On Sat, Jul 3, 2021 at 6:16 PM Casey Schaufler [off-list ref] wrote:

On 7/2/2021 10:51 PM, Dmitry Vyukov wrote:

quoted

On Sat, Jul 3, 2021 at 7:41 AM syzbot
[off-list ref] wrote:

quoted

Hello,

syzbot found the following issue on:

HEAD commit:    62fb9874 Linux 5.13
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12ffa118300000
kernel config:  https://syzkaller.appspot.com/x/.config?x=19404adbea015a58
dashboard link: https://syzkaller.appspot.com/bug?extid=d1e3b1d92d25abf97943
compiler:       Debian clang version 11.0.1-2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d1e3b1d92d25abf97943@syzkaller.appspotmail.com

+Casey for what looks like a smackfs issue

This is from the new mount infrastructure introduced by
David Howells in November 2018. It makes sense that there
may be a problem in SELinux as well, as the code was introduced
by the same developer at the same time for the same purpose.

quoted

The crash was triggered by this test case:

21:55:33 executing program 1:
r0 = fsopen(&(0x7f0000000040)='ext3\x00', 0x1)
fsconfig$FSCONFIG_SET_STRING(r0, 0x1, &(0x7f00000002c0)='smackfsroot',
&(0x7f0000000300)='default_permissions', 0x0)

And I think the issue is in smack_fs_context_parse_param():
https://elixir.bootlin.com/linux/latest/source/security/smack/smack_lsm.c#L691

But it seems that selinux_fs_context_parse_param() contains the same issue:
https://elixir.bootlin.com/linux/latest/source/security/selinux/hooks.c#L2919
+So selinux maintainers as well.

quoted

general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
CPU: 0 PID: 20300 Comm: syz-executor.1 Not tainted 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:memchr+0x2f/0x70 lib/string.c:1054
Code: 41 54 53 48 89 d3 41 89 f7 45 31 f6 49 bc 00 00 00 00 00 fc ff df 0f 1f 44 00 00 48 85 db 74 3b 48 89 fd 48 89 f8 48 c1 e8 03 <42> 0f b6 04 20 84 c0 75 0f 48 ff cb 48 8d 7d 01 44 38 7d 00 75 db
RSP: 0018:ffffc90001dafd00 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000013 RCX: dffffc0000000000
RDX: 0000000000000013 RSI: 000000000000002c RDI: 0000000000000000
RBP: 0000000000000000 R08: ffffffff81e171bf R09: ffffffff81e16f95
R10: 0000000000000002 R11: ffff88807e96b880 R12: dffffc0000000000
R13: ffff888020894000 R14: 0000000000000000 R15: 000000000000002c
FS:  00007fe01ae27700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005645a8 CR3: 0000000018afc000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 legacy_parse_param+0x461/0x7e0 fs/fs_context.c:537
 vfs_parse_fs_param+0x1e5/0x460 fs/fs_context.c:117

It's Sunday morning and perhaps my mind is not yet in a "hey, let's
look at VFS kernel code!" mindset, but I'm not convinced the problem
is the 'param->string = NULL' assignment in the LSM hooks.  In both
the case of SELinux and Smack that code ends up returning either a 0
(Smack) or a 1 (SELinux) - that's a little odd in it's own way, but I
don't believe it is relevant here - either way these return values are
not equal to -ENOPARAM so we should end up returning early from
vfs_parse_fs_param before it calls down into legacy_parse_param():

Taken from https://elixir.bootlin.com/linux/latest/source/fs/fs_context.c#L109 :

  ret = security_fs_context_parse_param(fc, param);
  if (ret != -ENOPARAM)
    /* Param belongs to the LSM or is disallowed by the LSM; so
     * don't pass to the FS.
     */
    return ret;

  if (fc->ops->parse_param) {
    ret = fc->ops->parse_param(fc, param);
    if (ret != -ENOPARAM)
      return ret;
  }

quoted

quoted

 vfs_fsconfig_locked fs/fsopen.c:265 [inline]
 __do_sys_fsconfig fs/fsopen.c:439 [inline]
 __se_sys_fsconfig+0xba9/0xff0 fs/fsopen.c:314
 do_syscall_64+0x3f/0xb0 arch/x86/entry/common.c:47
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x4665d9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe01ae27188 EFLAGS: 00000246 ORIG_RAX: 00000000000001af
RAX: ffffffffffffffda RBX: 000000000056bf80 RCX: 00000000004665d9
RDX: 00000000200002c0 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 00000000004bfcb9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020000300 R11: 0000000000000246 R12: 000000000056bf80
R13: 00007ffd4bb7c5bf R14: 00007fe01ae27300 R15: 0000000000022000
Modules linked in:
---[ end trace 5d7119165725bd63 ]---

-- 
paul moore
www.paul-moore.com