[RFC PATCH v2 0/2] lib, stackdepot: check stackdepot handle before accessing slabs

[RFC PATCH v2 0/2] lib, stackdepot: check stackdepot handle before accessing slabs

[Imran Khan]

Original cover letter
---------------------------------------
This RFC patch series addresses suggestion discussed in an earlier
RFC [1]. Since earlier RFC was about SLUB subsystem, and current
changes only involve stackdepot, I am submitting the patches in
a new thread.

The changes of this patch set are as follows:

PATCH-1: Checks validity of a stackdepot handle before proceeding
to access stackdepot slab/objects.

PATCH-2: Adds a helper in stackdepot, to allow users to print
stack entries just by specifying the stackdepot handle.   

[1] https://lore.kernel.org/lkml/2772cf56-4183-857f-d070-c54bceb5c8d9@suse.cz/
--------------------------------------

Changes in v2:
- remove WARN messages
- add declaration of stack_depot_print in stackdepot.h
- make current users, which use stack_depot_fetch + stack_trace_print 
  to print stack entries, use stack_depot_print

Imran Khan (2):
  lib, stackdepot: check stackdepot handle before accessing slabs.
  lib, stackdepot: Add helper to print stack entries.

 include/linux/stackdepot.h |  2 ++
 lib/stackdepot.c           | 20 ++++++++++++++++++++
 mm/kasan/report.c          | 15 +++------------
 mm/page_owner.c            | 13 ++++---------
 4 files changed, 29 insertions(+), 21 deletions(-)

-- 
2.30.2

[RFC PATCH v2 1/2] lib, stackdepot: check stackdepot handle before accessing slabs.

[Imran Khan]

stack_depot_save allocates slabs that will be used for storing
objects in future.If this slab allocation fails we may get to
a situation where space allocation for a new stack_record fails,
causing stack_depot_save to return 0 as handle.
If user of this handle ends up invoking stack_depot_fetch with
this handle value, current implementation of stack_depot_fetch
will end up using slab from wrong index.
To avoid this check handle value at the beginning.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
---
 lib/stackdepot.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 0a2e417f83cb..67439c082490 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -232,6 +232,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 	struct stack_record *stack;
 
 	*entries = NULL;
+	if (!handle)
+		return 0;
+
 	if (parts.slabindex > depot_index) {
 		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
 			parts.slabindex, depot_index, handle);
-- 
2.30.2

Re: [RFC PATCH v2 1/2] lib, stackdepot: check stackdepot handle before accessing slabs.

[Vlastimil Babka]

On 9/2/21 02:01, Imran Khan wrote:
> stack_depot_save allocates slabs that will be used for storing
> objects in future.If this slab allocation fails we may get to
> a situation where space allocation for a new stack_record fails,
> causing stack_depot_save to return 0 as handle.
> If user of this handle ends up invoking stack_depot_fetch with
> this handle value, current implementation of stack_depot_fetch
> will end up using slab from wrong index.
> To avoid this check handle value at the beginning.
> 
> Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  lib/stackdepot.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 0a2e417f83cb..67439c082490 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -232,6 +232,9 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
>  	struct stack_record *stack;
>  
>  	*entries = NULL;
> +	if (!handle)
> +		return 0;
> +
>  	if (parts.slabindex > depot_index) {
>  		WARN(1, "slab index %d out of bounds (%d) for stack id %08x\n",
>  			parts.slabindex, depot_index, handle);
> 

[RFC PATCH v2 2/2] lib, stackdepot: Add helper to print stack entries.

[Imran Khan]

To print a stack entries, users of stackdepot, first
use stack_depot_fetch to get a list of stack entries
and then use stack_trace_print to print this list.
Provide a helper in stackdepot to print stack entries
based on stackdepot handle.
Also change above mentioned users to use this helper.

