From 53ca00a19d345197a37a1bf552e8d1e7b091666c Mon Sep 17 00:00:00 2001 From: Deepanshu Kartikey Date: Wed, 10 Dec 2025 07:50:24 +0530 Subject: [PATCH] mm/slub: reset KASAN tag in defer_free() before accessing freed memory When CONFIG_SLUB_TINY is enabled, kfree_nolock() calls kasan_slab_free() before defer_free(). On ARM64 with MTE (Memory Tagging Extension), kasan_slab_free() poisons the memory and changes the tag from the original (e.g., 0xf3) to a poison tag (0xfe). When defer_free() then tries to write to the freed object to build the deferred free list via llist_add(), the pointer still has the old tag, causing a tag mismatch and triggering a KASAN use-after-free report: BUG: KASAN: slab-use-after-free in defer_free+0x3c/0xbc mm/slub.c:6537 Write at addr f3f000000854f020 by task kworker/u8:6/983 Pointer tag: [f3], memory tag: [fe] Fix this by calling kasan_reset_tag() before accessing the freed memory. This is safe because defer_free() is part of the allocator itself and is expected to manipulate freed memory for bookkeeping purposes. Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Cc: stable@vger.kernel.org Reported-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=7a25305a76d872abcfa1 Tested-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey Acked-by: Alexei Starovoitov Link: https://patch.msgid.link/20251210022024.3255826-1-kartikey406@gmail.com Signed-off-by: Vlastimil Babka --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index f22ba8be29e06..97204d93b1dc1 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -6539,6 +6539,8 @@ static void defer_free(struct kmem_cache *s, void *head) guard(preempt)(); + head = kasan_reset_tag(head); + df = this_cpu_ptr(&defer_free_objects); if (llist_add(head + s->offset, &df->objects)) irq_work_queue(&df->work); -- 2.47.3