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Date:   Sat, 3 Aug 2019 02:19:57 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Laura Abbott <labbott@redhat.com>
cc:     Alexander Potapenko <glider@google.com>,
        kernel test robot <rong.a.chen@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Christoph Lameter <cl@linux.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Kostya Serebryany <kcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Sandeep Patil <sspatil@android.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Jann Horn <jannh@google.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>, LKP <lkp@01.org>,
        linux-mm@kvack.org
Subject: Re: [PATCH] mm: slub: Fix slab walking for init_on_free
In-Reply-To: <20190731193240.29477-1-labbott@redhat.com>
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References:  <20190731193240.29477-1-labbott@redhat.com>
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On Wed, 31 Jul 2019, Laura Abbott wrote:

> To properly clear the slab on free with slab_want_init_on_free,
> we walk the list of free objects using get_freepointer/set_freepointer.
> The value we get from get_freepointer may not be valid. This
> isn't an issue since an actual value will get written later
> but this means there's a chance of triggering a bug if we use
> this value with set_freepointer:
> 
> [    4.478342] kernel BUG at mm/slub.c:306!
> [    4.482437] invalid opcode: 0000 [#1] PREEMPT PTI
> [    4.485750] CPU: 0 PID: 0 Comm: swapper Not tainted 5.2.0-05754-g6471384a #4
> [    4.490635] RIP: 0010:kfree+0x58a/0x5c0
> [    4.493679] Code: 48 83 05 78 37 51 02 01 0f 0b 48 83 05 7e 37 51 02 01 48 83 05 7e 37 51 02 01 48 83 05 7e 37 51 02 01 48 83 05 d6 37 51 02 01 <0f> 0b 48 83 05 d4 37 51 02 01 48 83 05 d4 37 51 02 01 48 83 05 d4
> [    4.506827] RSP: 0000:ffffffff82603d90 EFLAGS: 00010002
> [    4.510475] RAX: ffff8c3976c04320 RBX: ffff8c3976c04300 RCX: 0000000000000000
> [    4.515420] RDX: ffff8c3976c04300 RSI: 0000000000000000 RDI: ffff8c3976c04320
> [    4.520331] RBP: ffffffff82603db8 R08: 0000000000000000 R09: 0000000000000000
> [    4.525288] R10: ffff8c3976c04320 R11: ffffffff8289e1e0 R12: ffffd52cc8db0100
> [    4.530180] R13: ffff8c3976c01a00 R14: ffffffff810f10d4 R15: ffff8c3976c04300
> [    4.535079] FS:  0000000000000000(0000) GS:ffffffff8266b000(0000) knlGS:0000000000000000
> [    4.540628] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    4.544593] CR2: ffff8c397ffff000 CR3: 0000000125020000 CR4: 00000000000406b0
> [    4.549558] Call Trace:
> [    4.551266]  apply_wqattrs_prepare+0x154/0x280
> [    4.554357]  apply_workqueue_attrs_locked+0x4e/0xe0
> [    4.557728]  apply_workqueue_attrs+0x36/0x60
> [    4.560654]  alloc_workqueue+0x25a/0x6d0
> [    4.563381]  ? kmem_cache_alloc_trace+0x1e3/0x500
> [    4.566628]  ? __mutex_unlock_slowpath+0x44/0x3f0
> [    4.569875]  workqueue_init_early+0x246/0x348
> [    4.573025]  start_kernel+0x3c7/0x7ec
> [    4.575558]  x86_64_start_reservations+0x40/0x49
> [    4.578738]  x86_64_start_kernel+0xda/0xe4
> [    4.581600]  secondary_startup_64+0xb6/0xc0
> [    4.584473] Modules linked in:
> [    4.586620] ---[ end trace f67eb9af4d8d492b ]---
> 
> Fix this by ensuring the value we set with set_freepointer is either NULL
> or another value in the chain.
> 
> Reported-by: kernel test robot <rong.a.chen@intel.com>
> Signed-off-by: Laura Abbott <labbott@redhat.com>

Acked-by: David Rientjes <rientjes@google.com>