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[PATCH v2] rcu: Fix buffer overlow in print_cpu_stall_info()

Nikita Kiryushin posted 1 patch 1 year, 10 months ago
There is a newer version of this series
kernel/rcu/tree_stall.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
[PATCH v2] rcu: Fix buffer overlow in print_cpu_stall_info()
Posted by Nikita Kiryushin 1 year, 10 months ago 
rcuc info output in print_cpu_stall_info() contains
possible buffer overflow in the case of huge jiffies
difference. The situation seems improbable, but, buffer
overflow, still.

Also, unsigned jiffies difference printed as (signed)
%ld. This is intentional for debugging purposes, but
it is not obvious from the code.

Change sprintf to snprintf and add clarifying comment
about intention of %ld format.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 245a62982502 ("rcu: Dump rcuc kthread status for CPUs not reporting quiescent state")
Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
---
v2: Remove signed to unsigned print format change as
Paul E. McKenney <paulmck@kernel.org> suggested, add format
intention clarification comment
 kernel/rcu/tree_stall.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5d666428546b..b972fe9f07a6 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -504,7 +504,8 @@ static void print_cpu_stall_info(int cpu)
 			rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
 	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
 	if (rcuc_starved)
-		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
+		/* %ld is intentional, for easier bug detection */
+		snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j);
 	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
 	       cpu,
 	       "O."[!!cpu_online(cpu)],
-- 
2.34.1
Re: [PATCH v2] rcu: Fix buffer overlow in print_cpu_stall_info()
Posted by Steven Rostedt 1 year, 10 months ago 
On Mon,  1 Apr 2024 21:54:54 +0300
Nikita Kiryushin <kiryushin@ancud.ru> wrote:

> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -504,7 +504,8 @@ static void print_cpu_stall_info(int cpu)
>  			rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
>  	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
>  	if (rcuc_starved)
> -		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
> +		/* %ld is intentional, for easier bug detection */

The above still has assumptions of what is going on for the reviewer.
I would suggest something a bit more obvious like:

		/* Print signed value, as negative means it is likely a bug */


> +		snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j);
>  	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",

-- Steve
[PATCH v3] rcu: Fix buffer overlow in print_cpu_stall_info()
Posted by Nikita Kiryushin 1 year, 10 months ago 
rcuc info output in print_cpu_stall_info() contains
posiible buffer overflow in the case of huge jiffies
difference. The situation seems improbable, but, buffer
overflow, still.

Also, unsigned jiffies difference printed as (signed)
%ld. This is intentional for debugging purposes, but
it is not obvious from the code.

Change sprintf to snprintf and add clarifying comment
about intention of %ld format.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 245a62982502 ("rcu: Dump rcuc kthread status for CPUs not reporting quiescent state")
Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
---
v3: Change intention comment wording as
Steven Rostedt <rostedt@goodmis.org> suggested
v2: Remove signed to unsigned print format change as
Paul E. McKenney <paulmck@kernel.org> suggested, add format
intention clarification comment
 kernel/rcu/tree_stall.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5d666428546b..320440b8384e 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -504,7 +504,8 @@ static void print_cpu_stall_info(int cpu)
 			rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
 	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
 	if (rcuc_starved)
-		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
+		/* Print signed value, as negative means it is likely a bug */
+		snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j);
 	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
 	       cpu,
 	       "O."[!!cpu_online(cpu)],
-- 
2.34.1
Re: [PATCH v3] rcu: Fix buffer overlow in print_cpu_stall_info()
Posted by Steven Rostedt 1 year, 10 months ago 
On Mon,  1 Apr 2024 22:43:15 +0300
Nikita Kiryushin <kiryushin@ancud.ru> wrote:

> rcuc info output in print_cpu_stall_info() contains
> posiible buffer overflow in the case of huge jiffies
> difference. The situation seems improbable, but, buffer
> overflow, still.
> 
> Also, unsigned jiffies difference printed as (signed)
> %ld. This is intentional for debugging purposes, but
> it is not obvious from the code.
> 
> Change sprintf to snprintf and add clarifying comment
> about intention of %ld format.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: 245a62982502 ("rcu: Dump rcuc kthread status for CPUs not reporting quiescent state")
> Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
> ---
> v3: Change intention comment wording as
> Steven Rostedt <rostedt@goodmis.org> suggested
> v2: Remove signed to unsigned print format change as
> Paul E. McKenney <paulmck@kernel.org> suggested, add format
> intention clarification comment
>  kernel/rcu/tree_stall.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 5d666428546b..320440b8384e 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -504,7 +504,8 @@ static void print_cpu_stall_info(int cpu)
>  			rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
>  	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
>  	if (rcuc_starved)
> -		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
> +		/* Print signed value, as negative means it is likely a bug */
> +		snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j);
>  	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
>  	       cpu,
>  	       "O."[!!cpu_online(cpu)],


Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve
Re: [PATCH v3] rcu: Fix buffer overlow in print_cpu_stall_info()
Posted by Paul E. McKenney 1 year, 10 months ago 
On Mon, Apr 01, 2024 at 04:03:12PM -0400, Steven Rostedt wrote:
> On Mon,  1 Apr 2024 22:43:15 +0300
> Nikita Kiryushin <kiryushin@ancud.ru> wrote:
> 
> > rcuc info output in print_cpu_stall_info() contains
> > posiible buffer overflow in the case of huge jiffies
> > difference. The situation seems improbable, but, buffer
> > overflow, still.
> > 
> > Also, unsigned jiffies difference printed as (signed)
> > %ld. This is intentional for debugging purposes, but
> > it is not obvious from the code.
> > 
> > Change sprintf to snprintf and add clarifying comment
> > about intention of %ld format.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Fixes: 245a62982502 ("rcu: Dump rcuc kthread status for CPUs not reporting quiescent state")
> > Signed-off-by: Nikita Kiryushin <kiryushin@ancud.ru>
> > ---
> > v3: Change intention comment wording as
> > Steven Rostedt <rostedt@goodmis.org> suggested
> > v2: Remove signed to unsigned print format change as
> > Paul E. McKenney <paulmck@kernel.org> suggested, add format
> > intention clarification comment
> >  kernel/rcu/tree_stall.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> > index 5d666428546b..320440b8384e 100644
> > --- a/kernel/rcu/tree_stall.h
> > +++ b/kernel/rcu/tree_stall.h
> > @@ -504,7 +504,8 @@ static void print_cpu_stall_info(int cpu)
> >  			rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
> >  	rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j);
> >  	if (rcuc_starved)
> > -		sprintf(buf, " rcuc=%ld jiffies(starved)", j);
> > +		/* Print signed value, as negative means it is likely a bug */
> > +		snprintf(buf, sizeof(buf), " rcuc=%ld jiffies(starved)", j);
> >  	pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n",
> >  	       cpu,
> >  	       "O."[!!cpu_online(cpu)],
> 
> 
> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Queued for v6.10, thank you both!

							Thanx, Paul

Patchew 2.1-devel-b67e4c2

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