[uml-user] [RFC PATCH 4/10] SKAS4 - Work around compat PTRACE_GETSIGINFO bug

[Jeff D. <jd...@ad...>]

copy_siginfo_to_user correctly strips off the high bits of si->si_code
before copying it to userspace.

Unfortunately, ptrace32_siginfo calls copy_siginfo_to_user to put the
siginfo into a temporary userspace buffer and counts on the high bits
still being present so that it may initialize the union in the final
32-bit siginfo.

This patch works around this problem by having copy_siginfo_to_user
copy si->si_code intact to userspace.  This introduces a bug in native
64-bit PTRACE_GETSIGINFO, but I haven't noticed anything being
bothered by it.

diff --git a/kernel/signal.c b/kernel/signal.c
index 1e067a1..28813b1 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2088,7 +2088,7 @@ int copy_siginfo_to_user(siginfo_t __user *to, siginfo_t *from)
 	 */
 	err = __put_user(from->si_signo, &to->si_signo);
 	err |= __put_user(from->si_errno, &to->si_errno);
-	err |= __put_user((short)from->si_code, &to->si_code);
+	err |= __put_user(from->si_code, &to->si_code);
 	switch (from->si_code & __SI_MASK) {
 	case __SI_KILL:
 		err |= __put_user(from->si_pid, &to->si_pid);