[PULL 3/5] linux-user: fix TARGET_NSIG and _NSIG uses

[Laurent Vivier <laurent@vivier.eu>]

Valid signal numbers are between 1 (SIGHUP) and SIGRTMAX.

System includes define _NSIG to SIGRTMAX + 1, but
QEMU (like kernel) defines TARGET_NSIG to TARGET_SIGRTMAX.

Fix all the checks involving the signal range.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Taylor Simpson <tsimpson@quicinc.com>
Message-Id: <20200212125658.644558-4-laurent@vivier.eu>
---
 linux-user/signal.c | 52 ++++++++++++++++++++++++++++++++-------------
 1 file changed, 37 insertions(+), 15 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 246315571c09..c1e664f97a7c 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -30,6 +30,15 @@ static struct target_sigaction sigact_table[TARGET_NSIG];
 static void host_signal_handler(int host_signum, siginfo_t *info,
                                 void *puc);
 
+
+/*
+ * System includes define _NSIG as SIGRTMAX + 1,
+ * but qemu (like the kernel) defines TARGET_NSIG as TARGET_SIGRTMAX
+ * and the first signal is SIGHUP defined as 1
+ * Signal number 0 is reserved for use as kill(pid, 0), to test whether
+ * a process exists without sending it a signal.
+ */
+QEMU_BUILD_BUG_ON(__SIGRTMAX + 1 != _NSIG);
 static uint8_t host_to_target_signal_table[_NSIG] = {
     [SIGHUP] = TARGET_SIGHUP,
     [SIGINT] = TARGET_SIGINT,
@@ -67,19 +76,24 @@ static uint8_t host_to_target_signal_table[_NSIG] = {
     [SIGSYS] = TARGET_SIGSYS,
     /* next signals stay the same */
 };
-static uint8_t target_to_host_signal_table[_NSIG];
 
+static uint8_t target_to_host_signal_table[TARGET_NSIG + 1];
+
+/* valid sig is between 1 and _NSIG - 1 */
 int host_to_target_signal(int sig)
 {
-    if (sig < 0 || sig >= _NSIG)
+    if (sig < 1 || sig >= _NSIG) {
         return sig;
+    }
     return host_to_target_signal_table[sig];
 }
 
+/* valid sig is between 1 and TARGET_NSIG */
 int target_to_host_signal(int sig)
 {
-    if (sig < 0 || sig >= _NSIG)
+    if (sig < 1 || sig > TARGET_NSIG) {
         return sig;
+    }
     return target_to_host_signal_table[sig];
 }
 
@@ -100,11 +114,15 @@ static inline int target_sigismember(const target_sigset_t *set, int signum)
 void host_to_target_sigset_internal(target_sigset_t *d,
                                     const sigset_t *s)
 {
-    int i;
+    int host_sig, target_sig;
     target_sigemptyset(d);
-    for (i = 1; i <= TARGET_NSIG; i++) {
-        if (sigismember(s, i)) {
-            target_sigaddset(d, host_to_target_signal(i));
+    for (host_sig = 1; host_sig < _NSIG; host_sig++) {
+        target_sig = host_to_target_signal(host_sig);
+        if (target_sig < 1 || target_sig > TARGET_NSIG) {
+            continue;
+        }
+        if (sigismember(s, host_sig)) {
+            target_sigaddset(d, target_sig);
         }
     }
 }
@@ -122,11 +140,15 @@ void host_to_target_sigset(target_sigset_t *d, const sigset_t *s)
 void target_to_host_sigset_internal(sigset_t *d,
                                     const target_sigset_t *s)
 {
-    int i;
+    int host_sig, target_sig;
     sigemptyset(d);
-    for (i = 1; i <= TARGET_NSIG; i++) {
-        if (target_sigismember(s, i)) {
-            sigaddset(d, target_to_host_signal(i));
+    for (target_sig = 1; target_sig <= TARGET_NSIG; target_sig++) {
+        host_sig = target_to_host_signal(target_sig);
+        if (host_sig < 1 || host_sig >= _NSIG) {
+            continue;
+        }
+        if (target_sigismember(s, target_sig)) {
+            sigaddset(d, host_sig);
         }
     }
 }
@@ -492,10 +514,10 @@ static void signal_table_init(void)
         if (host_to_target_signal_table[host_sig] == 0) {
             host_to_target_signal_table[host_sig] = host_sig;
         }
-    }
-    for (host_sig = 1; host_sig < _NSIG; host_sig++) {
         target_sig = host_to_target_signal_table[host_sig];
-        target_to_host_signal_table[target_sig] = host_sig;
+        if (target_sig <= TARGET_NSIG) {
+            target_to_host_signal_table[target_sig] = host_sig;
+        }
     }
 }
 
@@ -518,7 +540,7 @@ void signal_init(void)
     act.sa_sigaction = host_signal_handler;
     for(i = 1; i <= TARGET_NSIG; i++) {
 #ifdef TARGET_GPROF
-        if (i == SIGPROF) {
+        if (i == TARGET_SIGPROF) {
             continue;
         }
 #endif
-- 
2.24.1