public inbox for linux-crypto@vger.kernel.org
 help / color / mirror / Atom feed
* [PATCH] crypto: af_alg/hash: Fix uninit-value access in af_alg_free_sg()
@ 2023-12-11 13:59 Shigeru Yoshida
  2023-12-22  3:42 ` Herbert Xu
  0 siblings, 1 reply; 6+ messages in thread
From: Shigeru Yoshida @ 2023-12-11 13:59 UTC (permalink / raw)
  To: herbert, davem; +Cc: dhowells, linux-crypto, linux-kernel, Shigeru Yoshida

KMSAN reported the following uninit-value access issue:

=====================================================
BUG: KMSAN: uninit-value in af_alg_free_sg+0x1c1/0x270 crypto/af_alg.c:547
 af_alg_free_sg+0x1c1/0x270 crypto/af_alg.c:547
 hash_sendmsg+0x188f/0x1ce0 crypto/algif_hash.c:172
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x997/0xd60 net/socket.c:2584
 ___sys_sendmsg+0x271/0x3b0 net/socket.c:2638
 __sys_sendmsg net/socket.c:2667 [inline]
 __do_sys_sendmsg net/socket.c:2676 [inline]
 __se_sys_sendmsg net/socket.c:2674 [inline]
 __x64_sys_sendmsg+0x2fa/0x4a0 net/socket.c:2674
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

Uninit was created at:
 slab_post_alloc_hook+0x103/0x9e0 mm/slab.h:768
 slab_alloc_node mm/slub.c:3478 [inline]
 __kmem_cache_alloc_node+0x5d5/0x9b0 mm/slub.c:3517
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0x118/0x410 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 sock_kmalloc+0x104/0x1a0 net/core/sock.c:2681
 hash_accept_parent_nokey crypto/algif_hash.c:418 [inline]
 hash_accept_parent+0xbc/0x470 crypto/algif_hash.c:445
 af_alg_accept+0x1d8/0x810 crypto/af_alg.c:439
 hash_accept+0x368/0x800 crypto/algif_hash.c:254
 do_accept+0x803/0xa70 net/socket.c:1927
 __sys_accept4_file net/socket.c:1967 [inline]
 __sys_accept4+0x170/0x340 net/socket.c:1997
 __do_sys_accept4 net/socket.c:2008 [inline]
 __se_sys_accept4 net/socket.c:2005 [inline]
 __x64_sys_accept4+0xc0/0x150 net/socket.c:2005
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

CPU: 0 PID: 14168 Comm: syz-executor.2 Not tainted 6.7.0-rc4-00009-gbee0e7762ad2 #13
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-1.fc38 04/01/2014
=====================================================

In hash_sendmsg(), hash_alloc_result() may fail and return -ENOMEM if
sock_kmalloc() fails. In this case, hash_sendmsg() jumps to the unlock_free
label and calls af_alg_free_sg() with ctx->sgl.sgt.sgl uninitialized. This
causes the above uninit-value access issue for ctx->sgl.sgt.sgl.

This patch fixes this issue by initializing ctx->sgl.sgt.sgl when the
structure is allocated in hash_accept_parent_nokey().

Fixes: c662b043cdca ("crypto: af_alg/hash: Support MSG_SPLICE_PAGES")
Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
---
 crypto/algif_hash.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/crypto/algif_hash.c b/crypto/algif_hash.c
index 82c44d4899b9..a51b58d36d60 100644
--- a/crypto/algif_hash.c
+++ b/crypto/algif_hash.c
@@ -419,6 +419,7 @@ static int hash_accept_parent_nokey(void *private, struct sock *sk)
 	if (!ctx)
 		return -ENOMEM;
 
+	ctx->sgl.sgt.sgl = NULL;
 	ctx->result = NULL;
 	ctx->len = len;
 	ctx->more = false;
-- 
2.41.0


^ permalink raw reply related	[flat|nested] 6+ messages in thread
* Re: [PATCH] crypto: af_alg/hash: Fix uninit-value access in af_alg_free_sg()
@ 2024-01-03  3:05 xingwei lee
  0 siblings, 0 replies; 6+ messages in thread
From: xingwei lee @ 2024-01-03  3:05 UTC (permalink / raw)
  To: syoshida; +Cc: davem, dhowells, herbert, linux-crypto, linux-kernel

Hi,Shigeru and Herbert. Happy New Year anyway.
I also found this bug and tried to reproduce it.
My own syzkaller crashes titled "double-free in af_alg_free_sg” or
“KASAN: use-after-free in af_alg_free_sg” lead me to consider it maybe
a security-related problem.

