[PATCH 6.18 301/752] um: Preserve errno within signal handler

Sasha Levin
2026-02-28T17:52:20Z

From: Tiwei Bie <tiwei.btw@antgroup.com>

[ Upstream commit f68b2d5a907b53eed99cf2efcaaae116df73c298 ]

We rely on errno to determine whether a syscall has failed, so we
need to ensure that accessing errno is async-signal-safe. Currently,
we preserve the errno in sig_handler_common(), but it doesn't cover
every possible case. Let's do it in hard_handler() instead, which
is the signal handler we actually register.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20260106001228.1531146-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/um/os-Linux/signal.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/um/os-Linux/signal.c b/arch/um/os-Linux/signal.c
index 11f07f4982700..bebeb6b4bee8b 100644
--- a/arch/um/os-Linux/signal.c
+++ b/arch/um/os-Linux/signal.c
@@ -35,7 +35,6 @@ void (*sig_info[NSIG])(int, struct siginfo *, struct uml_pt_regs *, void *mc) =
static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
{
struct uml_pt_regs r;
- int save_errno = errno;

r.is_user = 0;
if (sig == SIGSEGV) {
@@ -49,8 +48,6 @@ static void sig_handler_common(int sig, struct siginfo *si, mcontext_t *mc)
unblock_signals_trace();

(*sig_info[sig])(sig, si, &r, mc);
-
- errno = save_errno;
}

/*
@@ -201,8 +198,11 @@ static void hard_handler(int sig, siginfo_t *si, void *p)
{
ucontext_t *uc = p;
mcontext_t *mc = &uc->uc_mcontext;
+ int save_errno = errno;

(*handlers[sig])(sig, (struct siginfo *)si, mc);
+
+ errno = save_errno;
}

void set_handler(int sig)
--
2.51.0