mm/slub: avoid accessing metadata when pointer is invalid in object_err()

object_err() reports details of an object for further debugging, such as
the freelist pointer, redzone, etc. However, if the pointer is invalid,
attempting to access object metadata can lead to a crash since it does
not point to a valid object.

One known path to the crash is when alloc_consistency_checks()
determines the pointer to the allocated object is invalid because of a
freelist corruption, and calls object_err() to report it. The debug code
should report and handle the corruption gracefully and not crash in the
process.

In case the pointer is NULL or check_valid_pointer() returns false for
the pointer, only print the pointer value and skip accessing metadata.

Fixes: 81819f0fc828 ("SLUB core")
Cc: <stable@vger.kernel.org>
Signed-off-by: Li Qiong <liqiong@nfschina.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

diff --git a/mm/slub.c b/mm/slub.c
index 30003763d224c2704a4b93082b8b47af12dcffc5..1787e4d51e483d1038a9ba9305b1c9a9f3eeb96c 100644 (file)
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1140,7 +1140,12 @@ static void object_err(struct kmem_cache *s, struct slab *slab,
                return;
 
        slab_bug(s, reason);
-       print_trailer(s, slab, object);
+       if (!object || !check_valid_pointer(s, slab, object)) {
+               print_slab_info(slab);
+               pr_err("Invalid pointer 0x%p\n", object);
+       } else {
+               print_trailer(s, slab, object);
+       }
        add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 
        WARN_ON(1);