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Date: Mon, 21 Dec 2015 22:32:49 +0100
From: Stephan Mueller <smueller@...onox.de>
To: Dmitry Vyukov <dvyukov@...gle.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>,
"David S. Miller" <davem@...emloft.net>,
linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
syzkaller <syzkaller@...glegroups.com>,
Kostya Serebryany <kcc@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Sasha Levin <sasha.levin@...cle.com>,
Kees Cook <keescook@...gle.com>
Subject: Re: use-after-free in skcipher_sock_destruct
Am Donnerstag, 17. Dezember 2015, 13:56:12 schrieb Dmitry Vyukov:
Hi Dmitry,
> Hello,
>
> The following program triggers use-after-free in skcipher_sock_destruct:
This issue is not evident after applying Herbert's patch converting the
algif_skcipher from using ablkcipher to skcipher API.
>
> // autogenerated by syzkaller (http://github.com/google/syzkaller)
> #include <syscall.h>
> #include <string.h>
> #include <stdint.h>
> #include <sys/types.h>
> #include <sys/socket.h>
> #include <pthread.h>
>
> struct sockaddr_alg {
> unsigned short salg_family;
> char salg_type[14];
> unsigned salg_feat;
> unsigned salg_mask;
> char salg_name[64];
> };
>
> int fd;
>
> void *thr0(void *arg)
> {
> struct sockaddr_alg sa = {};
> sa.salg_family = 0x26;
> memcpy(sa.salg_type,
> "\x73\x6b\x63\x69\x70\x68\x65\x72\x00\x00\x00\x00\x00\x00", 14);
> sa.salg_feat = 0xf;
> sa.salg_mask = 0x100;
> memcpy(sa.salg_name,
> "\x65\x63\x62\x28\x73\x65\x72\x70\x65\x6e\x74\x29\x00\x00\x00\x00\x00\x00\x0
> 0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0
> 0\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x0
> 0\x00\x00\x00\x00\x00\x00\x00", 64);
> bind(fd, (struct sockaddr*)&sa, sizeof(sa));
> return 0;
> }
>
> void *thr1(void *arg)
> {
> accept4(fd, 0, 0, 0x800ul);
> return 0;
> }
>
> int main()
> {
> fd = socket(PF_ALG, SOCK_SEQPACKET, 0);
> pthread_t th[4];
> pthread_create(&th[0], 0, thr0, 0);
> pthread_create(&th[1], 0, thr1, 0);
> pthread_create(&th[2], 0, thr0, 0);
> pthread_create(&th[3], 0, thr1, 0);
> pthread_join(th[0], 0);
> pthread_join(th[1], 0);
> pthread_join(th[2], 0);
> pthread_join(th[3], 0);
> return 0;
> }
>
>
> ==================================================================
> BUG: KASAN: use-after-free in skcipher_sock_destruct+0x39c/0x3e0 at
> addr ffff8800387a2d38
> Read of size 4 by task executor/27423
> ============================================================================
> = BUG kmalloc-96 (Not tainted): kasan: bad access detected
> ----------------------------------------------------------------------------
> -
>
> Disabling lock debugging due to kernel taint
> INFO: Allocated in __crypto_alloc_tfm+0xd9/0x470 age=36 cpu=0 pid=27396
> [< none >] __kmalloc+0x2d9/0x480 mm/slub.c:3532
> [< inline >] kmalloc include/linux/slab.h:463
> [< inline >] kzalloc include/linux/slab.h:602
> [< none >] __crypto_alloc_tfm+0xd9/0x470 crypto/api.c:374
> [< none >] crypto_alloc_ablkcipher+0x7b/0x1f0
> crypto/ablkcipher.c:699 [< none >] skcipher_bind+0x25/0x30
> crypto/algif_skcipher.c:754 [< none >] alg_bind+0x1a9/0x410
> crypto/af_alg.c:155
