From 8f17febb34ceb464e3ff99e9436d0ae3f47b4862 Mon Sep 17 00:00:00 2001 From: Kuan-Ying Lee Date: Sun, 29 Jan 2023 10:14:35 +0800 Subject: kasan: infer allocation size by scanning metadata Make KASAN scan metadata to infer the requested allocation size instead of printing cache->object_size. This patch fixes confusing slab-out-of-bounds reports as reported in: https://bugzilla.kernel.org/show_bug.cgi?id=216457 As an example of the confusing behavior, the report below hints that the allocation size was 192, while the kernel actually called kmalloc(184): ================================================================== BUG: KASAN: slab-out-of-bounds in _find_next_bit+0x143/0x160 lib/find_bit.c:109 Read of size 8 at addr ffff8880175766b8 by task kworker/1:1/26 ... The buggy address belongs to the object at ffff888017576600 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 184 bytes inside of 192-byte region [ffff888017576600, ffff8880175766c0) ... Memory state around the buggy address: ffff888017576580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff888017576600: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffff888017576680: 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc ^ ffff888017576700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff888017576780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ================================================================== With this patch, the report shows: ================================================================== ... The buggy address belongs to the object at ffff888017576600 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 0 bytes to the right of allocated 184-byte region [ffff888017576600, ffff8880175766b8) ... ================================================================== Also report slab use-after-free bugs as "slab-use-after-free" and print "freed" instead of "allocated" in the report when describing the accessed memory region. Also improve the metadata-related comment in kasan_find_first_bad_addr and use addr_has_metadata across KASAN code instead of open-coding KASAN_SHADOW_START checks. [akpm@linux-foundation.org: fix printk warning] Link: https://bugzilla.kernel.org/show_bug.cgi?id=216457 Link: https://lkml.kernel.org/r/20230129021437.18812-1-Kuan-Ying.Lee@mediatek.com Signed-off-by: Kuan-Ying Lee Co-developed-by: Andrey Konovalov Cc: Alexander Potapenko Cc: Andrey Ryabinin Cc: Chinwen Chang Cc: Dmitry Vyukov Cc: Matthias Brugger Cc: Qun-Wei Lin Cc: Vincenzo Frascino Signed-off-by: Andrew Morton --- mm/kasan/report.c | 41 ++++++++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 11 deletions(-) (limited to 'mm/kasan/report.c') diff --git a/mm/kasan/report.c b/mm/kasan/report.c index 22598b20c7b7..89078f912827 100644 --- a/mm/kasan/report.c +++ b/mm/kasan/report.c @@ -231,33 +231,46 @@ static inline struct page *addr_to_page(const void *addr) return NULL; } -static void describe_object_addr(const void *addr, struct kmem_cache *cache, - void *object) +static void describe_object_addr(const void *addr, struct kasan_report_info *info) { unsigned long access_addr = (unsigned long)addr; - unsigned long object_addr = (unsigned long)object; - const char *rel_type; + unsigned long object_addr = (unsigned long)info->object; + const char *rel_type, *region_state = ""; int rel_bytes; pr_err("The buggy address belongs to the object at %px\n" " which belongs to the cache %s of size %d\n", - object, cache->name, cache->object_size); + info->object, info->cache->name, info->cache->object_size); if (access_addr < object_addr) { rel_type = "to the left"; rel_bytes = object_addr - access_addr; - } else if (access_addr >= object_addr + cache->object_size) { + } else if (access_addr >= object_addr + info->alloc_size) { rel_type = "to the right"; - rel_bytes = access_addr - (object_addr + cache->object_size); + rel_bytes = access_addr - (object_addr + info->alloc_size); } else { rel_type = "inside"; rel_bytes = access_addr - object_addr; } + /* + * Tag-Based modes use the stack ring to infer the bug type, but the + * memory region state description is generated based on the metadata. + * Thus, defining the region state as below can contradict the metadata. + * Fixing this requires further improvements, so only infer the state + * for the Generic mode. + */ + if (IS_ENABLED(CONFIG_KASAN_GENERIC)) { + if (strcmp(info->bug_type, "slab-out-of-bounds") == 0) + region_state = "allocated "; + else if (strcmp(info->bug_type, "slab-use-after-free") == 0) + region_state = "freed "; + } + pr_err("The buggy address is located %d bytes %s of\n" - " %d-byte region [%px, %px)\n", - rel_bytes, rel_type, cache->object_size, (void *)object_addr, - (void *)(object_addr + cache->object_size)); + " %s%zu-byte region [%px, %px)\n", + rel_bytes, rel_type, region_state, info->alloc_size, + (void *)object_addr, (void *)(object_addr + info->alloc_size)); } static void describe_object_stacks(struct kasan_report_info *info) @@ -279,7 +292,7 @@ static void describe_object(const void *addr, struct kasan_report_info *info) { if (kasan_stack_collection_enabled()) describe_object_stacks(info); - describe_object_addr(addr, info->cache, info->object); + describe_object_addr(addr, info); } static inline bool kernel_or_module_addr(const void *addr) @@ -436,6 +449,12 @@ static void complete_report_info(struct kasan_report_info *info) if (slab) { info->cache = slab->slab_cache; info->object = nearest_obj(info->cache, slab, addr); + + /* Try to determine allocation size based on the metadata. */ + info->alloc_size = kasan_get_alloc_size(info->object, info->cache); + /* Fallback to the object size if failed. */ + if (!info->alloc_size) + info->alloc_size = info->cache->object_size; } else info->cache = info->object = NULL; -- cgit v1.2.3