On Mon, Nov 22, 2021 at 4:31 AM gregkh@linuxfoundation.org wrote:
The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From e349d945fac76bddc78ae1cb92a0145b427a87ce Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" ebiederm@xmission.com Date: Thu, 18 Nov 2021 11:11:13 -0600 Subject: [PATCH] signal: Don't always set SA_IMMUTABLE for forced signals
Recently to prevent issues with SECCOMP_RET_KILL and similar signals being changed before they are delivered SA_IMMUTABLE was added.
Unfortunately this broke debuggers[1][2] which reasonably expect to be able to trap synchronous SIGTRAP and SIGSEGV even when the target process is not configured to handle those signals.
Update force_sig_to_task to support both the case when we can allow the debugger to intercept and possibly ignore the signal and the case when it is not safe to let userspace know about the signal until the process has exited.
Suggested-by: Linus Torvalds torvalds@linux-foundation.org Reported-by: Kyle Huey me@kylehuey.com Reported-by: kernel test robot oliver.sang@intel.com Cc: stable@vger.kernel.org [1] https://lkml.kernel.org/r/CAP045AoMY4xf8aC_4QU_-j7obuEPYgTcnQQP3Yxk=2X90jtpj... [2] https://lkml.kernel.org/r/20211117150258.GB5403@xsang-OptiPlex-9020 Fixes: 00b06da29cf9 ("signal: Add SA_IMMUTABLE to ensure forced siganls do not get changed") Link: https://lkml.kernel.org/r/877dd5qfw5.fsf_-_@email.froward.int.ebiederm.org Reviewed-by: Kees Cook keescook@chromium.org Tested-by: Kees Cook keescook@chromium.org Tested-by: Kyle Huey khuey@kylehuey.com Signed-off-by: "Eric W. Biederman" ebiederm@xmission.com
diff --git a/kernel/signal.c b/kernel/signal.c index 7c4b7ae714d4..7815e1bbeddc 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1298,6 +1298,12 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p return ret; }
+enum sig_handler {
HANDLER_CURRENT, /* If reachable use the current handler */HANDLER_SIG_DFL, /* Always use SIG_DFL handler semantics */HANDLER_EXIT, /* Only visible as the process exit code */+};
/*
- Force a signal that the process can't ignore: if necessary
- we unblock the signal and change any SIG_IGN to SIG_DFL.
@@ -1310,7 +1316,8 @@ int do_send_sig_info(int sig, struct kernel_siginfo *info, struct task_struct *p
- that is why we also clear SIGNAL_UNKILLABLE.
*/ static int -force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool sigdfl) +force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t,
enum sig_handler handler){ unsigned long int flags; int ret, blocked, ignored; @@ -1321,9 +1328,10 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool action = &t->sighand->action[sig-1]; ignored = action->sa.sa_handler == SIG_IGN; blocked = sigismember(&t->blocked, sig);
if (blocked || ignored || sigdfl) {
if (blocked || ignored || (handler != HANDLER_CURRENT)) { action->sa.sa_handler = SIG_DFL;
action->sa.sa_flags |= SA_IMMUTABLE;
if (handler == HANDLER_EXIT)action->sa.sa_flags |= SA_IMMUTABLE; if (blocked) { sigdelset(&t->blocked, sig); recalc_sigpending_and_wake(t);@@ -1343,7 +1351,7 @@ force_sig_info_to_task(struct kernel_siginfo *info, struct task_struct *t, bool
int force_sig_info(struct kernel_siginfo *info) {
return force_sig_info_to_task(info, current, false);
return force_sig_info_to_task(info, current, HANDLER_CURRENT);}
/* @@ -1660,7 +1668,7 @@ void force_fatal_sig(int sig) info.si_code = SI_KERNEL; info.si_pid = 0; info.si_uid = 0;
force_sig_info_to_task(&info, current, true);
force_sig_info_to_task(&info, current, HANDLER_SIG_DFL);}
/* @@ -1693,7 +1701,7 @@ int force_sig_fault_to_task(int sig, int code, void __user *addr info.si_flags = flags; info.si_isr = isr; #endif
return force_sig_info_to_task(&info, t, false);
return force_sig_info_to_task(&info, t, HANDLER_CURRENT);}
int force_sig_fault(int sig, int code, void __user *addr @@ -1813,7 +1821,8 @@ int force_sig_seccomp(int syscall, int reason, bool force_coredump) info.si_errno = reason; info.si_arch = syscall_get_arch(current); info.si_syscall = syscall;
return force_sig_info_to_task(&info, current, force_coredump);
return force_sig_info_to_task(&info, current,force_coredump ? HANDLER_EXIT : HANDLER_CURRENT);}
/* For the crazy architectures that include trap information in
Since this is taken care of now, AFAICT, I do have one additional question. I reported the regression to LKML a day or so before 5.15.3 was cut. What should I have noticed to see that the regressing changeset was going to 5.15 and where should I have said "hey please don't ship this on 5.15 yet"?
I'd like to know what to do next time :)
- Kyle