From: David Carlier <devnexen@gmail.com>
To: syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, David Carlier <devnexen@gmail.com>
Subject: Re: [syzbot] [mm?] KASAN: use-after-free Read in ptdump_pte_entry (2)
Date: Wed, 17 Jun 2026 13:06:29 +0100 [thread overview]
Message-ID: <20260617120629.160448-1-devnexen@gmail.com> (raw)
In-Reply-To: <6a287988.39669fcc.33b062.00a0.GAE@google.com>
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/
prev parent reply other threads:[~2026-06-17 12:06 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-09 20:37 [syzbot] [mm?] KASAN: use-after-free Read in ptdump_pte_entry (2) syzbot
2026-06-17 12:06 ` David Carlier [this message]
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