[tor-commits] [tor/master] Use prctl() to have the kernel SIGTERM background processes on exit.

[nickm at torproject.org]

commit fa81508eb2d9a2a2ea69c2c585735aef7aaff97c
Author: Yawning Angel <yawning at schwanenlied.me>
Date:   Thu Mar 26 14:56:14 2015 +0000

    Use prctl() to have the kernel SIGTERM background processes on exit.
    
    This uses a Linux-ism to attempt to always clean up background processes
    if possible.  Note that it is not a catch-all, in that executables with
    suid/sgid or elevated capabilities will have the prctl() attribute
    stripped as part of the execve().
    
    Resolves ticket 15471.
---
 changes/feature15471 |    5 +++++
 src/common/util.c    |   18 ++++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/changes/feature15471 b/changes/feature15471
new file mode 100644
index 0000000..594adf0
--- /dev/null
+++ b/changes/feature15471
@@ -0,0 +1,5 @@
+  o Minor features (pluggable transports):
+    - When launching managed pluggable transports on linux systems,
+      attempt to have the kernel deliver a SIGTERM on tor exit if
+      the pluggable transport process is still running. Resolves
+      ticket 15471.
diff --git a/src/common/util.c b/src/common/util.c
index 2c3a1a1..246a0d3 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -95,6 +95,9 @@
 #ifdef HAVE_SYS_WAIT_H
 #include <sys/wait.h>
 #endif
+#if defined(HAVE_SYS_PRCTL_H) && defined(__linux__)
+#include <sys/prctl.h>
+#endif
 
 #ifdef __clang_analyzer__
 #undef MALLOC_ZERO_WORKS
@@ -4180,6 +4183,15 @@ tor_spawn_background(const char *const filename, const char **argv,
   if (0 == pid) {
     /* In child */
 
+#if defined(HAVE_SYS_PRCTL_H) && defined(__linux__)
+    /* Attempt to have the kernel issue a SIGTERM if the parent
+     * goes away. Certain attributes of the binary being execve()ed
+     * will clear this during the execve() call, but it's better
+     * than nothing.
+     */
+    prctl(PR_SET_PDEATHSIG, SIGTERM);
+#endif
+
     child_state = CHILD_STATE_DUPOUT;
 
     /* Link child stdout to the write end of the pipe */
@@ -4225,8 +4237,10 @@ tor_spawn_background(const char *const filename, const char **argv,
        does not modify the arguments */
     if (env)
       execve(filename, (char *const *) argv, env->unixoid_environment_block);
-    else
-      execvp(filename, (char *const *) argv);
+    else {
+      static char *new_env[] = { NULL };
+      execve(filename, (char *const *) argv, new_env);
+    }
 
     /* If we got here, the exec or open(/dev/null) failed */