On Fri, Aug 01, 2025 at 02:10:36PM +0800, Li Qiong wrote:

For debugging, object_err() prints free pointer of the object. However, if object is a invalid pointer, dereferncing `object + s->offset` can lead to a crash. Therefore, add check_valid_pointer() for the object.

Because this is not only about freelist pointer but also include other metadata, this can be improved a little bit (+ with a slightly more detailed description):

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.

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

Fixes: 81819f0fc828 ("SLUB core")

The tag looks correct.

Cc: stable@vger.kernel.org Signed-off-by: Li Qiong liqiong@nfschina.com

---

v2:

• rephrase the commit message, add comment for object_err().

v3:

• check object pointer in object_err().

v4:

• restore changes in alloc_consistency_checks().

---

mm/slub.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c index 31e11ef256f9..17b91e74f7d9 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1104,7 +1104,11 @@ static void object_err(struct kmem_cache *s, struct slab *slab, return; slab_bug(s, reason);

• print_trailer(s, slab, object);

• if (!check_valid_pointer(s, slab, object)) {

• print_slab_info(slab);
  

• pr_err("invalid object 0x%p\n", object);
  

I thought you were going to update the message above based on previous conversation, "Invalid pointer 0x%p\n"?

• } else

• print_trailer(s, slab, object);
  

Per the coding style guideline [1], an else clause should also use braces { } when the corresponding if clause does.

[1] https://www.kernel.org/doc/html/latest/process/coding-style.html#placing-bra...

add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); WARN_ON(1);