[PATCH] exec: Force binary name when argv is empty

From: Ren Zhijie
Date: Tue Sep 20 2022 - 08:12:42 EST


From: Hui Tang <tanghui20@xxxxxxxxxx>

First run './execv-main execv-child', there is empty in 'COMMAND' column
when run 'ps -u'.

USER PID %CPU %MEM VSZ RSS TTY [...] TIME COMMAND
root 368 0.3 0.0 4388 764 ttyS0 0:00 ./execv-main
root 369 0.6 0.0 4520 812 ttyS0 0:00

The program 'execv-main' as follows:

int main(int argc, char **argv)
{
char *execv_argv[] = {NULL};
pid_t pid = fork();

if (pid == 0) {
execv(argv[1], execv_argv);
} else if (pid > 0) {
wait(NULL);
}
return 0;
}

So replace empty string ("") added with the name of binary
when calling execve with a NULL argv.

Fixes: dcd46d897adb ("exec: Force single empty string when argv is empty")
Signed-off-by: Hui Tang <tanghui20@xxxxxxxxxx>
---
fs/exec.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 939d76e23935..7d1909a89a57 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -494,8 +494,8 @@ static int bprm_stack_limits(struct linux_binprm *bprm)
* signal to the parent that the child has run out of stack space.
* Instead, calculate it here so it's possible to fail gracefully.
*
- * In the case of argc = 0, make sure there is space for adding a
- * empty string (which will bump argc to 1), to ensure confused
+ * In the case of argc = 0, make sure there is space for adding
+ * bprm->filename (which will bump argc to 1), to ensure confused
* userspace programs don't start processing from argv[1], thinking
* argc can never be 0, to keep them from walking envp by accident.
* See do_execveat_common().
@@ -1900,7 +1900,7 @@ static int do_execveat_common(int fd, struct filename *filename,

retval = count(argv, MAX_ARG_STRINGS);
if (retval == 0)
- pr_warn_once("process '%s' launched '%s' with NULL argv: empty string added\n",
+ pr_warn_once("process '%s' launched '%s' with NULL argv: bprm->filename added\n",
current->comm, bprm->filename);
if (retval < 0)
goto out_free;
@@ -1929,13 +1929,13 @@ static int do_execveat_common(int fd, struct filename *filename,
goto out_free;

/*
- * When argv is empty, add an empty string ("") as argv[0] to
+ * When argv is empty, add bprm->filename as argv[0] to
* ensure confused userspace programs that start processing
* from argv[1] won't end up walking envp. See also
* bprm_stack_limits().
*/
if (bprm->argc == 0) {
- retval = copy_string_kernel("", bprm);
+ retval = copy_string_kernel(bprm->filename, bprm);
if (retval < 0)
goto out_free;
bprm->argc = 1;
--
2.17.1