I reproduced it with repro.c and repro.txt and also bisection to this
commit: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/crypto/algif_hash.c?id=b6d972f6898308fbe7e693bf8d44ebfdb1cd2dc4

=* repro.c =*
// autogenerated by syzkaller (https://github.com/google/syzkaller)

#define _GNU_SOURCE

#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>

uint64_t r[3] = {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffffff};

int main(void) {
 syscall(__NR_mmap, /*addr=*/0x1ffff000ul, /*len=*/0x1000ul, /*prot=*/0ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 syscall(__NR_mmap, /*addr=*/0x20000000ul, /*len=*/0x1000000ul, /*prot=*/7ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 syscall(__NR_mmap, /*addr=*/0x21000000ul, /*len=*/0x1000ul, /*prot=*/0ul,
         /*flags=*/0x32ul, /*fd=*/-1, /*offset=*/0ul);
 intptr_t res = 0;
 res = syscall(__NR_socket, /*domain=*/0x26ul, /*type=*/5ul, /*proto=*/0);
 if (res != -1) r[0] = res;
 *(uint16_t*)0x20000040 = 0x26;
 memcpy((void*)0x20000042, "hash\000\000\000\000\000\000\000\000\000\000", 14);
 *(uint32_t*)0x20000050 = 0;
 *(uint32_t*)0x20000054 = 0;
 memcpy((void*)0x20000058,
        "poly1305\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"
        "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"
        "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000"
        "\000\000\000\000\000\000\000",
        64);
 syscall(__NR_bind, /*fd=*/r[0], /*addr=*/0x20000040ul, /*addrlen=*/0x58ul);
 res = syscall(__NR_accept4, /*fd=*/r[0], /*peer=*/0ul, /*peerlen=*/0ul,
               /*flags=*/0ul);
 if (res != -1) r[1] = res;
 *(uint64_t*)0x20000d80 = 0;
 *(uint32_t*)0x20000d88 = 0;
 *(uint64_t*)0x20000d90 = 0x20000d40;
 *(uint64_t*)0x20000d40 = 0x20000d00;
 *(uint16_t*)0x20000d00 = 0;
 *(uint64_t*)0x20000d48 = 0x14;
 *(uint64_t*)0x20000d98 = 1;
 *(uint64_t*)0x20000da0 = 0;
 *(uint64_t*)0x20000da8 = 0;
 *(uint32_t*)0x20000db0 = 0;
 syscall(__NR_sendmsg, /*fd=*/r[1], /*msg=*/0x20000d80ul, /*f=*/0x400c000ul);
 res = syscall(__NR_accept4, /*fd=*/r[1], /*peer=*/0ul, /*peerlen=*/0ul,
               /*flags=*/0ul);
 if (res != -1) r[2] = res;
 *(uint64_t*)0x20000840 = 0;
 *(uint32_t*)0x20000848 = 0;
 *(uint64_t*)0x20000850 = 0;
 *(uint64_t*)0x20000858 = 0;
 *(uint64_t*)0x20000860 = 0;
 *(uint64_t*)0x20000868 = 0;
 *(uint32_t*)0x20000870 = 0x4000;
 syscall(__NR_sendmsg, /*fd=*/r[2], /*msg=*/0x20000840ul, /*f=*/0x4001ul);
 return 0;
}

=* repro.txt =*
r0 = socket$alg(0x26, 0x5, 0x0)
bind$alg(r0, &(0x7f0000000040)={0x26, 'hash\x00', 0x0, 0x0,
'poly1305\x00'}, 0x58)
r1 = accept4(r0, 0x0, 0x0, 0x0)
sendmsg$BATADV_CMD_SET_HARDIF(r1, &(0x7f0000000d80)={0x0, 0x0,
&(0x7f0000000d40)={&(0x7f0000000d00)=ANY=[@ANYBLOB, @ANYRES16=0x0,
@ANYBLOB], 0x14}}, 0x400c000)
r2 = accept4(r1, 0x0, 0x0, 0x0)
sendmsg$alg(r2, &(0x7f0000000840)={0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x4000}, 0x4001)

After analysing the uninitialized of ctx->sgl, it may cause (without
KMSAN in linux kernel)

void af_alg_free_sg(struct af_alg_sgl *sgl)
{
  int i;

  if (sgl->sgt.sgl) {
    if (sgl->need_unpin)
      for (i = 0; i < sgl->sgt.nents; i++)
        unpin_user_page(sg_page(&sgl->sgt.sgl[i]));
    if (sgl->sgt.sgl != sgl->sgl)
      kvfree(sgl->sgt.sgl);
    sgl->sgt.sgl = NULL;
  }
}

1. If sgl->sgt.sgl is 0x0, the poc triggers nothing
2. If sgl->sgt.sgl is not null but like 0xbbbbbbbbbbbbbbbb,
unpin_user_page will crash like “wild-memory access”.
3. If sgl->sgt.sgl happens to be a pointer whether it is being used or
released, sgl->sgt.nents<0, kvfree can definitely cause uaf or double
free and maybe lead to control flow hijacking.

The incorrect logic of unlock_free label can really cause security issues.

I hope the reproducer and analysis helps.

Best regards.
xingwei Lee

^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2024-01-04  2:03 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-12-11 13:59 [PATCH] crypto: af_alg/hash: Fix uninit-value access in af_alg_free_sg() Shigeru Yoshida
2023-12-22  3:42 ` Herbert Xu
2023-12-27  4:03   ` Shigeru Yoshida
2024-01-03 15:36   ` David Howells
2024-01-04  2:03     ` Herbert Xu
  -- strict thread matches above, loose matches on Subject: below --
2024-01-03  3:05 xingwei lee

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox