[PATCH 1/1] coredump: use task comm instead of (unknown)

[PATCH 1/1] coredump: use task comm instead of (unknown)

[Jiri Slaby]

If we don't know the file corresponding to the binary (i.e. exe_file
is unknown), use "task->comm (path unknown)" instead of simple
"(unknown)" as suggested by ak.

The fallback is the same as %e except it will append "(path unknown)".

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andi Kleen <andi@firstfloor.org>
---
 fs/exec.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 5ee7562..0a4d281 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1555,7 +1555,7 @@ static int cn_print_exe_file(struct core_name *cn)
 
 	exe_file = get_mm_exe_file(current->mm);
 	if (!exe_file)
-		return cn_printf(cn, "(unknown)");
+		return cn_printf(cn, "%s (path unknown)", current->comm);
 
 	pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
 	if (!pathbuf) {
-- 
1.7.4.2


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Re: [PATCH 1/1] coredump: use task comm instead of (unknown)

[Andrew Morton]

On Wed,  4 May 2011 09:32:34 +0200
Jiri Slaby <jslaby@suse.cz> wrote:

> If we don't know the file corresponding to the binary (i.e. exe_file
> is unknown), use "task->comm (path unknown)" instead of simple
> "(unknown)" as suggested by ak.
> 
> The fallback is the same as %e except it will append "(path unknown)".
> 
> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Andi Kleen <andi@firstfloor.org>
> ---
>  fs/exec.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index 5ee7562..0a4d281 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1555,7 +1555,7 @@ static int cn_print_exe_file(struct core_name *cn)
>  
>  	exe_file = get_mm_exe_file(current->mm);
>  	if (!exe_file)
> -		return cn_printf(cn, "(unknown)");
> +		return cn_printf(cn, "%s (path unknown)", current->comm);
>  
>  	pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
>  	if (!pathbuf) {

Direct access to current->comm is racy since we added
prctl(PR_SET_NAME).

Hopefully John Stultz will soon be presenting us with a %p modifier for
displaying task_struct.comm.

But we should get this settled pretty promptly as this is a form of
userspace-visible API.  Use get_task_comm() for now.

Also, there's nothing which prevents userspace from rewriting
task->comm to something which contains slashes (this seems bad).  If
that is done, your patch will do Bad Things - it should be modified to
use cn_print_exe_file()'s slash-overwriting codepath.

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Re: [PATCH 1/1] coredump: use task comm instead of (unknown)

[Jiri Slaby]

Ccing Oleg.

On 05/06/2011 12:06 AM, Andrew Morton wrote:
> On Wed,  4 May 2011 09:32:34 +0200
> Jiri Slaby <jslaby@suse.cz> wrote:
> 
>> If we don't know the file corresponding to the binary (i.e. exe_file
>> is unknown), use "task->comm (path unknown)" instead of simple
>> "(unknown)" as suggested by ak.
>>
>> The fallback is the same as %e except it will append "(path unknown)".
>>
>> Signed-off-by: Jiri Slaby <jslaby@suse.cz>
>> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>> Cc: Andi Kleen <andi@firstfloor.org>
>> ---
>>  fs/exec.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> index 5ee7562..0a4d281 100644
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -1555,7 +1555,7 @@ static int cn_print_exe_file(struct core_name *cn)
>>  
>>  	exe_file = get_mm_exe_file(current->mm);
>>  	if (!exe_file)
>> -		return cn_printf(cn, "(unknown)");
>> +		return cn_printf(cn, "%s (path unknown)", current->comm);
>>  
>>  	pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
>>  	if (!pathbuf) {
> 
> Direct access to current->comm is racy since we added
> prctl(PR_SET_NAME).
> 
> Hopefully John Stultz will soon be presenting us with a %p modifier for
> displaying task_struct.comm.

Then just make sure, you won't nest alloc_lock (task_lock) into siglock.

> But we should get this settled pretty promptly as this is a form of
> userspace-visible API.  Use get_task_comm() for now.

I thought about using get_task_comm, but was not sure, if it is safe to
task_lock() at that place. Note that this is copied from %e.

> Also, there's nothing which prevents userspace from rewriting
> task->comm to something which contains slashes (this seems bad).  If
> that is done, your patch will do Bad Things - it should be modified to
> use cn_print_exe_file()'s slash-overwriting codepath.

%E (cn_print_exe_file) does exactly what %e (format_corename) does. So
if this is really broken in the two ways, we should fix both the old %e
and the new %E.

I'm not sure whether at this point when the task is being killed and
dumped, it can still change comm?

For the slashes, I agree. That should be fixed in both cases.

thanks,
-- 
js
suse labs

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