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([2405:201:682f:389d:c197:3b05:5401:dca3]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-34a47bdc221sm1601937a91.1.2025.12.09.18.20.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Dec 2025 18:20:35 -0800 (PST) From: Deepanshu Kartikey To: vbabka@suse.cz, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, harry.yoo@oracle.com, ast@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Subject: [PATCH] mm/slub: reset KASAN tag in defer_free() before accessing freed memory Date: Wed, 10 Dec 2025 07:50:24 +0530 Message-ID: <20251210022024.3255826-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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().") Reported-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D7a25305a76d872abcfa1 Tested-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey Acked-by: Alexei Starovoitov --- mm/slub.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index e6a330e24145..46959c6da2cf 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -6534,6 +6534,8 @@ static void defer_free(struct kmem_cache *s, void *he= ad) =20 guard(preempt)(); =20 + head =3D kasan_reset_tag(head); + df =3D this_cpu_ptr(&defer_free_objects); if (llist_add(head + s->offset, &df->objects)) irq_work_queue(&df->work); --=20 2.43.0