| Message ID | 20240401185454.361291-1-kiryushin@ancud.ru (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v2] rcu: Fix buffer overlow in print_cpu_stall_info() | expand |
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
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)],
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(-)