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
---
 include/linux/stackdepot.h |  2 ++
 lib/stackdepot.c           | 17 +++++++++++++++++
 mm/kasan/report.c          | 15 +++------------
 mm/page_owner.c            | 13 ++++---------
 4 files changed, 26 insertions(+), 21 deletions(-)

diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index 6bb4bc1a5f54..d77a30543dd4 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -19,6 +19,8 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries);
 
+void stack_depot_print(depot_stack_handle_t stack);
+
 unsigned int filter_irq_stacks(unsigned long *entries, unsigned int nr_entries);
 
 #ifdef CONFIG_STACKDEPOT
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 67439c082490..873aeb152f52 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -214,6 +214,23 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
 	return NULL;
 }
 
+/**
+ * stack_depot_print - print stack entries from a depot
+ *
+ * @handle:		Stack depot handle which was returned from
+ *			stack_depot_save().
+ *
+ */
+void stack_depot_print(depot_stack_handle_t stack)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(stack, &entries);
+	stack_trace_print(entries, nr_entries, 0);
+}
+EXPORT_SYMBOL_GPL(stack_depot_print);
+
 /**
  * stack_depot_fetch - Fetch stack entries from a depot
  *
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 884a950c7026..3239fd8f8747 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -132,20 +132,11 @@ static void end_report(unsigned long *flags, unsigned long addr)
 	kasan_enable_current();
 }
 
-static void print_stack(depot_stack_handle_t stack)
-{
-	unsigned long *entries;
-	unsigned int nr_entries;
-
-	nr_entries = stack_depot_fetch(stack, &entries);
-	stack_trace_print(entries, nr_entries, 0);
-}
-
 static void print_track(struct kasan_track *track, const char *prefix)
 {
 	pr_err("%s by task %u:\n", prefix, track->pid);
 	if (track->stack) {
-		print_stack(track->stack);
+		stack_depot_print(track->stack);
 	} else {
 		pr_err("(stack is not available)\n");
 	}
@@ -214,12 +205,12 @@ static void describe_object_stacks(struct kmem_cache *cache, void *object,
 		return;
 	if (alloc_meta->aux_stack[0]) {
 		pr_err("Last potentially related work creation:\n");
-		print_stack(alloc_meta->aux_stack[0]);
+		stack_depot_print(alloc_meta->aux_stack[0]);
 		pr_err("\n");
 	}
 	if (alloc_meta->aux_stack[1]) {
 		pr_err("Second to last potentially related work creation:\n");
-		print_stack(alloc_meta->aux_stack[1]);
+		stack_depot_print(alloc_meta->aux_stack[1]);
 		pr_err("\n");
 	}
 #endif
diff --git a/mm/page_owner.c b/mm/page_owner.c
index d24ed221357c..7918770c2b2b 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -394,8 +394,6 @@ void __dump_page_owner(const struct page *page)
 	struct page_ext *page_ext = lookup_page_ext(page);
 	struct page_owner *page_owner;
 	depot_stack_handle_t handle;
-	unsigned long *entries;
-	unsigned int nr_entries;
 	gfp_t gfp_mask;
 	int mt;
 
@@ -423,20 +421,17 @@ void __dump_page_owner(const struct page *page)
 		 page_owner->pid, page_owner->ts_nsec, page_owner->free_ts_nsec);
 
 	handle = READ_ONCE(page_owner->handle);
-	if (!handle) {
+	if (!handle)
 		pr_alert("page_owner allocation stack trace missing\n");
-	} else {
-		nr_entries = stack_depot_fetch(handle, &entries);
-		stack_trace_print(entries, nr_entries, 0);
-	}
+	else
+		stack_depot_print(handle);
 
 	handle = READ_ONCE(page_owner->free_handle);
 	if (!handle) {
 		pr_alert("page_owner free stack trace missing\n");
 	} else {
-		nr_entries = stack_depot_fetch(handle, &entries);
 		pr_alert("page last free stack trace:\n");
-		stack_trace_print(entries, nr_entries, 0);
+		stack_depot_print(handle);
 	}
 
 	if (page_owner->last_migrate_reason != -1)
-- 
2.30.2

Re: [RFC PATCH v2 2/2] lib, stackdepot: Add helper to print stack entries.

