Messages in this thread | | | From | Dmitry Vyukov <> | Date | Mon, 14 Jan 2019 12:12:11 +0100 | Subject | Re: WARNING in apparmor_cred_free |
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On Sat, Jan 12, 2019 at 2:47 AM Casey Schaufler <casey@schaufler-ca.com> wrote: > > On 1/11/2019 3:20 PM, Casey Schaufler wrote: > > On 1/11/2019 2:43 PM, Casey Schaufler wrote: > >> On 1/11/2019 2:30 PM, John Johansen wrote: > >>> On 1/11/19 2:11 PM, Casey Schaufler wrote: > >>>> On 1/11/2019 1:43 AM, syzbot wrote: > >>>>> Hello, > >>>>> > >>>>> syzbot found the following crash on: > >>>>> > >>>>> HEAD commit: b808822a75a3 Add linux-next specific files for 20190111 > >>>>> git tree: linux-next > >>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=179c22f7400000 > >>>>> kernel config: https://syzkaller.appspot.com/x/.config?x=c052ead0aed5001b > >>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=69ca07954461f189e808 > >>>>> compiler: gcc (GCC) 9.0.0 20181231 (experimental) > >>>>> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=162d947f400000 > >>>>> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=139f6c37400000 > >>>>> > >>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit: > >>>>> Reported-by: syzbot+69ca07954461f189e808@syzkaller.appspotmail.com
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Please include the tag for tracking purposes.
> >>>>> ------------[ cut here ]------------ > >>>>> AppArmor WARN cred_label: ((!blob)): > >>>>> WARNING: CPU: 0 PID: 0 at security/apparmor/include/cred.h:30 cred_label security/apparmor/include/cred.h:30 [inline] > >>>>> WARNING: CPU: 0 PID: 0 at security/apparmor/include/cred.h:30 apparmor_cred_free+0x12f/0x1a0 security/apparmor/lsm.c:62 > >>>>> Kernel panic - not syncing: panic_on_warn set ... > >>>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.0.0-rc1-next-20190111 #10 > >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > >>>>> Call Trace: > >>>>> <IRQ> > >>>>> __dump_stack lib/dump_stack.c:77 [inline] > >>>>> dump_stack+0x1db/0x2d0 lib/dump_stack.c:113 > >>>>> panic+0x2cb/0x65c kernel/panic.c:214 > >>>>> __warn.cold+0x20/0x48 kernel/panic.c:571 > >>>>> report_bug+0x263/0x2b0 lib/bug.c:186 > >>>>> fixup_bug arch/x86/kernel/traps.c:178 [inline] > >>>>> fixup_bug arch/x86/kernel/traps.c:173 [inline] > >>>>> do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271 > >>>>> do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:290 > >>>>> invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:973 > >>>>> RIP: 0010:cred_label security/apparmor/include/cred.h:30 [inline] > >>>>> RIP: 0010:apparmor_cred_free+0x12f/0x1a0 security/apparmor/lsm.c:62 > >>>>> Code: 7c 88 48 c7 c7 00 d0 7c 88 e8 fd 70 f2 fd 0f 0b eb a9 e8 54 3f 29 fe 48 c7 c6 c0 df 7c 88 48 c7 c7 00 d0 7c 88 e8 e1 70 f2 fd <0f> 0b 48 b8 00 00 00 00 00 fc ff df 80 38 00 75 4a 4c 8b 2c 25 00 > >>>>> RSP: 0018:ffff8880ae6079f8 EFLAGS: 00010286 > >>>>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > >>>>> RDX: 0000000000000100 RSI: ffffffff81687fa6 RDI: 0000000000000006 > >>>>> RBP: ffff8880ae607a18 R08: ffffffff8987dec0 R09: 0000000000000000 > >>>>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880a86b3100 > >>>>> R13: ffff8880a86b3100 R14: ffff8880a86b3188 R15: dffffc0000000000 > >>>>> security_cred_free+0x4b/0xf0 security/security.c:1490 > >>>> The obvious thing to do is put a check in security_cred_free > >>>> for a NULL cred->security, in which case the LSM hooks > >>>> wouldn't get called. > >>> Right, but the question is should we? To my thinking we shouldn't > >>> ever have a cred without cred->security, unless the cred was > >>> allocated but a later step in its construction, say allocating > >>> ->security failed. > >> If allocating ->security fails in security_cred_alloc_blank() > >> or security_prepare_creds() you don't have to do anything but > >> fail because the LSM hooks are not called before the allocation. > >> > >>> In which case I'd rather see the cred directly freed and not > >>> call into security_cred_free() as I like being able to detect > >>> corrupt creds. > >> I think we need to look for some bit of code that's setting > >> cred->security to NULL inappropriately. > > If security_cred_alloc_blank() fails for lack of memory > > in cred_alloc_blank() abort_creds() will be called. This > > in turn calls put_cred() and put_cred_rcu(), which will > > call security_cred_free() with ->security set to NULL. > > > > put_cred_rcu() is the only caller of security_cred_free(). > > The ->security == NULL check can be in either put_cred_rcu() > > or in security_cred_free(). I suggest the latter as the > > cleanest option. > > From 47134986133c822e1d88860fa2b108f92c97a7ff Mon Sep 17 00:00:00 2001 > From: Casey Schaufler <casey@schaufler-ca.com> > Date: Fri, 11 Jan 2019 17:31:50 -0800 > Subject: [PATCH 1/2] LSM: Check for NULL cred-security on free > > Check that the cred security blob has been set before trying > to clean it up. There is a case during credential initialization > that could result in this. > > Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> > --- > security/security.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/security/security.c b/security/security.c > index a618e22df5c6..7bffc86d4e87 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -1477,6 +1477,13 @@ int security_cred_alloc_blank(struct cred *cred, gfp_t gfp) > > void security_cred_free(struct cred *cred) > { > + /* > + * There is a failure case in prepare_creds() that > + * may result in a call here with ->security being NULL. > + */ > + if (unlikely(cred->security == NULL)) > + return; > + > call_void_hook(cred_free, cred); > > kfree(cred->security); > -- > 2.20.1 > >
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