Fix stack of librunas child by using mmap and a larger stack

Did cause SIGSEGV for tests/test_sessions.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/librunas/runas.c b/librunas/runas.c
index 1fc4116255b017ddeed25a2fa5dae414931b1e84..ba361d6d63156a3361816a83bc1c0ae1b3a692da 100644 (file)
--- a/librunas/runas.c
+++ b/librunas/runas.c
@@ -28,14 +28,11 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <sched.h>
+#include <sys/mman.h>
 
 #include <lttngerr.h>
 
-/*
- * We allocate a stack of twice this size and point in the middle of it
- * to support archs with stack growing up and down.
- */
-#define CHILD_STACK_SIZE 2048
+#define CHILD_STACK_SIZE       10485760
 
 struct run_as_data {
        int (*cmd)(void *data);
@@ -191,9 +188,9 @@ int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
        int ret = 0;
        int status;
        pid_t pid;
-       char *child_stack;
        int retval_pipe[2];
        ssize_t readlen, readleft, index;
+       void *child_stack;
        union {
                int i;
                char c[sizeof(int)];
@@ -210,10 +207,6 @@ int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
                }
        }
 
-       child_stack = malloc(CHILD_STACK_SIZE * 2);
-       if (!child_stack) {
-               return -ENOMEM;
-       }
        ret = pipe(retval_pipe);
        if (ret < 0) {
                perror("pipe");
@@ -224,13 +217,26 @@ int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
        run_as_data.uid = uid;
        run_as_data.gid = gid;
        run_as_data.retval_pipe = retval_pipe[1];       /* write end */
-
-       pid = clone(child_run_as, child_stack + CHILD_STACK_SIZE,
-               CLONE_FILES | SIGCHLD, &run_as_data, NULL);
+       child_stack = mmap(NULL, CHILD_STACK_SIZE,
+               PROT_WRITE | PROT_READ,
+               MAP_PRIVATE | MAP_GROWSDOWN | MAP_ANONYMOUS | MAP_STACK,
+               -1, 0);
+       if (child_stack == MAP_FAILED) {
+               perror("mmap");
+               ret = -ENOMEM;
+               goto close_pipe;
+       }
+       /*
+        * Pointing to the middle of the stack to support architectures
+        * where the stack grows up (HPPA).
+        */
+       pid = clone(child_run_as, child_stack + (CHILD_STACK_SIZE / 2),
+               CLONE_FILES | SIGCHLD,
+               &run_as_data, NULL);
        if (pid < 0) {
                perror("clone");
                ret = pid;
-               goto close_pipe;
+               goto unmap_stack;
        }
        /* receive return value */
        readleft = sizeof(retval);
@@ -255,11 +261,15 @@ int run_as(int (*cmd)(void *data), void *data, uid_t uid, gid_t gid)
                perror("wait");
                ret = -1;
        }
+unmap_stack:
+       ret = munmap(child_stack, CHILD_STACK_SIZE);
+       if (ret < 0) {
+               perror("munmap");
+       }
 close_pipe:
        close(retval_pipe[0]);
        close(retval_pipe[1]);
 end:
-       free(child_stack);
        return retval.i;
 }