string: strerror, strsignal cannot use buffer after dlmopen (bug 32026)

Secondary namespaces have a different malloc.  Allocating the
buffer in one namespace and freeing it another results in
heap corruption.  Fix this by using a static string (potentially
translated) in secondary namespaces.  It would also be possible
to use the malloc from the initial namespace to manage the
buffer, but these functions would still not be safe to use in
auditors etc. because a call to strerror could still free a
buffer while it is used by the application.  Another approach
could use proper initial-exec TLS, duplicated in secondary
namespaces, but that would need a callback interface for freeing
libc resources in namespaces on thread exit, which does not exist
today.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

1 files changed, 22 insertions, 14 deletions

diff --git a/string/strsignal.c b/string/strsignal.c
index 3114601..d9b0365 100644
--- a/string/strsignal.c
+++ b/string/strsignal.c
@@ -21,6 +21,7 @@
 #include <string.h>
 #include <libintl.h>
 #include <tls-internal.h>
+#include <libc-internal.h>
 
 /* Return a string describing the meaning of the signal number SIGNUM.  */
 char *
@@ -30,21 +31,28 @@ strsignal (int signum)
   if (desc != NULL)
     return _(desc);
 
-  struct tls_internal_t *tls_internal = __glibc_tls_internal ();
-  free (tls_internal->strsignal_buf);
+  if (__libc_initial)
+    {
+      struct tls_internal_t *tls_internal = __glibc_tls_internal ();
+      free (tls_internal->strsignal_buf);
 
-  int r;
+      int r;
 #ifdef SIGRTMIN
-  if (signum >= SIGRTMIN && signum <= SIGRTMAX)
-    r = __asprintf (&tls_internal->strsignal_buf, _("Real-time signal %d"),
-		    signum - SIGRTMIN);
-  else
+      if (signum >= SIGRTMIN && signum <= SIGRTMAX)
+	r = __asprintf (&tls_internal->strsignal_buf, _("Real-time signal %d"),
+			signum - SIGRTMIN);
+      else
 #endif
-    r = __asprintf (&tls_internal->strsignal_buf, _("Unknown signal %d"),
-		    signum);
-
-  if (r == -1)
-    tls_internal->strsignal_buf = NULL;
-
-  return tls_internal->strsignal_buf;
+	r = __asprintf (&tls_internal->strsignal_buf, _("Unknown signal %d"),
+			signum);
+
+      if (r >= 0)
+	return tls_internal->strsignal_buf;
+      else
+	tls_internal->strsignal_buf = NULL;
+    }
+  /* Fall through on asprintf error, and for !__libc_initial:
+     secondary namespaces use a different malloc and cannot
+     participate in the buffer management.  */
+  return _("Unknown signal");
 }