[PATCH v3 08/16] Warn when attempting to log in a signal unsafe manner from signal context

[Chase Douglas]

Also, print out the offending message format. This will hopefully help
developers track down unsafe logging.

Signed-off-by: Chase Douglas <chase.douglas at canonical.com>
---
 os/log.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/os/log.c b/os/log.c
index 3747fe0..36e678e 100644
--- a/os/log.c
+++ b/os/log.c
@@ -352,6 +352,16 @@ LogVWrite(int verb, const char *f, va_list args)
     int len = 0;
     static Bool newline = TRUE;
 
+    if (inSignalContext) {
+        BUG_WARN_MSG(inSignalContext,
+                     "Warning: attempting to log data in a signal unsafe "
+                     "manner while in signal context. Please update to check "
+                     "inSignalContext and/or use LogMessageVerbSigSafe() or "
+                     "ErrorSigSafe(). The offending log format message is: "
+                     "%s\n", f);
+        return;
+    }
+
     if (newline) {
         sprintf(tmpBuffer, "[%10.3f] ", GetTimeInMillis() / 1000.0);
         len = strlen(tmpBuffer);
@@ -578,6 +588,22 @@ LogVHdrMessageVerb(MessageType type, int verb, const char *msg_format,
     char *p;
     int left;
 
+    if (inSignalContext) {
+        static const char warning[] = "Warning: attempting to log data in a "
+                                      "signal unsafe manner while in signal "
+                                      "context. Please update to check "
+                                      "inSignalContext and/or use "
+                                      "LogMessageVerbSigSafe(). The offending "
+                                      "header and log message formats are:\n";
+
+        write(logFileFd, warning, sizeof(warning) - 1);
+
+        write(logFileFd, hdr_format, strlen_sigsafe(hdr_format));
+        write(logFileFd, msg_format, strlen_sigsafe(msg_format));
+
+        return;
+    }
+
     type_str = LogMessageTypeVerbString(type, verb);
     if (!type_str)
         return;
-- 
1.7.9.1