coredump_filter: enable to change the default filter

PATCH In review Hidehiro Kawai 4 participants 10 messages Dec 11, 2008 – Dec 26, 2008

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Documentation MM core Scheduler exec and binfmt

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Hidehiro Kawai

author

2008-12-11 07:00 UTC #0 lore raw

PATCH 1/1 coredump_filter: enable to change the default filter

This patch introduces new kernel parameter `coredump_filter'. Setting a value to this parameter causes the default bitmask of coredump_filter to be changed.

It is useful for users to change coredump_filter settings for the whole system at boot time. Without this parameter, users have to change coredump_filter settings for each /proc/<pid>/ in an initializing script.

Signed-off-by Hidehiro Kawai <[email protected]>

CC Roland McGrath <[email protected]>

CC Motohiro Kosaki <[email protected]>

---
 Documentation/kernel-parameters.txt |    5 +++++
 kernel/fork.c                       |   15 +++++++++++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

Documentation/kernel-parameters.txt +5 -0

Index: linux-2.6.28-rc8/Documentation/kernel-parameters.txt
===================================================================
@@ -547,6 +547,11 @@ and is between 256 and 4096 characters. 
 			not work reliably with all consoles, but is known
 			to work with serial and VGA consoles.
 
+	coredump_filter=
+			[KNL] Change the default value for
+			/proc/<pid>/coredump_filter.
+			See also Documentation/filesystems/proc.txt.
+
 	cpcihp_generic=	[HW,PCI] Generic port I/O CompactPCI driver
 			Format:
 			<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]

kernel/fork.c +13 -2

Index: linux-2.6.28-rc8/kernel/fork.c
===================================================================
@@ -397,6 +397,18 @@ __cacheline_aligned_in_smp DEFINE_SPINLO
 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
 
+static unsigned long default_dump_filter = MMF_DUMP_FILTER_DEFAULT;
+
+static int __init coredump_filter_setup(char *s)
+{
+	default_dump_filter =
+		(simple_strtoul(s, NULL, 0) << MMF_DUMP_FILTER_SHIFT) &
+		MMF_DUMP_FILTER_MASK;
+	return 1;
+}
+
+__setup("coredump_filter=", coredump_filter_setup);
+
 #include <linux/init_task.h>
 
 static struct mm_struct * mm_init(struct mm_struct * mm, struct task_struct *p)

@@ -405,8 +417,7 @@ static struct mm_struct * mm_init(struct
 	atomic_set(&mm->mm_count, 1);
 	init_rwsem(&mm->mmap_sem);
 	INIT_LIST_HEAD(&mm->mmlist);
-	mm->flags = (current->mm) ? current->mm->flags
-				  : MMF_DUMP_FILTER_DEFAULT;
+	mm->flags = (current->mm) ? current->mm->flags : default_dump_filter;
 	mm->core_state = NULL;
 	mm->nr_ptes = 0;
 	set_mm_counter(mm, file_rss, 0);

KOSAKI Motohiro

2008-12-11 06:47 UTC #1 lore raw

Quoted 8 lines

This patch introduces new kernel parameter `coredump_filter'. Setting a value to this parameter causes the default bitmask of coredump_filter to be changed.
It is useful for users to change coredump_filter settings for the whole system at boot time. Without this parameter, users have to change coredump_filter settings for each /proc/<pid>/ in an initializing script.

I think this patch only useful on following situation, right?

- Administrator can't change rc script.
- Administrator can change boot parameter.

When happen above situation?
or, you intent to init process debugging?

Andrew Morton

maintainer

2008-12-11 23:11 UTC #2 lore raw

Quoted 11 lines · On Thu, 11 Dec 2008 15:46:49 +0900 (JST) KOSAKI Motohiro…

Hi
Quoted 8 lines
This patch introduces new kernel parameter `coredump_filter'. Setting a value to this parameter causes the default bitmask of coredump_filter to be changed.
It is useful for users to change coredump_filter settings for the whole system at boot time. Without this parameter, users have to change coredump_filter settings for each /proc/<pid>/ in an initializing script.

Quoted 8 lines

I think this patch only useful on following situation, right?
- Administrator can't change rc script.
- Administrator can change boot parameter.
When happen above situation?
or, you intent to init process debugging?

Yes, this can be implemented in userspace by setting init's filter before init forks any other processes.

I can understand the practical problems with that form of implementation however :(

Or does the patch change other behaviour? Say, when mm_init() is called by a kernel thread (current->mm==NULL)? call_usermodehelper(), for example?

If so, then setting init's filter doesn't cover that case.

Roland McGrath

2008-12-11 23:22 UTC #3 lore raw

Quoted 5 lines

Or does the patch change other behaviour? Say, when mm_init() is called by a kernel thread (current->mm==NULL)? call_usermodehelper(), for example?
If so, then setting init's filter doesn't cover that case.

Hmm, probably for the kernel thread case mm_init should use task_active_pid_ns(current)->child_reaper->mm->flags.

