On Mon, 1 Apr 2024 22:43:15 +0300
Nikita Kiryushin <kiryushin@xxxxxxxx> 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@xxxxxxxx>
> ---
> v3: Change intention comment wording as
> Steven Rostedt <rostedt@xxxxxxxxxxx> suggested
> v2: Remove signed to unsigned print format change as
> Paul E. McKenney <paulmck@xxxxxxxxxx> 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@xxxxxxxxxxx>
-- Steve
