Messages in this thread | | | Date | Tue, 14 Aug 2012 14:16:52 -0700 | Subject | Re: yama_ptrace_access_check(): possible recursive locking detected | From | Kees Cook <> |
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On Thu, Aug 9, 2012 at 6:52 PM, Fengguang Wu <fengguang.wu@intel.com> wrote: > On Thu, Aug 09, 2012 at 06:39:34PM -0700, Kees Cook wrote: >> Hi, >> >> So, after taking a closer look at this, I cannot understand how it's >> possible. Yama's task_lock call is against "current", not "child", >> which is what ptrace_may_access() is locking. And the same code makes >> sure that current != child. Yama would never get called if current == >> child. >> >> How did you reproduce this situation? > > This warning can be triggered with Dave Jones' trinity tool: > > git://git.codemonkey.org.uk/trinity > > That's a very dangerous tool, please only run it as normal user in a > backed up and chrooted test box. I personally run it inside an initrd. > If you are interested in reproducing this, I can send you the ready > made initrd in private email.
Well, even with your initrd, I can't reproduce this. You're running this against a stock kernel? I can't see how the path you've shown can possible happen. It could only happen if "task" was "current", but there is an explicit test for that in ptrace_may_access(). Based on the traceback, this is from reading /proc/$pid/stack (or /proc/$pid/task/$tid/stack), rather than a direct ptrace() call, but the code path for task != current still stands.
I've tried both normal and "trinity -c read" and I haven't seen the trace you found. :(
If you can isolate the case further, I'm happy to fix it, but currently, I don't see a path where this can deadlock.
Thanks,
-Kees
>> On Thu, Jul 26, 2012 at 6:47 AM, Fengguang Wu <fengguang.wu@intel.com> wrote: >> > Here is a recursive lock possibility: >> > >> > ptrace_may_access() >> > => task_lock(task); >> > yama_ptrace_access_check() >> > get_task_comm() >> > => task_lock(task); >> > >> > [ 60.230444] ============================================= >> > [ 60.232078] [ INFO: possible recursive locking detected ] >> > [ 60.232078] 3.5.0+ #281 Not tainted >> > [ 60.232078] --------------------------------------------- >> > [ 60.232078] trinity-child0/17019 is trying to acquire lock: >> > [ 60.232078] (&(&p->alloc_lock)->rlock){+.+...}, at: [<c1176ffa>] get_task_comm+0x4a/0xf0 >> > [ 60.232078] >> > [ 60.232078] but task is already holding lock: >> > [ 60.232078] (&(&p->alloc_lock)->rlock){+.+...}, at: [<c10653fa>] ptrace_may_access+0x4a/0xf0 >> > [ 60.232078] >> > [ 60.232078] other info that might help us debug this: >> > [ 60.232078] Possible unsafe locking scenario: >> > [ 60.232078] >> > [ 60.232078] CPU0 >> > [ 60.232078] ---- >> > [ 60.232078] lock(&(&p->alloc_lock)->rlock); >> > [ 60.232078] lock(&(&p->alloc_lock)->rlock); >> > [ 60.232078] >> > [ 60.232078] *** DEADLOCK *** >> > [ 60.232078] >> > [ 60.232078] May be due to missing lock nesting notation >> > [ 60.232078] >> > [ 60.232078] 3 locks held by trinity-child0/17019: >> > [ 60.232078] #0: (&p->lock){+.+.+.}, at: [<c11a9683>] seq_read+0x33/0x6b0 >> > [ 60.232078] #1: (&sig->cred_guard_mutex){+.+.+.}, at: [<c11ff8ae>] lock_trace+0x2e/0xb0 >> > [ 60.232078] #2: (&(&p->alloc_lock)->rlock){+.+...}, at: [<c10653fa>] ptrace_may_access+0x4a/0xf0 >> > [ 60.232078] >> > [ 60.232078] stack backtrace: >> > [ 60.232078] Pid: 17019, comm: trinity-child0 Not tainted 3.5.0+ #281 >> > [ 60.232078] Call Trace: >> > [ 60.232078] [<c10c6238>] __lock_acquire+0x1498/0x14f0 >> > [ 60.232078] [<c10be7e7>] ? trace_hardirqs_off+0x27/0x40 >> > [ 60.232078] [<c10c6360>] lock_acquire+0xd0/0x110 >> > [ 60.232078] [<c1176ffa>] ? get_task_comm+0x4a/0xf0 >> > [ 60.232078] [<c1422290>] _raw_spin_lock+0x60/0x110 >> > [ 60.232078] [<c1176ffa>] ? get_task_comm+0x4a/0xf0 >> > [ 60.232078] [<c1176ffa>] get_task_comm+0x4a/0xf0 >> > [ 60.232078] [<c1246798>] yama_ptrace_access_check+0x468/0x4a0 >> > [ 60.232078] [<c124648f>] ? yama_ptrace_access_check+0x15f/0x4a0 >> > [ 60.232078] [<c124209a>] security_ptrace_access_check+0x1a/0x30 >> > [ 60.232078] [<c1065229>] __ptrace_may_access+0x189/0x310 >> > [ 60.232078] [<c10650cc>] ? __ptrace_may_access+0x2c/0x310 >> > [ 60.232078] [<c106542d>] ptrace_may_access+0x7d/0xf0 >> > [ 60.232078] [<c11ff8ea>] lock_trace+0x6a/0xb0 >> > [ 60.232078] [<c11ffa46>] proc_pid_stack+0x76/0x170 >> > [ 60.232078] [<c1201064>] proc_single_show+0x74/0x100 >> > [ 60.232078] [<c11a97b3>] seq_read+0x163/0x6b0 >> > [ 60.232078] [<c105bf70>] ? do_setitimer+0x220/0x330 >> > [ 60.232078] [<c11a9650>] ? seq_lseek+0x1f0/0x1f0 >> > [ 60.232078] [<c116b55a>] vfs_read+0xca/0x280 >> > [ 60.232078] [<c11a9650>] ? seq_lseek+0x1f0/0x1f0 >> > [ 60.232078] [<c116b776>] sys_read+0x66/0xe0 >> > [ 60.232078] [<c1423d9d>] syscall_call+0x7/0xb >> > [ 60.232078] [<c1420000>] ? __schedule+0x2a0/0xc80
-- Kees Cook Chrome OS Security
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