Re: [PATCH] arm64/crypto: poly1305 fix a read out-of-bound

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Jul 12, 2022 at 11:32:15AM +0800, GUO Zihua wrote:
> A kasan error was reported during fuzzing:
> 
> BUG: KASAN: slab-out-of-bounds in neon_poly1305_blocks.constprop.0+0x1b4/0x250 [poly1305_neon]
> Read of size 4 at addr ffff0010e293f010 by task syz-executor.5/1646715
> CPU: 4 PID: 1646715 Comm: syz-executor.5 Kdump: loaded Not tainted 5.10.0.aarch64 #1
> Hardware name: Huawei TaiShan 2280 /BC11SPCD, BIOS 1.59 01/31/2019
> Call trace:
>  dump_backtrace+0x0/0x394
>  show_stack+0x34/0x4c arch/arm64/kernel/stacktrace.c:196
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x158/0x1e4 lib/dump_stack.c:118
>  print_address_description.constprop.0+0x68/0x204 mm/kasan/report.c:387
>  __kasan_report+0xe0/0x140 mm/kasan/report.c:547
>  kasan_report+0x44/0xe0 mm/kasan/report.c:564
>  check_memory_region_inline mm/kasan/generic.c:187 [inline]
>  __asan_load4+0x94/0xd0 mm/kasan/generic.c:252
>  neon_poly1305_blocks.constprop.0+0x1b4/0x250 [poly1305_neon]
>  neon_poly1305_do_update+0x6c/0x15c [poly1305_neon]
>  neon_poly1305_update+0x9c/0x1c4 [poly1305_neon]
>  crypto_shash_update crypto/shash.c:131 [inline]
>  shash_finup_unaligned+0x84/0x15c crypto/shash.c:179
>  crypto_shash_finup+0x8c/0x140 crypto/shash.c:193
>  shash_digest_unaligned+0xb8/0xe4 crypto/shash.c:201
>  crypto_shash_digest+0xa4/0xfc crypto/shash.c:217
>  crypto_shash_tfm_digest+0xb4/0x150 crypto/shash.c:229
>  essiv_skcipher_setkey+0x164/0x200 [essiv]
>  crypto_skcipher_setkey+0xb0/0x160 crypto/skcipher.c:612
>  skcipher_setkey+0x3c/0x50 crypto/algif_skcipher.c:305
>  alg_setkey+0x114/0x2a0 crypto/af_alg.c:220
>  alg_setsockopt+0x19c/0x210 crypto/af_alg.c:253
>  __sys_setsockopt+0x190/0x2e0 net/socket.c:2123
>  __do_sys_setsockopt net/socket.c:2134 [inline]
>  __se_sys_setsockopt net/socket.c:2131 [inline]
>  __arm64_sys_setsockopt+0x78/0x94 net/socket.c:2131
>  __invoke_syscall arch/arm64/kernel/syscall.c:36 [inline]
>  invoke_syscall+0x64/0x100 arch/arm64/kernel/syscall.c:48
>  el0_svc_common.constprop.0+0x220/0x230 arch/arm64/kernel/syscall.c:155
>  do_el0_svc+0xb4/0xd4 arch/arm64/kernel/syscall.c:217
>  el0_svc+0x24/0x3c arch/arm64/kernel/entry-common.c:353
>  el0_sync_handler+0x160/0x164 arch/arm64/kernel/entry-common.c:369
>  el0_sync+0x160/0x180 arch/arm64/kernel/entry.S:683
> 
> This error can be reproduced by the following code compiled as ko on a
> system with kasan enabled:
> 
> char test_data[] = "\x00\x01\x02\x03\x04\x05\x06\x07"
> 		   "\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f"
> 		   "\x10\x11\x12\x13\x14\x15\x16\x17"
> 		   "\x18\x19\x1a\x1b\x1c\x1d\x1e";
> 
> int init(void)
> {
> 	struct crypto_shash *tfm = NULL;
> 	struct shash_desc *desc = NULL;
> 	char *data = NULL;
> 
> 	tfm = crypto_alloc_shash("poly1305", 0, 0);
> 	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(tfm), GFP_KERNEL);
> 	desc->tfm = tfm;
> 
> 	data = kmalloc(POLY1305_KEY_SIZE - 1, GFP_KERNEL);
> 	memcpy(data, test_data, POLY1305_KEY_SIZE - 1);
> 	crypto_shash_update(desc, data, POLY1305_KEY_SIZE - 1);
> 	crypto_shash_final(desc, data);
> 	kfree(data);
> 	return 0;
> }
> 
> void deinit(void)
> {
> }
> 
> module_init(init)
> module_exit(deinit)
> MODULE_LICENSE("GPL");
> 
> The root cause of the bug sits in neon_poly1305_blocks. The logic
> neon_poly1305_blocks() performed is that if it was called with both s[]
> and r[] uninitialized, it will first try to initialize them with the
> data from the first "block" that it believed to be 32 bytes in length.
> First 16 bytes are used as the key and the next 16 bytes for s[]. This
> would lead to the aforementioned read out-of-bound. However, after
> calling poly1305_init_arch(), only 16 bytes were deducted from the input
> and s[] is initialized yet again with the following 16 bytes. The second
> initialization of s[] is certainly redundent which indicates that the
> first initialization should be for r[] only.
> 
> This patch fixes the issue by calling poly1305_init_arm64() instead of
> poly1305_init_arch(). This is also the implementation for the same
> algorithm on arm platform.
> 
> Signed-off-by: GUO Zihua <guozihua@huawei.com>

Is the special reproducer really needed?  I'd expect this to be reproduced by
the existing crypto self-tests just by booting a kernel built with both
CONFIG_KASAN=y and CONFIG_CRYPTO_MANAGER_EXTRA_TESTS=y.

Also, despite the verbosity of the commit message, it doesn't include the two
things that really matter, which are a Fixes tag and Cc stable.

- Eric