kasan: better identify bug types for tag-based modes

Identify the bug type for the tag-based modes based on the stack trace
entries found in the stack ring.

If a free entry is found first (meaning that it was added last), mark the
bug as use-after-free.  If an alloc entry is found first, mark the bug as
slab-out-of-bounds.  Otherwise, assign the common bug type.

This change returns the functionalify of the previously dropped
CONFIG_KASAN_TAGS_IDENTIFY.

Link: https://lkml.kernel.org/r/13ce7fa07d9d995caedd1439dfae4d51401842f2.1662411800.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Peter Collingbourne <pcc@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
index 57f7355..d351042 100644 (file)
--- a/mm/kasan/report_tags.c
+++ b/mm/kasan/report_tags.c
@@ -10,7 +10,7 @@
 
 extern struct kasan_stack_ring stack_ring;
 
-static const char *get_bug_type(struct kasan_report_info *info)
+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
@@ -37,9 +37,8 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
        bool is_free;
        bool alloc_found = false, free_found = false;
 
-       info->bug_type = get_bug_type(info);
-
-       if (!info->cache || !info->object)
+       if (!info->cache || !info->object) {
+               info->bug_type = get_common_bug_type(info);
                return;
        }
 
@@ -84,6 +83,13 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
                        info->free_track.pid = pid;
                        info->free_track.stack = stack;
                        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 = "use-after-free";
                } else {
                        /* Second alloc of the same object. Give up. */
                        if (alloc_found)
@@ -92,8 +98,19 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
                        info->alloc_track.pid = pid;
                        info->alloc_track.stack = stack;
                        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);
 }