> [< none >] SYSC_bind+0x20a/0x2c0 net/socket.c:1383
> [< none >] SyS_bind+0x24/0x30 net/socket.c:1369
> [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
>
> INFO: Freed in kzfree+0x28/0x30 age=26 cpu=2 pid=27421
> [< none >] kfree+0x26f/0x3e0 mm/slub.c:3632
> [< none >] kzfree+0x28/0x30 mm/slab_common.c:1270
> [< none >] crypto_destroy_tfm+0xdd/0x1e0 crypto/api.c:596
> [< inline >] crypto_free_tfm include/linux/crypto.h:623
> [< inline >] crypto_free_ablkcipher include/linux/crypto.h:769
> [< none >] skcipher_release+0x18/0x20 crypto/algif_skcipher.c:759
> [< inline >] alg_do_release crypto/af_alg.c:116
> [< none >] alg_bind+0x26a/0x410 crypto/af_alg.c:170
> [< none >] SYSC_bind+0x20a/0x2c0 net/socket.c:1383
> [< none >] SyS_bind+0x24/0x30 net/socket.c:1369
> [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a
> arch/x86/entry/entry_64.S:185
>
> INFO: Slab 0xffffea0000e1e880 objects=19 used=8 fp=0xffff8800387a3380
> flags=0x1fffc0000004080
> INFO: Object 0xffff8800387a2d00 @offset=3328 fp=0xffff8800387a3520
> CPU: 0 PID: 27423 Comm: executor Tainted: G B 4.4.0-rc3+ #151
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> 0000000000000000 ffff880035c67700 ffffffff82e0f4b8 0000000041b58ab3
> ffffffff87a9a265 ffffffff82e0f406 ffff880037f15a00 ffffffff87abb3aa
> ffff88003e804780 0000000000000008 ffff8800387a2d00 ffff880035c67700
>
> Call Trace:
> [<ffffffff81845754>] __asan_report_load4_noabort+0x54/0x70
> mm/kasan/report.c:294
> [< inline >] crypto_ablkcipher_ivsize include/linux/crypto.h:807
> [<ffffffff82d2d3bc>] skcipher_sock_destruct+0x39c/0x3e0
> crypto/algif_skcipher.c:787
> [<ffffffff856c9255>] sk_destruct+0xa5/0x5f0 net/core/sock.c:1446
> [<ffffffff856c982c>] __sk_free+0x8c/0x260 net/core/sock.c:1474
> [<ffffffff856c9a30>] sk_free+0x30/0x40 net/core/sock.c:1485
> [< inline >] sock_put include/net/sock.h:1625
> [<ffffffff82d26c50>] af_alg_release+0x60/0x90 crypto/af_alg.c:123
> [<ffffffff856b06b6>] sock_release+0x96/0x260 net/socket.c:571
> [<ffffffff856b0896>] sock_close+0x16/0x20 net/socket.c:1022
> [<ffffffff8189d9e4>] __fput+0x244/0x860 fs/file_table.c:208
> [<ffffffff8189e095>] ____fput+0x15/0x20 fs/file_table.c:244
> [<ffffffff813e34d0>] task_work_run+0x130/0x240 kernel/task_work.c:115
> [< inline >] exit_task_work include/linux/task_work.h:21
> [<ffffffff8137d8f5>] do_exit+0x885/0x3050 kernel/exit.c:750
> [<ffffffff8138021c>] do_group_exit+0xec/0x390 kernel/exit.c:880
> [<ffffffff813ab067>] get_signal+0x677/0x1bf0 kernel/signal.c:2307
> [<ffffffff8118645e>] do_signal+0x7e/0x2170 arch/x86/kernel/signal.c:709
> [<ffffffff81003a1e>] exit_to_usermode_loop+0xfe/0x1e0
> arch/x86/entry/common.c:247
> [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:282
> [<ffffffff8100733b>] syscall_return_slowpath+0x16b/0x240
> arch/x86/entry/common.c:344
> [<ffffffff86a8a122>] int_ret_from_sys_call+0x25/0x9f
> arch/x86/entry/entry_64.S:281
> ==================================================================
>
> On upstream commit 31ade3b83e1821da5fbb2f11b5b3d4ab2ec39db8 (Nov 29).
> --
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--
Ciao
Stephan
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