If module name is empty, it is better to return directly at the beginning
of request_module() without doing the needless call_modprobe() operation.
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);
sub_info->retval is 256 after call kernel_wait4(), the function
call_usermodehelper_exec() returns sub_info->retval which is 256,
then call_modprobe() and __request_module() returns 256.
Signed-off-by: Tiezhu Yang <[email protected]>
---
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
On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote:
> If module name is empty, it is better to return directly at the beginning
> of request_module() without doing the needless call_modprobe() operation.
>
> 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);
>
> sub_info->retval is 256 after call kernel_wait4(), the function
> call_usermodehelper_exec() returns sub_info->retval which is 256,
> then call_modprobe() and __request_module() returns 256.
>
> Signed-off-by: Tiezhu Yang <[email protected]>
Thanks for looking into this. I still cannot find where
userspace it returns 256. Can you? If I run modprobe without
an argument I see 1 returned.
At least kmod [0] has a series of cmd helper structs, the one for modprobe
seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which
can be converted to 255. It can also return EXIT_FAILURE or EXIT_SUCCESS
and /usr/include/stdlib.h defines these as 1 and 0 respectively.
https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/
Luis
On 04/21/2020 02:19 AM, Luis Chamberlain wrote:
> On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote:
>> If module name is empty, it is better to return directly at the beginning
>> of request_module() without doing the needless call_modprobe() operation.
>>
>> 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);
>>
>> sub_info->retval is 256 after call kernel_wait4(), the function
>> call_usermodehelper_exec() returns sub_info->retval which is 256,
>> then call_modprobe() and __request_module() returns 256.
>>
>> Signed-off-by: Tiezhu Yang <[email protected]>
> Thanks for looking into this. I still cannot find where
> userspace it returns 256. Can you? If I run modprobe without
> an argument I see 1 returned.
>
> At least kmod [0] has a series of cmd helper structs, the one for modprobe
> seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which
> can be converted to 255. It can also return EXIT_FAILURE or EXIT_SUCCESS
> and /usr/include/stdlib.h defines these as 1 and 0 respectively.
>
> https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/
>
> Luis
Here is my understanding:
When build and execute the following application, we can see the exit
status is 256.
$ ./system
modprobe: FATAL: Module not found in directory
/lib/modules/4.18.0-147.5.1.el8_1.x86_64
exit status = 256
$ ./execl
modprobe: FATAL: Module not found in directory
/lib/modules/4.18.0-147.5.1.el8_1.x86_64
exit status = 256
$ cat system.c
#include <stdio.h>
#include <stdlib.h>
int main()
{
int status = 0;
status = system("modprobe ''");
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 aaa", (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 correspond with
kernel_wait4() [1]
in the kernel space.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/exit.c#n1576
+++ Tiezhu Yang [21/04/20 11:07 +0800]:
>On 04/21/2020 02:19 AM, Luis Chamberlain wrote:
>>On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote:
>>>If module name is empty, it is better to return directly at the beginning
>>>of request_module() without doing the needless call_modprobe() operation.
>>>
>>>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);
>>>
>>>sub_info->retval is 256 after call kernel_wait4(), the function
>>>call_usermodehelper_exec() returns sub_info->retval which is 256,
>>>then call_modprobe() and __request_module() returns 256.
>>>
>>>Signed-off-by: Tiezhu Yang <[email protected]>
>>Thanks for looking into this. I still cannot find where
>>userspace it returns 256. Can you? If I run modprobe without
>>an argument I see 1 returned.
>>
>>At least kmod [0] has a series of cmd helper structs, the one for modprobe
>>seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which
>>can be converted to 255. It can also return EXIT_FAILURE or EXIT_SUCCESS
>>and /usr/include/stdlib.h defines these as 1 and 0 respectively.
I'm also seeing modprobe return 1 as exit status when I run it without
arguments. I don't think the 256 value is coming from modprobe though,
see below -
>>https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/
>>
>> Luis
>
>Here is my understanding:
>
>When build and execute the following application, we can see the exit
>status is 256.
>
>$ ./system
>modprobe: FATAL: Module not found in directory
>/lib/modules/4.18.0-147.5.1.el8_1.x86_64
>exit status = 256
>
>$ ./execl
>modprobe: FATAL: Module not found in directory
>/lib/modules/4.18.0-147.5.1.el8_1.x86_64
>exit status = 256
I am going to guess this has something to do with how system() and
waitpid() (and the wait family of syscalls in general) encode the exit
status in their return values. According to their man pages, you need
to use the appropriate WIF* macros to get the actual exit code of the
child process.
