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Subject[PATCH 4.9 62/72] crypto: dh - Dont permit p to be 0
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Biggers <ebiggers@google.com>

commit 199512b1234f09e44d592153ec82b44212b2f0c4 upstream.

If 'p' is 0 for the software Diffie-Hellman implementation, then
dh_max_size() returns 0. In the case of KEYCTL_DH_COMPUTE, this causes
ZERO_SIZE_PTR to be passed to sg_init_one(), which with
CONFIG_DEBUG_SG=y triggers the 'BUG_ON(!virt_addr_valid(buf));' in
sg_set_buf().

Fix this by making crypto_dh_decode_key() reject 0 for 'p'. p=0 makes
no sense for any DH implementation because 'p' is supposed to be a prime
number. Moreover, 'mod 0' is not mathematically defined.

Bug report:

kernel BUG at ./include/linux/scatterlist.h:140!
invalid opcode: 0000 [#1] SMP KASAN
CPU: 0 PID: 27112 Comm: syz-executor2 Not tainted 4.14.0-rc7-00010-gf5dbb5d0ce32-dirty #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.3-20171021_125229-anatol 04/01/2014
task: ffff88006caac0c0 task.stack: ffff88006c7c8000
RIP: 0010:sg_set_buf include/linux/scatterlist.h:140 [inline]
RIP: 0010:sg_init_one+0x1b3/0x240 lib/scatterlist.c:156
RSP: 0018:ffff88006c7cfb08 EFLAGS: 00010216
RAX: 0000000000010000 RBX: ffff88006c7cfe30 RCX: 00000000000064ee
RDX: ffffffff81cf64c3 RSI: ffffc90000d72000 RDI: ffffffff92e937e0
RBP: ffff88006c7cfb30 R08: ffffed000d8f9fab R09: ffff88006c7cfd30
R10: 0000000000000005 R11: ffffed000d8f9faa R12: ffff88006c7cfd30
R13: 0000000000000000 R14: 0000000000000010 R15: ffff88006c7cfc50
FS: 00007fce190fa700(0000) GS:ffff88003ea00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fffc6b33db8 CR3: 000000003cf64000 CR4: 00000000000006f0
Call Trace:
__keyctl_dh_compute+0xa95/0x19b0 security/keys/dh.c:360
keyctl_dh_compute+0xac/0x100 security/keys/dh.c:434
SYSC_keyctl security/keys/keyctl.c:1745 [inline]
SyS_keyctl+0x72/0x2c0 security/keys/keyctl.c:1641
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x4585c9
RSP: 002b:00007fce190f9bd8 EFLAGS: 00000216 ORIG_RAX: 00000000000000fa
RAX: ffffffffffffffda RBX: 0000000000738020 RCX: 00000000004585c9
RDX: 000000002000d000 RSI: 0000000020000ff4 RDI: 0000000000000017
RBP: 0000000000000046 R08: 0000000020008000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 00007fff6e610cde
R13: 00007fff6e610cdf R14: 00007fce190fa700 R15: 0000000000000000
Code: 03 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 33 5b 45 89 6c 24 14 41 5c 41 5d 41 5e 41 5f 5d c3 e8 fd 8f 68 ff <0f> 0b e8 f6 8f 68 ff 0f 0b e8 ef 8f 68 ff 0f 0b e8 e8 8f 68 ff 20
RIP: sg_set_buf include/linux/scatterlist.h:140 [inline] RSP: ffff88006c7cfb08
RIP: sg_init_one+0x1b3/0x240 lib/scatterlist.c:156 RSP: ffff88006c7cfb08

Fixes: 802c7f1c84e4 ("crypto: dh - Add DH software implementation")
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
crypto/dh_helper.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/crypto/dh_helper.c
+++ b/crypto/dh_helper.c
@@ -90,6 +90,14 @@ int crypto_dh_decode_key(const char *buf
params->p = (void *)(ptr + params->key_size);
params->g = (void *)(ptr + params->key_size + params->p_size);

+ /*
+ * Don't permit 'p' to be 0. It's not a prime number, and it's subject
+ * to corner cases such as 'mod 0' being undefined or
+ * crypto_kpp_maxsize() returning 0.
+ */
+ if (memchr_inv(params->p, 0, params->p_size) == NULL)
+ return -EINVAL;
+
return 0;
}
EXPORT_SYMBOL_GPL(crypto_dh_decode_key);

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