Thanks,
Roland

Hidehiro Kawai

author

2008-12-19 10:05 UTC #4 lore raw

Hi,

Quoted 8 lines · Roland McGrath

Quoted 5 lines
Or does the patch change other behaviour? Say, when mm_init() is called by a kernel thread (current->mm==NULL)? call_usermodehelper(), for example?
If so, then setting init's filter doesn't cover that case.
Hmm, probably for the kernel thread case mm_init should use task_active_pid_ns(current)->child_reaper->mm->flags.

It makes sense. It also enables us to change coredump_filter for user mode helpers after the system was booted.

However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.

The reason why I suggested the boot parameter way is most users can change the default easily. Some users have difficulty to change init scripts for various reasons.

So I think the boot parameter way is simpler for both users and kernel developers.

Thanks,

Signature · 3 lines

Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center

Roland McGrath

2008-12-19 19:54 UTC #5 lore raw

Quoted 2 lines

It makes sense. It also enables us to change coredump_filter for user mode helpers after the system was booted.

Right.

Quoted 4 lines

However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.

I'd figured that private PID namespaces with their own init would want their own private settings for this default too.

Quoted 3 lines

The reason why I suggested the boot parameter way is most users can change the default easily. Some users have difficulty to change init scripts for various reasons.

I don't object to it deeply or anything.
I just pointed out that we do already have an alternative.

Thanks,
Roland

Hidehiro Kawai

author

2008-12-26 06:23 UTC #6 lore raw

Hi,

I'm sorry for late reply.

Quoted 7 lines · Roland McGrath

Quoted 4 lines
However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.
I'd figured that private PID namespaces with their own init would want their own private settings for this default too.

Probably it's true, but I'm not sure if having coredump_filter have two means is acceptable. init in a private PID namespace can die and dump a core file. So its coredump_filter has two means; default setting for the namespace and setting for itself.

Thanks,

Signature · 3 lines

Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center

KOSAKI Motohiro

2008-12-26 06:50 UTC #7 lore raw

Quoted 5 lines

Quoted 5 lines
Quoted 4 lines
However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.

Quoted 7 lines

Quoted 2 lines
I'd figured that private PID namespaces with their own init would want their own private settings for this default too.
Probably it's true, but I'm not sure if having coredump_filter have two means is acceptable. init in a private PID namespace can die and dump a core file. So its coredump_filter has two means; default setting for the namespace and setting for itself.

FWIW, I think private namespace should have private settings framework. I don't like to make special private settings code in this patch.

Yeah, defenitely we need to private settings for various reason, I agreed. but we also need consistent private settings rule and framework. otherwise, we will make various non consistent crap. maybe..

Hidehiro Kawai

author

2008-12-26 09:45 UTC #8 lore raw

Quoted 13 lines · KOSAKI Motohiro

Quoted 5 lines
Quoted 5 lines
Quoted 4 lines
However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.
Quoted 7 lines
Quoted 2 lines
I'd figured that private PID namespaces with their own init would want their own private settings for this default too.
Probably it's true, but I'm not sure if having coredump_filter have two means is acceptable. init in a private PID namespace can die and dump a core file. So its coredump_filter has two means; default setting for the namespace and setting for itself.

Quoted 6 lines

FWIW, I think private namespace should have private settings framework. I don't like to make special private settings code in this patch.
Yeah, defenitely we need to private settings for various reason, I agreed. but we also need consistent private settings rule and framework. otherwise, we will make various non consistent crap. maybe..

Anyway, as Andrew pointed out, current coredump filter doesn't care for user mode helpers. So we need some sort of changes in coredump filter so that users can change user mode helpers' settings; use child_reapers setting as default (Roland's suggestion) or use a boot parameter.

Thanks,

Signature · 3 lines

Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center

KOSAKI Motohiro

Acked-by

2008-12-26 11:46 UTC #9 lore raw

Quoted 20 lines

Quoted 13 lines
Quoted 5 lines
Quoted 5 lines
Quoted 4 lines
However, we would need a special care for PID namespace if we use init's coredump_filter as default. For a process with new PID namespace and new /proc, writing to /proc/1/coredump_filter doesn't mean changing default, although it's not a usual operation.
Quoted 7 lines
Quoted 2 lines
I'd figured that private PID namespaces with their own init would want their own private settings for this default too.
Probably it's true, but I'm not sure if having coredump_filter have two means is acceptable. init in a private PID namespace can die and dump a core file. So its coredump_filter has two means; default setting for the namespace and setting for itself.
Quoted 6 lines
FWIW, I think private namespace should have private settings framework. I don't like to make special private settings code in this patch.
Yeah, defenitely we need to private settings for various reason, I agreed. but we also need consistent private settings rule and framework. otherwise, we will make various non consistent crap. maybe..

Quoted 5 lines

Anyway, as Andrew pointed out, current coredump filter doesn't care for user mode helpers. So we need some sort of changes in coredump filter so that users can change user mode helpers' settings; use child_reapers setting as default (Roland's suggestion) or use a boot parameter.

hm, ok.
I agreed your patch is nice.

Acked-by KOSAKI Motohiro <[email protected]>