Re: [PATCH] selinux: check length properly in SCTP bind hook

[Paul Moore]

On Tue, Nov 13, 2018 at 10:18 AM Ondrej Mosnacek <omosnace@xxxxxxxxxx> wrote:
>
> selinux_sctp_bind_connect() must verify if the address buffer has
> sufficient length before accessing the 'sa_family' field. See
> __sctp_connect() for a similar check.
>
> The length of the whole address ('len') is already checked in the
> callees.
>
> Reported-by: Qian Cai <cai@xxxxxx>
> Fixes: d452930fd3b9 ("selinux: Add SCTP support")
> Cc: <stable@xxxxxxxxxxxxxxx> # 4.17+
> Cc: Richard Haines <richard_c_haines@xxxxxxxxxxxxxx>
> Signed-off-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> ---
> Hi,
>
> On Mon, Nov 12, 2018 at 8:39 PM Qian Cai <cai@xxxxxx> wrote:
> > Running the trinity fuzzer on the latest mainline (rc2) generates this,
> >
> > [15029.879626] BUG: KASAN: slab-out-of-bounds in selinux_sctp_bind_connect+0x60/0x150
> > [15029.887275] Read of size 2 at addr ffff801ec53c5080 by task trinity-main/18081
> > [15029.887294]
> > [15029.887304] CPU: 28 PID: 18081 Comm: trinity-main Tainted: G        W  OE     4.20.0-rc2+ #15
> > [15029.887311] Hardware name: Huawei TaiShan 2280 /BC11SPCD, BIOS 1.50 06/01/2018
> > [15000.084786] [15029.887320] Call trace:
> > [15029.915511]  dump_backtrace+0x0/0x2c8
> > [15029.920046]  show_stack+0x24/0x30
> > [15029.923367]  dump_stack+0x118/0x19c
> > [15029.927539]  print_address_description+0x68/0x2a0
> > [15029.932245]  kasan_report+0x1b4/0x348
> > [15029.938760]  __asan_load2+0x7c/0xa0
> > [15029.945098]  selinux_sctp_bind_connect+0x60/0x150
> >
> > [15029.950571]  security_sctp_bind_connect+0x58/0x90
> > [15029.955493]  __sctp_setsockopt_connectx+0x68/0x128 [sctp]
> > [15029.960943]  sctp_setsockopt+0x764/0x2928 [sctp]
> > [15029.965564]  sock_common_setsockopt+0x6c/0x80
> > [15029.969923]  __arm64_sys_setsockopt+0x13c/0x1f0
> > [15029.974456]  el0_svc_handler+0xd4/0x198
> > [15029.978293]  el0_svc+0x8/0xc
> > [15029.981174]
> > [15029.982667] Allocated by task 18081:
> > [15029.986245]  kasan_kmalloc.part.1+0x40/0x108
> > [15029.990517]  kasan_kmalloc+0xb4/0xc8
> > [15029.994094]  __kmalloc_node+0x1c4/0x638
> > [15029.997933]  kvmalloc_node+0x98/0xa8
> > [15030.001511]  vmemdup_user+0x34/0x128
> > [15030.005137]  __sctp_setsockopt_connectx+0x44/0x128 [sctp]
> > [15030.010586]  sctp_setsockopt+0x764/0x2928 [sctp]
> > [15030.015205]  sock_common_setsockopt+0x6c/0x80
> > [15030.019564]  __arm64_sys_setsockopt+0x13c/0x1f0
> > [15030.024096]  el0_svc_handler+0xd4/0x198
> > [15030.027933]  el0_svc+0x8/0xc
> > [15030.030814]
> > [15030.032306] Freed by task 3025:
> > [15030.035451]  __kasan_slab_free+0x114/0x228
> > [15030.039548]  kasan_slab_free+0x10/0x18
> > [15030.043299]  kfree+0x114/0x408
> > [15030.046357]  selinux_sk_free_security+0x38/0x48
> > [15030.050888]  security_sk_free+0x3c/0x58
> > [15030.054727]  __sk_destruct+0x3e8/0x570
> > [15030.058478]  sk_destruct+0x4c/0x58
> > [15030.061881]  __sk_free+0x68/0x138
> > [15030.065197]  sk_free+0x3c/0x48
> > [15030.068255]  unix_release_sock+0x4a8/0x550
> > [15030.072353]  unix_release+0x34/0x50
> > [15030.075843]  __sock_release+0x74/0x110
> > [15030.079593]  sock_close+0x24/0x38
> > [15030.082913]  __fput+0x1b8/0x368
> > [15030.086055]  ____fput+0x20/0x30
> > [15030.089199]  task_work_run+0x14c/0x1a8
> > [15030.092951]  do_notify_resume+0x1e4/0x200
> > [15030.096961]  work_pending+0x8/0x14
> > [15030.100363]
> > [15030.101856] The buggy address belongs to the object at ffff801ec53c5080
> > [15030.101856]  which belongs to the cache kmalloc-128 of size 128
> > [15030.114376] The buggy address is located 0 bytes inside of
> > [15030.114376]  128-byte region [ffff801ec53c5080, ffff801ec53c5100)
> > [15030.125939] The buggy address belongs to the page:
> > [15030.130732] page:ffff7fe007b14f00 count:1 mapcount:0 mapping:ffff8016c0010480 index:0x0
> > [15030.138738] flags: 0x5fffff0000000200(slab)
> > [15030.142926] raw: 5fffff0000000200 ffff7fe007980608 ffff801ec000fd60 ffff8016c0010480
> > [15030.150671] raw: 0000000000000000 0000000000660066 00000001ffffffff 0000000000000000
> > [15030.158413] page dumped because: kasan: bad access detected
> > [15030.163984]
> > [15030.165476] Memory state around the buggy address:
> > [15030.170269]  ffff801ec53c4f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [15030.177491]  ffff801ec53c5000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [15030.184714] >ffff801ec53c5080: 01 fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [15030.191934]                    ^
> > [15030.195164]  ffff801ec53c5100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [15030.202386]  ffff801ec53c5180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > [15030.209607] ==================================================================
> > [15030.216828] Disabling lock debugging due to kernel taint
>
> I think I found the cause - Qian, can you test this patch if it fixes
> the problem?
>
>  security/selinux/hooks.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 7ce683259357..a67459eb62d5 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -5318,6 +5318,9 @@ static int selinux_sctp_bind_connect(struct sock *sk, int optname,
>         addr_buf = address;
>
>         while (walk_size < addrlen) {
> +               if (walk_size + sizeof(sa_family_t) > addrlen)
> +                       return -EINVAL;
> +
>                 addr = addr_buf;
>                 switch (addr->sa_family) {
>                 case AF_UNSPEC:

Good catch, I think you're right about this.  I'll give Qian a bit to
see if he can verify this, but as of right now I'm going to plan on
merging this into selinux/stable-4.20.

-- 
paul moore
www.paul-moore.com