Fix a malloc race condition involving strsignal.

A signal can arrive in the middle of a malloc, and Emacs's signal
handler can invoke strsignal, which can invoke malloc, which is
not portable.  This race condition bug makes Emacs hang on GNU/Linux.
Fix it by altering the signal handler so that it does not invoke
strsignal.
* emacs.c (shut_down_emacs): Use safe_strsignal, not strsignal.
* process.c (status_message): Use const pointer, in case strsignal
is #defined to safe_strsignal.
* sysdep.c (sys_siglist, init_signals): Always define and
initialize a substitute sys_siglist if the system does not define
one, even if HAVE_STRSIGNAL.
(safe_strsignal): Rename from strsignal.  Always define,
using sys_siglist.  Return a const pointer.
* syssignal.h (safe_strsignal): New decl.
(strsignal) [!HAVE_STRSIGNAL]: Define in terms of safe_strsignal.

1 files changed, 19 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index 7061038fdec..3a94af80c30 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,22 @@
+2012-10-01  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Fix a malloc race condition involving strsignal.
+        A signal can arrive in the middle of a malloc, and Emacs's signal
+        handler can invoke strsignal, which can invoke malloc, which is
+        not portable.  This race condition bug makes Emacs hang on GNU/Linux.
+        Fix it by altering the signal handler so that it does not invoke
+        strsignal.
+        * emacs.c (shut_down_emacs): Use safe_strsignal, not strsignal.
+        * process.c (status_message): Use const pointer, in case strsignal
+        is #defined to safe_strsignal.
+        * sysdep.c (sys_siglist, init_signals): Always define and
+        initialize a substitute sys_siglist if the system does not define
+        one, even if HAVE_STRSIGNAL.
+        (safe_strsignal): Rename from strsignal.  Always define,
+        using sys_siglist.  Return a const pointer.
+        * syssignal.h (safe_strsignal): New decl.
+        (strsignal) [!HAVE_STRSIGNAL]: Define in terms of safe_strsignal.
+
 2012-10-01  Eli Zaretskii  <eliz@gnu.org>
 
         * w32proc.c (timer_loop): Fix code that waits for timer