refscale: Check that nreaders and loops multiplication doesn't overflow

The nreaders and loops variables are exposed as module parameters, which,
in certain combinations, can lead to multiplication overflow.

Besides, loops parameter is defined as long, while through the code is
used as int, which can cause truncation on 64-bit kernels and possible
zeroes where they shouldn't appear.

Since code uses result of multiplication as int anyway, it only makes sense
to replace loops with int. Multiplication overflow check is also added
due to possible multiplication between two very big numbers.

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

Fixes: 653ed64 ("refperf: Add a test to measure performance of read-side synchronization")
Signed-off-by: Artem Sadovnikov <[email protected]>
Signed-off-by: Neeraj Upadhyay (AMD) <[email protected]>

Author: Artem Sadovnikov

kernel/rcu/refscale.c

@@ -85,7 +85,7 @@ torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0,
 // Number of typesafe_lookup structures, that is, the degree of concurrency.
 torture_param(long, lookup_instances, 0, "Number of typesafe_lookup structures.");
 // Number of loops per experiment, all readers execute operations concurrently.
-torture_param(long, loops, 10000, "Number of loops per experiment.");
+torture_param(int, loops, 10000, "Number of loops per experiment.");
 // Number of readers, with -1 defaulting to about 75% of the CPUs.
 torture_param(int, nreaders, -1, "Number of readers, -1 for 75% of CPUs.");
 // Number of runs.
@@ -1140,7 +1140,7 @@ static void
 ref_scale_print_module_parms(const struct ref_scale_ops *cur_ops, const char *tag)
 {
 	pr_alert("%s" SCALE_FLAG
-		 "--- %s:  verbose=%d verbose_batched=%d shutdown=%d holdoff=%d lookup_instances=%ld loops=%ld nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
+		 "--- %s:  verbose=%d verbose_batched=%d shutdown=%d holdoff=%d lookup_instances=%ld loops=%d nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag,
 		 verbose, verbose_batched, shutdown, holdoff, lookup_instances, loops, nreaders, nruns, readdelay);
 }
 
@@ -1238,12 +1238,16 @@ ref_scale_init(void)
 	// Reader tasks (default to ~75% of online CPUs).
 	if (nreaders < 0)
 		nreaders = (num_online_cpus() >> 1) + (num_online_cpus() >> 2);
-	if (WARN_ONCE(loops <= 0, "%s: loops = %ld, adjusted to 1\n", __func__, loops))
+	if (WARN_ONCE(loops <= 0, "%s: loops = %d, adjusted to 1\n", __func__, loops))
 		loops = 1;
 	if (WARN_ONCE(nreaders <= 0, "%s: nreaders = %d, adjusted to 1\n", __func__, nreaders))
 		nreaders = 1;
 	if (WARN_ONCE(nruns <= 0, "%s: nruns = %d, adjusted to 1\n", __func__, nruns))
 		nruns = 1;
+	if (WARN_ONCE(loops > INT_MAX / nreaders,
+		      "%s: nreaders * loops will overflow, adjusted loops to %d",
+		      __func__, INT_MAX / nreaders))
+		loops = INT_MAX / nreaders;
 	reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]),
 			       GFP_KERNEL);
 	if (!reader_tasks) {