From system(3):
the return value is a "wait status" that can be examined using the
macros described in waitpid(2). (i.e., WIFEXITED(),
WEXITSTATUS(), and so on)
From waitpid(2):
If wstatus is not NULL, wait() and waitpid() store status
information in the int to which it points. This integer can be
inspected with the following macros (which take the integer
itself as an argument, not a pointer to it, as is done in wait()
and waitpid()!):
WEXITSTATUS(wstatus)
returns the exit status of the child. This consists of
the least significant 8 bits of the status argument that
the child specified in a call to exit(3) or _exit(2) or
as the argument for a return statement in main(). This
macro should be employed only if WIFEXITED returned
true.
In your test code, you are reading &status directly. To obtain the
exit status, you need to use WEXITSTATUS(status), or right shift the
value by 8 bits. That gives you 1, which was the original exit code
given by modprobe. That's why you see an exit code of 1 when running
modprobe directly and you see 256 when using system() and waitpid()
and don't use the WIF* macros.
As for why __request_module() returns 256, I am guessing this would
come from kernel_wait4(), but I did not dive into the call path to
verify this yet.
Jessica
On Tue, Apr 21, 2020 at 04:49:32PM +0200, Jessica Yu wrote:
> As for why __request_module() returns 256, I am guessing this would
> come from kernel_wait4(), but I did not dive into the call path to
> verify this yet.
I got it. I'll send a fix.
Luis
On 04/21/2020 10:49 PM, Jessica Yu wrote:
> +++ Tiezhu Yang [21/04/20 11:07 +0800]:
>> On 04/21/2020 02:19 AM, Luis Chamberlain wrote:
>>> On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote:
>>>> If module name is empty, it is better to return directly at the
>>>> beginning
>>>> of request_module() without doing the needless call_modprobe()
>>>> operation.
>>>>
>>>> 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);
>>>>
>>>> sub_info->retval is 256 after call kernel_wait4(), the function
>>>> call_usermodehelper_exec() returns sub_info->retval which is 256,
>>>> then call_modprobe() and __request_module() returns 256.
>>>>
>>>> Signed-off-by: Tiezhu Yang <[email protected]>
>>> Thanks for looking into this. I still cannot find where
>>> userspace it returns 256. Can you? If I run modprobe without
>>> an argument I see 1 returned.
>>>
>>> At least kmod [0] has a series of cmd helper structs, the one for
>>> modprobe
>>> seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which
>>> can be converted to 255. It can also return EXIT_FAILURE or
>>> EXIT_SUCCESS
>>> and /usr/include/stdlib.h defines these as 1 and 0 respectively.
>
> I'm also seeing modprobe return 1 as exit status when I run it without
> arguments. I don't think the 256 value is coming from modprobe though,
> see below -
>
>>> https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/
>>>
>>> Luis
>>
>> Here is my understanding:
>>
>> When build and execute the following application, we can see the exit
>> status is 256.
>>
>> $ ./system
>> modprobe: FATAL: Module not found in directory
>> /lib/modules/4.18.0-147.5.1.el8_1.x86_64
>> exit status = 256
>>
>> $ ./execl
>> modprobe: FATAL: Module not found in directory
>> /lib/modules/4.18.0-147.5.1.el8_1.x86_64
>> exit status = 256
>
> I am going to guess this has something to do with how system() and
> waitpid() (and the wait family of syscalls in general) encode the exit
> status in their return values. According to their man pages, you need
> to use the appropriate WIF* macros to get the actual exit code of the
> child process.
>
> From system(3):
>
> the return value is a "wait status" that can be examined using the
> macros described in waitpid(2). (i.e., WIFEXITED(),
> WEXITSTATUS(), and so on)
>
> From waitpid(2):
>
> If wstatus is not NULL, wait() and waitpid() store status
> information in the int to which it points. This integer can be
> inspected with the following macros (which take the integer
> itself as an argument, not a pointer to it, as is done in wait()
> and waitpid()!):
>
> WEXITSTATUS(wstatus)
> returns the exit status of the child. This consists of
> the least significant 8 bits of the status argument that
> the child specified in a call to exit(3) or _exit(2) or
> as the argument for a return statement in main(). This
> macro should be employed only if WIFEXITED returned
> true.
>
> In your test code, you are reading &status directly. To obtain the
> exit status, you need to use WEXITSTATUS(status), or right shift the
> value by 8 bits. That gives you 1, which was the original exit code
> given by modprobe. That's why you see an exit code of 1 when running
> modprobe directly and you see 256 when using system() and waitpid()
> and don't use the WIF* macros.
