From: Eric W. Biederman Date: Tue, 5 Feb 2019 13:19:11 +0000 (-0600) Subject: signal: Always attempt to allocate siginfo for SIGSTOP X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a692933a87691681e880feb708081681ff32400a;p=openwrt%2Fstaging%2Fblogic.git signal: Always attempt to allocate siginfo for SIGSTOP Since 2.5.34 the code has had the potential to not allocate siginfo for SIGSTOP signals. Except for ptrace this is perfectly fine as only ptrace can use PTRACE_PEEK_SIGINFO and see what the contents of the delivered siginfo are. Users of PTRACE_PEEK_SIGINFO that care about the contents siginfo for SIGSTOP are rare, but they do exist. A seccomp self test has cared and lldb cares. Jack Andersen writes: > The patch titled > `signal: Never allocate siginfo for SIGKILL or SIGSTOP` > created a regression for users of PTRACE_GETSIGINFO needing to > discern signals that were raised via the tgkill syscall. > > A notable user of this tgkill+ptrace combination is lldb while > debugging a multithreaded program. Without the ability to detect a > SIGSTOP originating from tgkill, lldb does not have a way to > synchronize on a per-thread basis and falls back to SIGSTOP-ing the > entire process. Everyone affected by this please note. The kernel can still fail to allocate a siginfo structure. The allocation is with GFP_KERNEL and is best effort only. If memory is tight when the signal allocation comes in this will fail to allocate a siginfo. So I strongly recommend looking at more robust solutions for synchronizing with a single thread such as PTRACE_INTERRUPT. Or if that does not work persuading your friendly local kernel developer to build the interface you need. Reported-by: Tycho Andersen Reported-by: Kees Cook Reported-by: Jack Andersen Acked-by: Linus Torvalds Reviewed-by: Christian Brauner Cc: stable@vger.kernel.org Fixes: f149b3155744 ("signal: Never allocate siginfo for SIGKILL or SIGSTOP") Fixes: 6dfc88977e42 ("[PATCH] shared thread signals") History Tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git Signed-off-by: "Eric W. Biederman" --- diff --git a/kernel/signal.c b/kernel/signal.c index e1d7ad8e6ab1..9ca8e5278c8e 100644 --- a/kernel/signal.c +++ b/kernel/signal.c @@ -1057,10 +1057,9 @@ static int __send_signal(int sig, struct kernel_siginfo *info, struct task_struc result = TRACE_SIGNAL_DELIVERED; /* - * Skip useless siginfo allocation for SIGKILL SIGSTOP, - * and kernel threads. + * Skip useless siginfo allocation for SIGKILL and kernel threads. */ - if (sig_kernel_only(sig) || (t->flags & PF_KTHREAD)) + if ((sig == SIGKILL) || (t->flags & PF_KTHREAD)) goto out_set; /*