Commit 4ecd9542 authored by Matthew Wilcox's avatar Matthew Wilcox
Browse files

ida: Free correct IDA bitmap 



There's a relatively rare race where we look at the per-cpu preallocated
IDA bitmap, see it's NULL, allocate a new one, and atomically update it.
If the kmalloc() happened to sleep and we were rescheduled to a different
CPU, or an interrupt came in at the exact right time, another task
might have successfully allocated a bitmap and already deposited it.
I forgot what the semantics of cmpxchg() were and ended up freeing the
wrong bitmap leading to KASAN reporting a use-after-free.

Dmitry found the bug with syzkaller & wrote the patch.  I wrote the test
case that will reproduce the bug without his patch being applied.

Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
parent 3f1b6f9d

lib/radix-tree.c

+2 −2
Original line number Diff line number Diff line
@@ -2129,7 +2129,7 @@ int ida_pre_get(struct ida *ida, gfp_t gfp) 
		struct ida_bitmap *bitmap = kmalloc(sizeof(*bitmap), gfp);

		if (!bitmap)

			return 0;

		bitmap = this_cpu_cmpxchg(ida_bitmap, NULL, bitmap);

		if (this_cpu_cmpxchg(ida_bitmap, NULL, bitmap))

			kfree(bitmap);

	}

tools/testing/radix-tree/idr-test.c

+31 −3
Original line number Diff line number Diff line
@@ -363,7 +363,7 @@ void ida_check_random(void) 
{

	DEFINE_IDA(ida);

	DECLARE_BITMAP(bitmap, 2048);

	int id;

	int id, err;

	unsigned int i;

	time_t s = time(NULL);
@@ -377,8 +377,11 @@ void ida_check_random(void) 
			ida_remove(&ida, bit);

		} else {

			__set_bit(bit, bitmap);

			do {

				ida_pre_get(&ida, GFP_KERNEL);

			assert(!ida_get_new_above(&ida, bit, &id));

				err = ida_get_new_above(&ida, bit, &id);

			} while (err == -ENOMEM);

			assert(!err);

			assert(id == bit);

		}

	}
@@ -476,11 +479,36 @@ void ida_checks(void) 
	radix_tree_cpu_dead(1);

}



static void *ida_random_fn(void *arg)

{

	rcu_register_thread();

	ida_check_random();

	rcu_unregister_thread();

	return NULL;

}



void ida_thread_tests(void)

{

	pthread_t threads[10];

	int i;



	for (i = 0; i < ARRAY_SIZE(threads); i++)

		if (pthread_create(&threads[i], NULL, ida_random_fn, NULL)) {

			perror("creating ida thread");

			exit(1);

		}



	while (i--)

		pthread_join(threads[i], NULL);

}



int __weak main(void)

{

	radix_tree_init();

	idr_checks();

	ida_checks();

	ida_thread_tests();

	radix_tree_cpu_dead(1);

	rcu_barrier();

	if (nr_allocated)

		printf("nr_allocated = %d\n", nr_allocated);

tools/testing/radix-tree/main.c

+1 −0
Original line number Diff line number Diff line
@@ -368,6 +368,7 @@ int main(int argc, char **argv) 
	iteration_test(0, 10 + 90 * long_run);

	iteration_test(7, 10 + 90 * long_run);

	single_thread_tests(long_run);

	ida_thread_tests();



	/* Free any remaining preallocated nodes */

	radix_tree_cpu_dead(0);

tools/testing/radix-tree/test.h

+1 −0
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ void iteration_test(unsigned order, unsigned duration); 
void benchmark(void);

void idr_checks(void);

void ida_checks(void);

void ida_thread_tests(void);



struct item *

item_tag_set(struct radix_tree_root *root, unsigned long index, int tag);

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