[tor-commits] [tor/master] Use format_hex_number_sigsafe to format syscalls in sandbox.c

[nickm at torproject.org]

commit 85178e2e93036d0708bafa431fcdf4c1029ad2ff
Author: Nick Mathewson <nickm at torproject.org>
Date:   Mon Jul 15 13:07:09 2013 -0400

    Use format_hex_number_sigsafe to format syscalls in sandbox.c
    
    This way, we don't have to use snprintf, which is not guaranteed to
    be signal-safe.
    
    (Technically speaking, strlen() and strlcpy() are not guaranteed to
    be signal-safe by the POSIX standard. But I claim that they are on
    every platform that supports libseccomp2, which is what matters
    here.)
---
 src/common/sandbox.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/common/sandbox.c b/src/common/sandbox.c
index 68be89e..dbb1657 100644
--- a/src/common/sandbox.c
+++ b/src/common/sandbox.c
@@ -13,9 +13,10 @@
 #include <string.h>
 #include <stdlib.h>
 
+#include "orconfig.h"
 #include "sandbox.h"
 #include "torlog.h"
-#include "orconfig.h"
+#include "util.h"
 
 #if defined(HAVE_SECCOMP_H) && defined(__linux__)
 #define USE_LIBSECCOMP
@@ -202,7 +203,7 @@ static void
 sigsys_debugging(int nr, siginfo_t *info, void *void_context)
 {
   ucontext_t *ctx = (ucontext_t *) (void_context);
-  char message[64];
+  char message[256];
   int rv = 0, syscall, length, err;
   (void) nr;
 
@@ -214,11 +215,12 @@ sigsys_debugging(int nr, siginfo_t *info, void *void_context)
 
   syscall = ctx->uc_mcontext.gregs[REG_SYSCALL];
 
-  /* XXXX Avoid use of snprintf; it isn't on the list of Stuff You're Allowed
-   * To Do In A Signal Handler. */
-  length = snprintf(message, sizeof(message),
-      "\n\n(Sandbox) bad syscall (%d) was caught.\n",
-      syscall);
+  strlcpy(message, "\n\n(Sandbox) Caught a bad syscall attempt (syscall 0x",
+          sizeof(message));
+  (void) format_hex_number_sigsafe(syscall, message+strlen(message),
+                                   sizeof(message)-strlen(message));
+  strlcat(message, ")\n", sizeof(message));
+  length = strlen(message);
 
   err = 0;
   if (sigsys_debugging_fd >= 0) {