mm/kasan/report_tags.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (c) 2014 Samsung Electronics Co., Ltd.
   4  * Copyright (c) 2020 Google, Inc.
   5  */
   6
   7 #include <linux/atomic.h>
   8
   9 #include "kasan.h"
  10 #include "../slab.h"
  11
  12 extern struct kasan_stack_ring stack_ring;
  13
  14 static const char *get_common_bug_type(struct kasan_report_info *info)
  15 {
  16         /*
  17          * If access_size is a negative number, then it has reason to be
  18          * defined as out-of-bounds bug type.
  19          *
  20          * Casting negative numbers to size_t would indeed turn up as
  21          * a large size_t and its value will be larger than ULONG_MAX/2,
  22          * so that this can qualify as out-of-bounds.
  23          */
  24         if (info->access_addr + info->access_size < info->access_addr)
  25                 return "out-of-bounds";
  26
  27         return "invalid-access";
  28 }
  29
  30 void kasan_complete_mode_report_info(struct kasan_report_info *info)
  31 {
  32         unsigned long flags;
  33         u64 pos;
  34         struct kasan_stack_ring_entry *entry;
  35         bool alloc_found = false, free_found = false;
  36
  37         if ((!info->cache || !info->object) && !info->bug_type) {
  38                 info->bug_type = get_common_bug_type(info);
  39                 return;
  40         }
  41
  42         write_lock_irqsave(&stack_ring.lock, flags);
  43
  44         pos = atomic64_read(&stack_ring.pos);
  45
  46         /*
  47          * The loop below tries to find stack ring entries relevant to the
  48          * buggy object. This is a best-effort process.
  49          *
  50          * First, another object with the same tag can be allocated in place of
  51          * the buggy object. Also, since the number of entries is limited, the
  52          * entries relevant to the buggy object can be overwritten.
  53          */
  54
  55         for (u64 i = pos - 1; i != pos - 1 - stack_ring.size; i--) {
  56                 if (alloc_found && free_found)
  57                         break;
  58
  59                 entry = &stack_ring.entries[i % stack_ring.size];
  60
  61                 if (kasan_reset_tag(entry->ptr) != info->object ||
  62                     get_tag(entry->ptr) != get_tag(info->access_addr) ||
  63                     info->cache->object_size != entry->size)
  64                         continue;
  65
  66                 if (entry->is_free) {
  67                         /*
  68                          * Second free of the same object.
  69                          * Give up on trying to find the alloc entry.
  70                          */
  71                         if (free_found)
  72                                 break;
  73
  74                         memcpy(&info->free_track, &entry->track,
  75                                sizeof(info->free_track));
  76                         free_found = true;
  77
  78                         /*
  79                          * If a free entry is found first, the bug is likely
  80                          * a use-after-free.
  81                          */
  82                         if (!info->bug_type)
  83                                 info->bug_type = "slab-use-after-free";
  84                 } else {
  85                         /* Second alloc of the same object. Give up. */
  86                         if (alloc_found)
  87                                 break;
  88
  89                         memcpy(&info->alloc_track, &entry->track,
  90                                sizeof(info->alloc_track));
  91                         alloc_found = true;
  92
  93                         /*
  94                          * If an alloc entry is found first, the bug is likely
  95                          * an out-of-bounds.
  96                          */
  97                         if (!info->bug_type)
  98                                 info->bug_type = "slab-out-of-bounds";
  99                 }
 100         }
 101
 102         write_unlock_irqrestore(&stack_ring.lock, flags);
 103
 104         /* Assign the common bug type if no entries were found. */
 105         if (!info->bug_type)
 106                 info->bug_type = get_common_bug_type(info);
 107 }