[PATCH] standalone shell / prefer_applets: fix comm field problem

[Lukasz Serafin]

The output of /proc/self/comm shall only be changed to the applet name
if it is "exe". It shall not be changed if it is for example the name
of a shell script.

Signed-off-by: Lukasz Serafin <lukasz.serafin at axis.com>
---
 include/libbb.h            |  2 ++
 libbb/appletlib.c          | 11 +++++++++--
 libbb/vfork_daemon_rexec.c |  5 +++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/include/libbb.h b/include/libbb.h
index 392c0443d..2e8d7f3d0 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1177,8 +1177,10 @@ void run_applet_no_and_exit(int a, const char *name, char **argv) NORETURN FAST_
 #endif
 #if defined(__linux__)
 void set_task_comm(const char *comm) FAST_FUNC;
+void get_task_comm(char *buffer) FAST_FUNC;
 #else
 # define set_task_comm(name) ((void)0)
+# define get_task_comm(name) ((void)0)
 #endif

 /* Helpers for daemonization.
diff --git a/libbb/appletlib.c b/libbb/appletlib.c
index f842e73cc..ad3affba4 100644
--- a/libbb/appletlib.c
+++ b/libbb/appletlib.c
@@ -33,6 +33,8 @@
 # include <malloc.h> /* for mallopt */
 #endif

+#define COMM_MAX_SIZE 16
+
 /* Declare <applet>_main() */
 #define PROTOTYPES
 #include "applets.h"
@@ -1115,8 +1117,13 @@ 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) {
+            char buffer[COMM_MAX_SIZE];
+            buffer[0] = '\0';
+            get_task_comm(buffer);
+            if (strcmp(buffer, "exe") == 0)
+                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 65271e84f..c12173cd0 100644
--- a/libbb/vfork_daemon_rexec.c
+++ b/libbb/vfork_daemon_rexec.c
@@ -33,6 +33,11 @@ void FAST_FUNC set_task_comm(const char *comm)
     /* okay if too long (truncates) */
     prctl(PR_SET_NAME, (long)comm, 0, 0, 0);
 }
+void FAST_FUNC get_task_comm(char* buffer)
+{
+    /* returned name can be up to 16 bytes long (including null byte) */
+    prctl(PR_GET_NAME, (long)buffer, 0, 0, 0);
+}
 #endif

 /*
--
2.11.0

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