>
> As for why __request_module() returns 256, I am guessing this would
> come from kernel_wait4(), but I did not dive into the call path to
> verify this yet.
+Cc Al Viro <[email protected]>
Hi Al,
When module name is empty, __request_module() returns 256.
What do you think about this case and patch?
Thank you very much for your attention.
patch v3:
https://lore.kernel.org/patchwork/patch/1227274/
patch v4 (update the commit message):
https://lore.kernel.org/patchwork/patch/1227981/
>
> Jessica
On Wed, Apr 22, 2020 at 04:55:34PM +0800, Tiezhu Yang wrote:
> On 04/21/2020 10:49 PM, Jessica Yu wrote:
> > +++ Tiezhu Yang [21/04/20 11:07 +0800]:
> > > On 04/21/2020 02:19 AM, Luis Chamberlain wrote:
> > > > On Mon, Apr 20, 2020 at 08:33:54PM +0800, Tiezhu Yang wrote:
> > > > > If module name is empty, it is better to return directly at
> > > > > the beginning
> > > > > of request_module() without doing the needless
> > > > > call_modprobe() operation.
> > > > >
> > > > > 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);
> > > > >
> > > > > sub_info->retval is 256 after call kernel_wait4(), the function
> > > > > call_usermodehelper_exec() returns sub_info->retval which is 256,
> > > > > then call_modprobe() and __request_module() returns 256.
> > > > >
> > > > > Signed-off-by: Tiezhu Yang <[email protected]>
> > > > Thanks for looking into this. I still cannot find where
> > > > userspace it returns 256. Can you? If I run modprobe without
> > > > an argument I see 1 returned.
> > > >
> > > > At least kmod [0] has a series of cmd helper structs, the one
> > > > for modprobe
> > > > seems to be kmod_cmd_compat_modprobe, and I can see -1 returned which
> > > > can be converted to 255. It can also return EXIT_FAILURE or
> > > > EXIT_SUCCESS
> > > > and /usr/include/stdlib.h defines these as 1 and 0 respectively.
> >
> > I'm also seeing modprobe return 1 as exit status when I run it without
> > arguments. I don't think the 256 value is coming from modprobe though,
> > see below -
> >
> > > > https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/
> > > >
> > > > Luis
> > >
> > > Here is my understanding:
> > >
> > > When build and execute the following application, we can see the
> > > exit status is 256.
> > >
> > > $ ./system
> > > modprobe: FATAL: Module not found in directory
> > > /lib/modules/4.18.0-147.5.1.el8_1.x86_64
> > > exit status = 256
> > >
> > > $ ./execl
> > > modprobe: FATAL: Module not found in directory
> > > /lib/modules/4.18.0-147.5.1.el8_1.x86_64
> > > exit status = 256
> >
> > I am going to guess this has something to do with how system() and
> > waitpid() (and the wait family of syscalls in general) encode the exit
> > status in their return values. According to their man pages, you need
> > to use the appropriate WIF* macros to get the actual exit code of the
> > child process.
> >
> > From system(3):
> >
> > the return value is a "wait status" that can be examined using the
> > macros described in waitpid(2). (i.e., WIFEXITED(),
> > WEXITSTATUS(), and so on)
> >
> > From waitpid(2):
> >
> > If wstatus is not NULL, wait() and waitpid() store status
> > information in the int to which it points. This integer can be
> > inspected with the following macros (which take the integer
> > itself as an argument, not a pointer to it, as is done in wait()
> > and waitpid()!):
> >
> > WEXITSTATUS(wstatus)
> > returns the exit status of the child. This consists of
> > the least significant 8 bits of the status argument that
> > the child specified in a call to exit(3) or _exit(2) or
> > as the argument for a return statement in main(). This
> > macro should be employed only if WIFEXITED returned
> > true.
> >
> > In your test code, you are reading &status directly. To obtain the
> > exit status, you need to use WEXITSTATUS(status), or right shift the
> > value by 8 bits. That gives you 1, which was the original exit code
> > given by modprobe. That's why you see an exit code of 1 when running
> > modprobe directly and you see 256 when using system() and waitpid()
> > and don't use the WIF* macros.
> >
> > As for why __request_module() returns 256, I am guessing this would
> > come from kernel_wait4(), but I did not dive into the call path to
> > verify this yet.
>
> +Cc Al Viro <[email protected]>
>
> Hi Al,
>
> When module name is empty, __request_module() returns 256.
> What do you think about this case and patch?
> Thank you very much for your attention.
Its because of an old issue umh.c, I'll send a patch.
Luis