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 (which can be a bad format, if the values
are huge).
Change sprintf to snprintf and change %ld to %lu in 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 <[email protected]>
---
kernel/rcu/tree_stall.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 5d666428546b..d4542c6e7c60 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -504,7 +504,7 @@ 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);
+ snprintf(buf, sizeof(buf), " rcuc=%lu 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
On Thu, Mar 28, 2024 at 09:19:14PM +0300, Nikita Kiryushin 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 (which can be a bad format, if the values
> are huge).
>
> Change sprintf to snprintf and change %ld to %lu in format.
Good catch!!!
However, the signed output is intentional. The idea is that if the
timekeeping code is confused enough to run the jiffies counter backwards,
we see a small negative number rather than a huge positive number.
For example, -132 is immediately obvious, while the 64-bit unsigned
equivalent of 18446744073709551484 might not be.
would you like to resend keeping the buffer-overflow fix but leaving
out the signed-to-unsigned conversion?
Thanx, Paul
> 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 <[email protected]>
> ---
> kernel/rcu/tree_stall.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 5d666428546b..d4542c6e7c60 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -504,7 +504,7 @@ 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);
> + snprintf(buf, sizeof(buf), " rcuc=%lu 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
>
Thank you for the feedback!
> would you like to resend keeping the buffer-overflow fix but leaving
> out the signed-to-unsigned conversion?
>
I will make a second version of the patch, without
conversion as it is intentional.
> However, the signed output is intentional. The idea is that if the
> timekeeping code is confused enough to run the jiffies counter backwards,
> we see a small negative number rather than a huge positive number.
> For example, -132 is immediately obvious, while the 64-bit unsigned
> equivalent of 18446744073709551484 might not be.
I had suspicions that was the case, however, I did not find the pointers
in the code or in the commit message, that it was intentional, so I assumed
a mistake.
Maybe, it would be a good idea for me to add a comment with intent
clarification, to reduce possibility of the same confusion in the future,
while I am at it? If so, should I do it in the same patch, or make a separate one?
On Fri, 29 Mar 2024 20:56:16 +0300
Nikita Kiryushin <[email protected]> wrote:
> Maybe, it would be a good idea for me to add a comment with intent
> clarification, to reduce possibility of the same confusion in the future,
Yes please do.
> while I am at it? If so, should I do it in the same patch, or make a separate one?
I would keep it the same patch, but it really is Paul's decision.
-- Steve
On Fri, Mar 29, 2024 at 02:32:05PM -0400, Steven Rostedt wrote:
> On Fri, 29 Mar 2024 20:56:16 +0300
> Nikita Kiryushin <[email protected]> wrote:
>
> > Maybe, it would be a good idea for me to add a comment with intent
> > clarification, to reduce possibility of the same confusion in the future,
>
> Yes please do.
>
> > while I am at it? If so, should I do it in the same patch, or make a separate one?
>
> I would keep it the same patch, but it really is Paul's decision.
I am with Steve on both questions.
Thanx, Paul
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 <[email protected]>
---
v2: Remove signed to unsigned print format change as
Paul E. McKenney <[email protected]> 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
On Mon, 1 Apr 2024 21:54:54 +0300
Nikita Kiryushin <[email protected]> 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
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 <[email protected]>
---
v3: Change intention comment wording as
Steven Rostedt <[email protected]> suggested
v2: Remove signed to unsigned print format change as
Paul E. McKenney <[email protected]> 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
On Mon, 1 Apr 2024 22:43:15 +0300
Nikita Kiryushin <[email protected]> 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 <[email protected]>
> ---
> v3: Change intention comment wording as
> Steven Rostedt <[email protected]> suggested
> v2: Remove signed to unsigned print format change as
> Paul E. McKenney <[email protected]> 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) <[email protected]>
-- Steve
On Mon, Apr 01, 2024 at 04:03:12PM -0400, Steven Rostedt wrote:
> On Mon, 1 Apr 2024 22:43:15 +0300
> Nikita Kiryushin <[email protected]> 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 <[email protected]>
> > ---
> > v3: Change intention comment wording as
> > Steven Rostedt <[email protected]> suggested
> > v2: Remove signed to unsigned print format change as
> > Paul E. McKenney <[email protected]> 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) <[email protected]>
Queued for v6.10, thank you both!
Thanx, Paul