mm/kasan/report_tags.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2014 Samsung Electronics Co., Ltd.
 * Copyright (c) 2020 Google, Inc.
 */

#include <linux/atomic.h>

#include "kasan.h"
#include "../slab.h"

extern struct kasan_stack_ring stack_ring;

static const char *get_common_bug_type(struct kasan_report_info *info)
{
	/*
	 * If access_size is a negative number, then it has reason to be
	 * defined as out-of-bounds bug type.
	 *
	 * Casting negative numbers to size_t would indeed turn up as
	 * a large size_t and its value will be larger than ULONG_MAX/2,
	 * so that this can qualify as out-of-bounds.
	 */
	if (info->access_addr + info->access_size < info->access_addr)
		return "out-of-bounds";

	return "invalid-access";
}

void kasan_complete_mode_report_info(struct kasan_report_info *info)
{
	unsigned long flags;
	u64 pos;
	struct kasan_stack_ring_entry *entry;
	bool alloc_found = false, free_found = false;

	if ((!info->cache || !info->object) && !info->bug_type) {
		info->bug_type = get_common_bug_type(info);
		return;
	}

	write_lock_irqsave(&stack_ring.lock, flags);

	pos = atomic64_read(&stack_ring.pos);

	/*
	 * The loop below tries to find stack ring entries relevant to the
	 * buggy object. This is a best-effort process.
	 *
	 * First, another object with the same tag can be allocated in place of
	 * the buggy object. Also, since the number of entries is limited, the
	 * entries relevant to the buggy object can be overwritten.
	 */

	for (u64 i = pos - 1; i != pos - 1 - stack_ring.size; i--) {
		if (alloc_found && free_found)
			break;

		entry = &stack_ring.entries[i % stack_ring.size];

		if (kasan_reset_tag(entry->ptr) != info->object ||
		    get_tag(entry->ptr) != get_tag(info->access_addr) ||
		    info->cache->object_size != entry->size)
			continue;

		if (entry->is_free) {
			/*
			 * Second free of the same object.
			 * Give up on trying to find the alloc entry.
			 */
			if (free_found)
				break;

			memcpy(&info->free_track, &entry->track,
			       sizeof(info->free_track));
			free_found = true;

			/*
			 * If a free entry is found first, the bug is likely
			 * a use-after-free.
			 */
			if (!info->bug_type)
				info->bug_type = "slab-use-after-free";
		} else {
			/* Second alloc of the same object. Give up. */
			if (alloc_found)
				break;

			memcpy(&info->alloc_track, &entry->track,
			       sizeof(info->alloc_track));
			alloc_found = true;

			/*
			 * If an alloc entry is found first, the bug is likely
			 * an out-of-bounds.
			 */
			if (!info->bug_type)
				info->bug_type = "slab-out-of-bounds";
		}
	}

	write_unlock_irqrestore(&stack_ring.lock, flags);

	/* Assign the common bug type if no entries were found. */
	if (!info->bug_type)
		info->bug_type = get_common_bug_type(info);
}