If module name is empty, it is better to return directly at the beginning
of request_module() without doing the needless call_modprobe() operation.
(1) In the kernel space
Call trace:
request_module()
|
|
__request_module()
|
|
call_modprobe()
|
|
call_usermodehelper_exec() -- retval = sub_info->retval;
|
|
call_usermodehelper_exec_work()
|
|
call_usermodehelper_exec_sync() -- sub_info->retval = ret;
|
| --> call_usermodehelper_exec_async() --> do_execve()
|
kernel_wait4(pid, (int __user *)&ret, 0, NULL);
The exit status of child process is wrote to the address of variable
"ret" after call kernel_wait4(), its value is 256 if module name is
empty, then sub_info->retval is assigned to "ret" which is 256, the
function call_usermodehelper_exec() returns 256, call_modprobe() and
__request_module() also return 256.
(2)In the user space
when build and execute the following application, we can see the exit
status is 256.
$ ./system
exit status = 256
$ ./execl
exit status = 256
$ cat system.c
#include <stdio.h>
#include <stdlib.h>
int main()
{
int status = 0;
status = system("modprobe '' > /dev/null 2>&1");
printf("exit status = %d\n", status);
return status;
}
$ cat execl.c
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
pid_t pid, w;
int status;
pid = fork();
if (pid == -1) {
perror("fork");
exit(EXIT_FAILURE);
}
if (pid == 0) {
execl("/bin/sh", "sh", "-c",
"modprobe '' > /dev/null 2>&1", (char *) 0);
} else {
w = waitpid(pid, &status, 0);
if (w == -1) {
perror("waitpid");
exit(EXIT_FAILURE);
}
printf("exit status = %d\n", status);
exit(EXIT_SUCCESS);
}
return 0;
}
The exit status of child process is wrote to the address of variable
"status" after call waitpid() in the user space that corresponds with
kernel_wait4() in the kernel space.
Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
---
v4:
- update the commit message with application
v3:
- no changes
v2:
- update the commit message to explain the detailed reason
kernel/kmod.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/kmod.c b/kernel/kmod.c
index 3cd075c..5851444 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -28,6 +28,8 @@
#include <trace/events/module.h>
+#define MODULE_NOT_FOUND 256
+
/*
* Assuming:
*
@@ -144,6 +146,9 @@ int __request_module(bool wait, const char *fmt, ...)
if (ret >= MODULE_NAME_LEN)
return -ENAMETOOLONG;
+ if (strlen(module_name) == 0)
+ return MODULE_NOT_FOUND;
+
ret = security_kernel_module_request(module_name);
if (ret)
return ret;
--
2.1.0
