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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 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 40A791C0013 X-Stat-Signature: e1hbxbzb5a65y5c96ouj7nafwexbxgzt X-Rspam-User: X-HE-Tag: 1765333238-655602 X-HE-Meta: U2FsdGVkX1+aGH4IYn+KLNhle/7zmBViOKl5wSe9OqXlVsrEAvf86feOe6igy/m5CCtBzzc3ddYv1tZYoF9vG5qBoSrKDqxJprJAZKMeW+C3ulSnfu8J8D1V+EUdN7EVieGvLyi/MpSBuAN2+fjj9J2qHGqM4IaWtw2wvkAadPg6Jd+HY5oz4MguAboELvmcMHAxNz1VFt7cjbhgmVoriMu3klBmpmVxmglVPTnhUPsLaDqb60PKIl6SUisSPLBLBXJW2jcknDS3VeX8/2inWkCgHfPw8Ad4IYXJFAF/VAMIg3hivayNecmrZbrIfOmEiYgI3J7sfPaT24T+47/nA1IHJc9IBytoeBie1ISXNsEMMi7INSdIy4fBWX46UpQ6/ew7etdinXnREoZzayKhCvX8uYnfvAuAYUbPRcFXM71eCEGHUNLV2BdlWBcIyg69E3AufsuvFQ9SpKpd0JSPl9bAuyV58a0aXwXFojq6Xu0ejGMsEec1iZcQoNcd7iAOG2qd5vsXL6LcReiKVENA615Cxtm7/z/dcKgZc3GKAoPP3crK3RYnK2oowxTYNeiV7dffX+4E+4PzpiCDCuKMjqkVuWsACD6f8J7e0gsEpfjWr1rm65kSxTG5aFKVLqNkT6yBWSVqQBrr5eIi15IjO3cpDH/o+fdiikMDq1DnXRAiEy83uwQs74+wU3PcFjaSqWN3O3QcAwAQrQGmPT8YU3aLF+jtWgflJKRKklbLfKuXhBWUs6YMb7PxT1KOGmGxlf8ZZcwJmmqYmAouAz4diqPaIOsUiRlwmihWIp1DpHMvf9CDLMk6aNk1nqqJoKEucJXdWoMxmlDkcNbilU+apK2TCYx4pO7Sqsag206l+U37/YzElZ2fBwfKuij4OvS8iI99MacA9HTEZJkneJHT+5PhSu/IeQtHRZYEE10TyoVtyfzHA8dZbQ9lMtW60ARyz71cUjTwxYn+EHEyGuw +z4Vr8s4 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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=7a25305a76d872abcfa1 Tested-by: syzbot+7a25305a76d872abcfa1@syzkaller.appspotmail.com Signed-off-by: Deepanshu Kartikey --- 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 *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); -- 2.43.0