/connect.c |
| +++ b/fs/cifs/connect.c |
| @@ -885,7 +885,7 @@ cifs_demultiplex_thread(void *p) |
| mempool_resize(cifs_req_poolp, length + cifs_min_rcv); |
| |
| set_freezable(); |
| - allow_signal(SIGKILL); |
| + allow_kernel_signal(SIGKILL); |
| while (server->tcpStatus != CifsExiting) { |
| if (try_to_freeze()) |
| continue; |
| diff --git a/include/linux/signal.h b/include/linux/signal.h |
| index 5308304993bea..ffa58ff53e225 100644 |
| --- a/include/linux/signal.h |
| +++ b/include/linux/signal.h |
| @@ -313,6 +313,9 @@ extern void signal_setup_done(int failed, struct ksignal *ksig, int stepping); |
| extern void exit_signals(struct task_struct *tsk); |
| extern void kernel_sigaction(int, __sighandler_t); |
| |
| +#define SIG_KTHREAD ((__force __sighandler_t)2) |
| +#define SIG_KTHREAD_KERNEL ((__force __sighandler_t)3) |
| + |
| static inline void allow_signal(int sig) |
| { |
| /* |
| @@ -320,7 +323,17 @@ static inline void allow_signal(int sig) |
| * know it'll be handled, so that they don't get converted to |
| * SIGKILL or just silently dropped. |
| */ |
| - kernel_sigaction(sig, (__force __sighandler_t)2); |
| + kernel_sigaction(sig, SIG_KTHREAD); |
| +} |
| + |
| +static inline void allow_kernel_signal(int sig) |
| +{ |
| + /* |
| + * Kernel threads handle their own signals. Let the signal code |
| + * know signals sent by the kernel will be handled, so that they |
| + * don't get silently dropped. |
| + */ |
| + kernel_sigaction(sig, SIG_KTHREAD_KERNEL); |
| } |
| |
| static inline void disallow_signal(int sig) |
| diff --git a/kernel/signal.c b/kernel/signal.c |
| index 30914b3c76b21..57fadbe69c2e6 100644 |
| --- a/kernel/signal.c |
| +++ b/kernel/signal.c |
| @@ -79,6 +79,11 @@ static int sig_task_ignored(struct task_struct *t, int sig, bool force) |
| handler == SIG_DFL && !(force && sig_kernel_only(sig))) |
| return 1; |
| |
| + /* Only allow kernel generated signals to this kthread */ |
| + if (unlikely((t->flags & PF_KTHREAD) && |
| + (handler == SIG_KTHREAD_KERNEL) && !force)) |
| + return true; |
| + |
| return sig_handler_ignored(handler, sig); |
| } |
| |
| -- |
| 2.20.1 |
| |