Messages in this thread Patch in this message | | | Subject | Re: WARNING in apparmor_cred_free | From | Casey Schaufler <> | Date | Fri, 11 Jan 2019 17:46:55 -0800 |
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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 >>>>> >>>>> ------------[ 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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