[PATCH 09/16] ptrace: In ptrace_setsiginfo deal with invalid si_signo

["Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>]

If the tracer calls PTRACE_SETSIGINFO it only has an effect if the
tracee is stopped in ptrace_signal.

When one of PTRACE_DETACH, PTRACE_SINGLESTEP, PTRACE_SINGLEBLOCK,
PTRACE_SYSEMU, PTRACE_SYSEMU_SINGLESTEP, PTRACE_SYSCALL, or
PTRACE_CONT pass in a signel number to continue with the kernel
validates that signal number and the ptrace_signal verifies the signal
number matches the si_signo, before the siginfo is used.

As the signal number to continue with is verified to be a valid signal
number the signal number in si_signo must be a valid signal number.

Make this obvious and avoid needing checks later by immediately
clearing siginfo if si_signo is not valid.

Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
 kernel/ptrace.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index a24eed725cec..a0a07d140751 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -716,7 +716,9 @@ static int ptrace_setsiginfo(struct task_struct *child, const kernel_siginfo_t *
 	if (unlikely(!child->last_siginfo))
 		return -EINVAL;
 
-	copy_siginfo(child->last_siginfo, info);
+	clear_siginfo(child->last_siginfo);
+	if (valid_signal(info->si_signo))
+		copy_siginfo(child->last_siginfo, info);
 	return 0;
 }
 
-- 
2.35.3