general protection fault in ebitmap_destroy

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: a88cc8da0279 Merge branch 'akpm' (patches from Andrew)
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1722da4f400000
kernel config: https://syzkaller.appspot.com/x/.config?x=edf1c3031097c304
dashboard link: https://syzkaller.appspot.com/bug?extid=6664500f0f18f07a5c0e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12d43580c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+666450...@syzkaller.appspotmail.com

SELinux: failed to load policy
sel_write_load: 238 callbacks suppressed
SELinux: failed to load policy
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9316 Comm: syz-executor2 Not tainted 5.0.0-rc1+ #16
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:ebitmap_destroy+0x32/0xf0 security/selinux/ss/ebitmap.c:334
Code: 49 89 fd 41 54 53 e8 9d e6 36 fe 4d 85 ed 0f 84 99 00 00 00 e8 8f e6
36 fe 4c 89 ea 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02 00 0f
85 98 00 00 00 49 be 00 00 00 00 00 fc ff df 4d 8b
RSP: 0018:ffff88808967f5c0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff88808967f6a8 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: ffffffff834b1081 RDI: 0000000000000008
RBP: ffff88808967f5e0 R08: ffff8880972a8140 R09: ffffed1015cc5b90
R10: ffffed1015cc5b8f R11: ffff8880ae62dc7b R12: ffff888099d993c0
R13: 0000000000000008 R14: ffff888099d993c0 R15: ffff88808967f648
FS: 00007f70cd9e5700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000015e7938 CR3: 0000000096c4a000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
sens_destroy+0x49/0xa0 security/selinux/ss/policydb.c:735
sens_read+0x25d/0x460 security/selinux/ss/policydb.c:1636
policydb_read+0xed9/0x60d0 security/selinux/ss/policydb.c:2430
security_load_policy+0x423/0x1830 security/selinux/ss/services.c:2129
sel_write_load+0x25a/0x470 security/selinux/selinuxfs.c:565
__vfs_write+0x116/0xb40 fs/read_write.c:485
vfs_write+0x20c/0x580 fs/read_write.c:549
ksys_write+0x105/0x260 fs/read_write.c:598
__do_sys_write fs/read_write.c:610 [inline]
__se_sys_write fs/read_write.c:607 [inline]
__x64_sys_write+0x73/0xb0 fs/read_write.c:607
do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457ec9
Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f70cd9e4c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457ec9
RDX: 000000000000005c RSI: 0000000020000000 RDI: 0000000000000003
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f70cd9e56d4
R13: 00000000004c720f R14: 00000000004dc9a0 R15: 00000000ffffffff
Modules linked in:
---[ end trace 78ea480790940b53 ]---
RIP: 0010:ebitmap_destroy+0x32/0xf0 security/selinux/ss/ebitmap.c:334
Code: 49 89 fd 41 54 53 e8 9d e6 36 fe 4d 85 ed 0f 84 99 00 00 00 e8 8f e6
36 fe 4c 89 ea 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02 00 0f
85 98 00 00 00 49 be 00 00 00 00 00 fc ff df 4d 8b
RSP: 0018:ffff88808967f5c0 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffff88808967f6a8 RCX: dffffc0000000000
RDX: 0000000000000001 RSI: ffffffff834b1081 RDI: 0000000000000008
RBP: ffff88808967f5e0 R08: ffff8880972a8140 R09: ffffed1015cc5b90
R10: ffffed1015cc5b8f R11: ffff8880ae62dc7b R12: ffff888099d993c0
R13: 0000000000000008 R14: ffff888099d993c0 R15: ffff88808967f648
FS: 00007f70cd9e5700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000073c000 CR3: 0000000096c4a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Stephen Smalley]

Possible fix below

From cc9324299f32db326447a28a836c462fc16bc945 Mon Sep 17 00:00:00 2001
From: Stephen Smalley <s...@tycho.nsa.gov>
Date: Wed, 9 Jan 2019 10:55:10 -0500
Subject: [PATCH] selinux: fix GPF on invalid policy

levdatum->level can be NULL if we encounter an error while loading
the policy during sens_read prior to initializing it. Make sure
sens_destroy handles that case correctly.

Reported-by: syzbot+666450...@syzkaller.appspotmail.com
Signed-off-by: Stephen Smalley <s...@tycho.nsa.gov>
---
security/selinux/ss/policydb.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/selinux/ss/policydb.c b/security/selinux/ss/policydb.c
index a50d625e7946..c1c31e33657a 100644
--- a/security/selinux/ss/policydb.c
+++ b/security/selinux/ss/policydb.c
@@ -732,7 +732,8 @@ static int sens_destroy(void *key, void *datum, void *p)
kfree(key);
if (datum) {
levdatum = datum;
- ebitmap_destroy(&levdatum->level->cat);
+ if (levdatum->level)
+ ebitmap_destroy(&levdatum->level->cat);
kfree(levdatum->level);
}
kfree(datum);
--
2.20.1

[Paul Moore]

...

> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches

I'm not sure if this particular bug is one that syzbot can reproduce
(I recall a different message when it had a reproducer), but it would
be nice to get some syzbot test verification if possible when posting
(see the link above for the magic).

Regardless, this looks like a good fix to me; I'm going to merge it
into the stable-5.0 tree and assuming all goes well I'll probably send
it up to Linus early next week.

--
paul moore
www.paul-moore.com

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger
crash:

Reported-and-tested-by:
syzbot+666450...@syzkaller.appspotmail.com

Tested on:

commit: 5b0e7310a2a3 selinux: fix GPF on invalid policy
git tree:
git://git.kernel.org/pub/scm/linux/kernel/git/pcmoore/selinux.git stable-5.0
kernel config: https://syzkaller.appspot.com/x/.config?x=f4486e5876c60e6a

compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Note: testing is done by a robot and is best-effort only.