shell: fix script's comm field if ENABLE_FEATURE_PREFER_APPLETS=y

function                                             old     new   delta
re_execed_comm                                         -      46     +46
main                                                  72      86     +14
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 1/0 up/down: 60/0)               Total: 60 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 24 insertions, 2 deletions

diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index e8c308467..03389f541 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -1112,8 +1112,14 @@ int main(int argc UNUSED_PARAM, char **argv)
          || ENABLE_FEATURE_PREFER_APPLETS
          || !BB_MMU
         ) {
-                if (NUM_APPLETS > 1)
-                        set_task_comm(applet_name);
+                if (NUM_APPLETS > 1) {
+                        /* Careful, do not trash comm of "SCRIPT.sh" -
+                         * the case when started from e.g. #!/bin/ash script.
+                         * (not limited to shells - #!/bin/awk scripts also exist)
+                         */
+                        if (re_execed_comm())
+                                set_task_comm(applet_name);
+                }
         }
 
         parse_config_file(); /* ...maybe, if FEATURE_SUID_CONFIG */
diff --git a/libbb/vfork_daemon_rexec.c b/libbb/vfork_daemon_rexec.c
index a49fe8e01..31e97051f 100644
--- a/libbb/vfork_daemon_rexec.c
+++ b/libbb/vfork_daemon_rexec.c
@@ -28,6 +28,22 @@
 # ifndef PR_GET_NAME
 # define PR_GET_NAME 16
 # endif
+# if ENABLE_FEATURE_SH_STANDALONE || ENABLE_FEATURE_PREFER_APPLETS || !BB_MMU
+int FAST_FUNC re_execed_comm(void)
+{
+        const char *e, *expected_comm;
+        char comm[16];
+
+        BUILD_BUG_ON(CONFIG_BUSYBOX_EXEC_PATH[0] != '/');
+        e = CONFIG_BUSYBOX_EXEC_PATH;
+        /* Hopefully (strrchr(e) - e) evaluates to constant at compile time: */
+        expected_comm = bb_busybox_exec_path + (strrchr(e, '/') - e) + 1;
+
+        prctl(PR_GET_NAME, (long)comm, 0, 0, 0);
+        //bb_error_msg("comm:'%.*s' expected:'%s'", 16, comm, expected_comm);
+        return strcmp(comm, expected_comm) == 0;
+}
+# endif
 void FAST_FUNC set_task_comm(const char *comm)
 {
         /* okay if too long (truncates) */