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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4922fa47d1csm158902215e9.4.2026.06.17.05.06.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2026 05:06:32 -0700 (PDT) From: David Carlier To: syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com Cc: linux-mm@kvack.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, David Carlier Subject: Re: [syzbot] [mm?] KASAN: use-after-free Read in ptdump_pte_entry (2) Date: Wed, 17 Jun 2026 13:06:29 +0100 Message-ID: <20260617120629.160448-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <6a287988.39669fcc.33b062.00a0.GAE@google.com> References: <6a287988.39669fcc.33b062.00a0.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ptdump walks kernel page tables it does not own. While the walk runs, vmalloc can promote a range to a huge PMD (vmap_try_huge_pmd), which collapses the existing PTE table and frees it via pmd_free_pte_page() with no init_mm mmap lock on x86/riscv/powerpc. So ptdump dereferences a just-freed PTE page, hence the UAF in ptdump_pte_entry(). The race is pre-existing; 5ba2f0a15564 only widened the window by deferring the free. Fix posted (v5): defer the kernel page table free by an RCU grace period and walk ptdump under rcu_read_lock(). https://lore.kernel.org/linux-mm/20260617115342.156775-1-devnexen@gmail.com/