linux-user: Block signals during sigaction() handling

Block signals while emulating sigaction. This is a non-interruptible
syscall, and using block_signals() avoids races where the host
signal handler is invoked and tries to examine the signal handler
data structures while we are updating them.

Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-29-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
[PMM: expanded commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>

1 files changed, 9 insertions, 3 deletions

diff --git a/linux-user/signal.c b/linux-user/signal.c
index f48902882d..b21d6bf625 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -640,7 +640,7 @@ out:
     return ret;
 }
 
-/* do_sigaction() return host values and errnos */
+/* do_sigaction() return target values and host errnos */
 int do_sigaction(int sig, const struct target_sigaction *act,
                  struct target_sigaction *oact)
 {
@@ -649,8 +649,14 @@ int do_sigaction(int sig, const struct target_sigaction *act,
     int host_sig;
     int ret = 0;
 
-    if (sig < 1 || sig > TARGET_NSIG || sig == TARGET_SIGKILL || sig == TARGET_SIGSTOP)
-        return -EINVAL;
+    if (sig < 1 || sig > TARGET_NSIG || sig == TARGET_SIGKILL || sig == TARGET_SIGSTOP) {
+        return -TARGET_EINVAL;
+    }
+
+    if (block_signals()) {
+        return -TARGET_ERESTARTSYS;
+    }
+
     k = &sigact_table[sig - 1];
     if (oact) {
         __put_user(k->_sa_handler, &oact->_sa_handler);