6.9-stable review patch. If anyone has any objections, please let me know.
------------------
From: Nikita Kiryushin kiryushin@ancud.ru
[ Upstream commit 3758f7d9917bd7ef0482c4184c0ad673b4c4e069 ]
The rcuc-starvation output from print_cpu_stall_info() might overflow the buffer if there is a huge difference in jiffies difference. The situation might seem improbable, but computers sometimes get very confused about time, which can result in full-sized integers, and, in this case, buffer overflow.
Also, the unsigned jiffies difference is printed using %ld, which is normally for signed integers. This is intentional for debugging purposes, but it is not obvious from the code.
This commit therefore changes sprintf() to snprintf() and adds a 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 Reviewed-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Uladzislau Rezki (Sony) urezki@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 5d666428546b0..b5ec62b2d850a 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 values indicate a probable 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)],