linux-user: Check array bounds in errno conversion

Check array bounds in host_to_target_errno() and target_to_host_errno().

Signed-off-by: Timothy Edward Baldwin <T.E.Baldwin99@members.leeds.ac.uk>
Message-id: 1441497448-32489-2-git-send-email-T.E.Baldwin99@members.leeds.ac.uk
[PMM: Add a lower-bound check, use braces on if(), tweak commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>

linux-user/syscall.c

@@ -619,15 +619,19 @@ static uint16_t host_to_target_errno_table[ERRNO_TABLE_SIZE] = {
 
 static inline int host_to_target_errno(int err)
 {
-    if(host_to_target_errno_table[err])
+    if (err >= 0 && err < ERRNO_TABLE_SIZE &&
+        host_to_target_errno_table[err]) {
         return host_to_target_errno_table[err];
+    }
     return err;
 }
 
 static inline int target_to_host_errno(int err)
 {
-    if (target_to_host_errno_table[err])
+    if (err >= 0 && err < ERRNO_TABLE_SIZE &&
+        target_to_host_errno_table[err]) {
         return target_to_host_errno_table[err];
+    }
     return err;
 }