[PATCH v4 0/4] Fix some issues about kmod

[PATCH v4 0/4] Fix some issues about kmod

[Tiezhu Yang]

v4:
  - update the commit message with application of patch 3/4

v3:
  - use the quotes with correct format in the commit message of patch 4/4,
    sorry for that

v2:
  - update the commit message to explain the detailed reason of patch 3/4
  - add this cover letter

Tiezhu Yang (4):
  selftests: kmod: Use variable NAME in kmod_test_0001()
  kmod: Remove redundant "be an" in the comment
  kmod: Return directly if module name is empty in request_module()
  test_kmod: Avoid potential double free in trigger_config_run_type()

 kernel/kmod.c                        | 10 +++++++---
 lib/test_kmod.c                      |  2 +-
 tools/testing/selftests/kmod/kmod.sh |  4 ++--
 3 files changed, 10 insertions(+), 6 deletions(-)

-- 
2.1.0

[PATCH v4 1/4] selftests: kmod: Use variable NAME in kmod_test_0001()

[Tiezhu Yang]

Use the variable NAME instead of "\000" directly in kmod_test_0001().

Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---

v4:
  - no changes

v3:
  - no changes

v2:
  - just add the Acked-by tag

 tools/testing/selftests/kmod/kmod.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kmod/kmod.sh b/tools/testing/selftests/kmod/kmod.sh
index 3702dbc..da60c3b 100755
--- a/tools/testing/selftests/kmod/kmod.sh
+++ b/tools/testing/selftests/kmod/kmod.sh
@@ -341,7 +341,7 @@ kmod_test_0001_driver()
 
 	kmod_defaults_driver
 	config_num_threads 1
-	printf '\000' >"$DIR"/config_test_driver
+	printf $NAME >"$DIR"/config_test_driver
 	config_trigger ${FUNCNAME[0]}
 	config_expect_result ${FUNCNAME[0]} MODULE_NOT_FOUND
 }
@@ -352,7 +352,7 @@ kmod_test_0001_fs()
 
 	kmod_defaults_fs
 	config_num_threads 1
-	printf '\000' >"$DIR"/config_test_fs
+	printf $NAME >"$DIR"/config_test_fs
 	config_trigger ${FUNCNAME[0]}
 	config_expect_result ${FUNCNAME[0]} -EINVAL
 }
-- 
2.1.0

[PATCH v4 2/4] kmod: Remove redundant "be an" in the comment

[Tiezhu Yang]

There exists redundant "be an" in the comment, remove it.

Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---

v4:
  - no changes

v3:
  - no changes

v2:
  - just add the Acked-by tag

 kernel/kmod.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/kmod.c b/kernel/kmod.c
index 37c3c4b..3cd075c 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -36,9 +36,8 @@
  *
  * If you need less than 50 threads would mean we're dealing with systems
  * smaller than 3200 pages. This assumes you are capable of having ~13M memory,
- * and this would only be an be an upper limit, after which the OOM killer
- * would take effect. Systems like these are very unlikely if modules are
- * enabled.
+ * and this would only be an upper limit, after which the OOM killer would take
+ * effect. Systems like these are very unlikely if modules are enabled.
  */
 #define MAX_KMOD_CONCURRENT 50
 static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
-- 
2.1.0

[PATCH v4 3/4] kmod: Return directly if module name is empty in request_module()

[Tiezhu Yang]

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@loongson.cn>
---

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

[PATCH v4 4/4] test_kmod: Avoid potential double free in trigger_config_run_type()

[Tiezhu Yang]

Reset the member "test_fs" of the test configuration after a call
of the function "kfree_const" to a null pointer so that a double
memory release will not be performed.

Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---

v4:
  - no changes

v3:
  - use the quotes with correct format in the commit message,
    sorry for that

v2:
  - update the commit message suggested by Markus Elfring
  - add the Fixes tag

 lib/test_kmod.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/test_kmod.c b/lib/test_kmod.c
index e651c37..eab5277 100644
--- a/lib/test_kmod.c
+++ b/lib/test_kmod.c
@@ -745,7 +745,7 @@ static int trigger_config_run_type(struct kmod_test_device *test_dev,
 		break;
 	case TEST_KMOD_FS_TYPE:
 		kfree_const(config->test_fs);
-		config->test_driver = NULL;
+		config->test_fs = NULL;
 		copied = config_copy_test_fs(config, test_str,
 					     strlen(test_str));
 		break;
-- 
2.1.0

Re: [PATCH v4 3/4] kmod: Return directly if module name is empty in request_module()

[Luis Chamberlain]

On Tue, Apr 21, 2020 at 03:05:03PM +0800, Tiezhu Yang wrote:
> 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.

NACK, the issue is in umh, I'll send a fix.

  Luis

Re: [PATCH v4 0/4] Fix some issues about kmod

[Tiezhu Yang]

Hi,

Could you please apply the following three patches?

[v4,1/4] selftests: kmod: Use variable NAME in kmod_test_0001()
https://lore.kernel.org/patchwork/patch/1227980/

[v4,2/4] kmod: Remove redundant "be an" in the comment
https://lore.kernel.org/patchwork/patch/1227982/

[v4,4/4] test_kmod: Avoid potential double free in trigger_config_run_type()
https://lore.kernel.org/patchwork/patch/1227978/

Thanks,
Tiezhu Yang

Re: [PATCH v4 0/4] Fix some issues about kmod

[Luis Chamberlain]

On Mon, May 11, 2020 at 08:59:37PM +0800, Tiezhu Yang wrote:
> Hi,
> 
> Could you please apply the following three patches?
> 
> [v4,1/4] selftests: kmod: Use variable NAME in kmod_test_0001()
> https://lore.kernel.org/patchwork/patch/1227980/
> 
> [v4,2/4] kmod: Remove redundant "be an" in the comment
> https://lore.kernel.org/patchwork/patch/1227982/
> 
> [v4,4/4] test_kmod: Avoid potential double free in trigger_config_run_type()
> https://lore.kernel.org/patchwork/patch/1227978/

Andrew,

These 3 patches should be fine.

I am re-working a replacement proper fix for patch #3, that requires a
change to the umh. I'll try to iron this out today.

  Luis

Re: [PATCH v4 0/4] Fix some issues about kmod

[Luis Chamberlain]

On Mon, May 11, 2020 at 12:28 PM Luis Chamberlain <mcgrof@kernel.org> wrote:
>
> On Mon, May 11, 2020 at 08:59:37PM +0800, Tiezhu Yang wrote:
> > Hi,
> >
> > Could you please apply the following three patches?
> >
> > [v4,1/4] selftests: kmod: Use variable NAME in kmod_test_0001()
> > https://lore.kernel.org/patchwork/patch/1227980/
> >
> > [v4,2/4] kmod: Remove redundant "be an" in the comment
> > https://lore.kernel.org/patchwork/patch/1227982/
> >
> > [v4,4/4] test_kmod: Avoid potential double free in trigger_config_run_type()
> > https://lore.kernel.org/patchwork/patch/1227978/
>
> Andrew,
>
> These 3 patches should be fine.
>
> I am re-working a replacement proper fix for patch #3, that requires a
> change to the umh. I'll try to iron this out today.

I'll pick these up, and run tests now that I have a finalized solution
in place for the patch replacement I mentioned which was needed. Sorry
this took so long, but I am glad I took my time. I'll post soon after
I test the new fix.

  Luis