[Vlastimil Babka]

On 9/2/21 02:01, Imran Khan wrote:
> To print a stack entries, users of stackdepot, first
> use stack_depot_fetch to get a list of stack entries
> and then use stack_trace_print to print this list.
> Provide a helper in stackdepot to print stack entries
> based on stackdepot handle.
> Also change above mentioned users to use this helper.
> 
> Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Re: [RFC PATCH v2 2/2] lib, stackdepot: Add helper to print stack entries.

[Alexander Potapenko]

On Thu, Sep 2, 2021 at 9:55 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 9/2/21 02:01, Imran Khan wrote:
> > To print a stack entries, users of stackdepot, first
> > use stack_depot_fetch to get a list of stack entries
> > and then use stack_trace_print to print this list.
> > Provide a helper in stackdepot to print stack entries
> > based on stackdepot handle.
> > Also change above mentioned users to use this helper.
> >
> > Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
> > Suggested-by: Vlastimil Babka <vbabka@suse.cz>
>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Reviewed-by: Alexander Potapenko <glider@google.com>

-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

Re: [RFC PATCH v2 2/2] lib, stackdepot: Add helper to print stack entries.

[Vlastimil Babka]

On 9/2/21 02:01, Imran Khan wrote:
> To print a stack entries, users of stackdepot, first
> use stack_depot_fetch to get a list of stack entries
> and then use stack_trace_print to print this list.
> Provide a helper in stackdepot to print stack entries
> based on stackdepot handle.
> Also change above mentioned users to use this helper.
> 
> Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
> Suggested-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  include/linux/stackdepot.h |  2 ++
>  lib/stackdepot.c           | 17 +++++++++++++++++
>  mm/kasan/report.c          | 15 +++------------
>  mm/page_owner.c            | 13 ++++---------
>  4 files changed, 26 insertions(+), 21 deletions(-)
> 
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index 6bb4bc1a5f54..d77a30543dd4 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -19,6 +19,8 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
>  unsigned int stack_depot_fetch(depot_stack_handle_t handle,
>  			       unsigned long **entries);
>  
> +void stack_depot_print(depot_stack_handle_t stack);
> +
>  unsigned int filter_irq_stacks(unsigned long *entries, unsigned int nr_entries);
>  
>  #ifdef CONFIG_STACKDEPOT
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 67439c082490..873aeb152f52 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -214,6 +214,23 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
>  	return NULL;
>  }
>  
> +/**
> + * stack_depot_print - print stack entries from a depot
> + *
> + * @handle:		Stack depot handle which was returned from
> + *			stack_depot_save().
> + *
> + */
> +void stack_depot_print(depot_stack_handle_t stack)
> +{
> +	unsigned long *entries;
> +	unsigned int nr_entries;
> +
> +	nr_entries = stack_depot_fetch(stack, &entries);

Maybe this should also skip stack_trace_print when nr_entries is 0, to avoid
the warning. While the callers added by this patch check handle != 0, future
ones might not.

Re: [RFC PATCH v2 2/2] lib, stackdepot: Add helper to print stack entries.

[imran.f.khan]

On 14/9/21 7:01 pm, Vlastimil Babka wrote:
> On 9/2/21 02:01, Imran Khan wrote:
>> To print a stack entries, users of stackdepot, first
>> use stack_depot_fetch to get a list of stack entries
>> and then use stack_trace_print to print this list.
>> Provide a helper in stackdepot to print stack entries
>> based on stackdepot handle.
>> Also change above mentioned users to use this helper.
>>

[...]
>>   
>> +/**
>> + * stack_depot_print - print stack entries from a depot
>> + *
>> + * @handle:		Stack depot handle which was returned from
>> + *			stack_depot_save().
>> + *
>> + */
>> +void stack_depot_print(depot_stack_handle_t stack)
>> +{
>> +	unsigned long *entries;
>> +	unsigned int nr_entries;
>> +
>> +	nr_entries = stack_depot_fetch(stack, &entries);
> 
> Maybe this should also skip stack_trace_print when nr_entries is 0, to avoid
> the warning. While the callers added by this patch check handle != 0, future
> ones might not.
> 
Agree. I have incorporated this suggestion in latest version [1]

[1] 
https://lore.kernel.org/lkml/20210915014806.3206938-1-imran.f.khan@oracle.com/

Thanks
   -- Imran