On 04/08/2014 12:36 PM, Steven Rostedt wrote: > On Sat, 05 Apr 2014 10:59:10 -0400 > Sasha Levin <sasha.le...@oracle.com> wrote: > >> On 07/02/2013 04:22 PM, Steven Rostedt wrote: >>> From: "Steven Rostedt (Red Hat)" <rost...@goodmis.org> >>> >>> When a trace file is opened that may access a trace array, it must >>> increment its ref count to prevent it from being deleted. >>> >>> Cc: sta...@vger.kernel.org # 3.10 >>> Reported-by: Alexander Lam <a...@google.com> >>> Signed-off-by: Steven Rostedt <rost...@goodmis.org> >> >> Hi Steven, >> >> This patch seems to cause the following lockdep warning: >> >> [ 5644.288019] ====================================================== >> [ 5644.288771] [ INFO: possible circular locking dependency detected ] >> [ 5644.289657] 3.14.0-next-20140403-sasha-00019-g7474aa9-dirty #376 Not >> tainted >> [ 5644.290568] ------------------------------------------------------- >> [ 5644.290783] trinity-c17/19105 is trying to acquire lock: >> [ 5644.290783] (trace_types_lock){+.+.+.}, at: trace_array_get >> (kernel/trace/trace.c:225) >> [ 5644.290783] >> [ 5644.290783] but task is already holding lock: >> [ 5644.290783] (&sig->cred_guard_mutex){+.+.+.}, at: prepare_bprm_creds >> (fs/exec.c:1165) >> [ 5644.290783] >> [ 5644.290783] which lock already depends on the new lock. >> [ 5644.290783] >> [ 5644.290783] >> [ 5644.290783] the existing dependency chain (in reverse order) is: >> [ 5644.290783] >> -> #2 (&sig->cred_guard_mutex){+.+.+.}: >> [ 5644.290783] lock_acquire (arch/x86/include/asm/current.h:14 >> kernel/locking/lockdep.c:3602) >> [ 5644.290783] mutex_lock_interruptible_nested (kernel/locking/mutex.c:486 >> kernel/locking/mutex.c:616) >> [ 5644.290783] proc_pid_attr_write (fs/proc/base.c:2250) >> [ 5644.290783] __kernel_write (fs/read_write.c:457) >> [ 5644.290783] write_pipe_buf (fs/splice.c:1072) >> [ 5644.290783] splice_from_pipe_feed (fs/splice.c:834) >> [ 5644.290783] __splice_from_pipe (fs/splice.c:955) >> [ 5644.290783] splice_from_pipe (fs/splice.c:990) >> [ 5644.290783] default_file_splice_write (fs/splice.c:1084) >> [ 5644.290783] SyS_splice (include/linux/fs.h:2333 fs/splice.c:1391 >> fs/splice.c:1764 fs/splice.c:1749) >> [ 5644.290783] tracesys (arch/x86/kernel/entry_64.S:749) >> [ 5644.290783] >> -> #1 (&pipe->mutex/1){+.+.+.}: >> [ 5644.290783] lock_acquire (arch/x86/include/asm/current.h:14 >> kernel/locking/lockdep.c:3602) >> [ 5644.290783] mutex_lock_nested (kernel/locking/mutex.c:486 >> kernel/locking/mutex.c:587) >> [ 5644.290783] pipe_lock_nested (fs/pipe.c:61) >> [ 5644.290783] pipe_lock (fs/pipe.c:69) >> [ 5644.290783] splice_to_pipe (include/linux/wait.h:103 fs/splice.c:247) >> [ 5644.290783] tracing_buffers_splice_read (kernel/trace/trace.c:5423) >> [ 5644.290783] do_splice_to (fs/splice.c:1151) >> [ 5644.290783] SyS_splice (fs/splice.c:1416 fs/splice.c:1764 >> fs/splice.c:1749) >> [ 5644.290783] ia32_sysret (arch/x86/ia32/ia32entry.S:430) >> [ 5644.290783] >> -> #0 (trace_types_lock){+.+.+.}: >> [ 5644.290783] __lock_acquire (kernel/locking/lockdep.c:1840 >> kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131 >> kernel/locking/lockdep.c:3182) >> [ 5644.290783] lock_acquire (arch/x86/include/asm/current.h:14 >> kernel/locking/lockdep.c:3602) >> [ 5644.290783] mutex_lock_nested (kernel/locking/mutex.c:486 >> kernel/locking/mutex.c:587) >> [ 5644.290783] trace_array_get (kernel/trace/trace.c:225) >> [ 5644.290783] tracing_open_generic_tr (kernel/trace/trace.c:3053) >> [ 5644.290783] do_dentry_open (fs/open.c:753) >> [ 5644.290783] finish_open (fs/open.c:818) >> [ 5644.290783] do_last (fs/namei.c:3040) >> [ 5644.290783] path_openat (fs/namei.c:3182) >> [ 5644.290783] do_filp_open (fs/namei.c:3231) >> [ 5644.290783] do_open_exec (fs/exec.c:766) >> [ 5644.290783] do_execve_common.isra.19 (fs/exec.c:1491) >> [ 5644.290783] compat_SyS_execve (fs/exec.c:1627) >> [ 5644.290783] ia32_ptregs_common (arch/x86/ia32/ia32entry.S:495) >> [ 5644.290783] >> [ 5644.290783] other info that might help us debug this: >> [ 5644.290783] >> [ 5644.290783] Chain exists of: >> trace_types_lock --> &pipe->mutex/1 --> &sig->cred_guard_mutex >> >> [ 5644.290783] Possible unsafe locking scenario: >> [ 5644.290783] >> [ 5644.290783] CPU0 CPU1 >> [ 5644.290783] ---- ---- >> [ 5644.290783] lock(&sig->cred_guard_mutex); >> [ 5644.290783] lock(&pipe->mutex/1); >> [ 5644.290783] lock(&sig->cred_guard_mutex); >> [ 5644.290783] lock(trace_types_lock); >> [ 5644.290783] >> [ 5644.290783] *** DEADLOCK *** >> [ 5644.290783] >> [ 5644.290783] 1 lock held by trinity-c17/19105: >> [ 5644.290783] #0: (&sig->cred_guard_mutex){+.+.+.}, at: prepare_bprm_creds >> (fs/exec.c:1165) >> [ 5644.290783] >> [ 5644.290783] stack backtrace: >> [ 5644.290783] CPU: 10 PID: 19105 Comm: trinity-c17 Not tainted >> 3.14.0-next-20140403-sasha-00019-g7474aa9-dirty #376 >> [ 5644.290783] ffffffffb4a1a1e0 ffff88071a7738f8 ffffffffb14bfb2f >> 0000000000000000 >> [ 5644.290783] ffffffffb49a9dd0 ffff88071a773948 ffffffffb14b2527 >> 0000000000000001 >> [ 5644.290783] ffff88071a7739d8 ffff88071a773948 ffff8805d98cbcf0 >> ffff8805d98cbd28 >> [ 5644.290783] Call Trace: >> [ 5644.290783] dump_stack (lib/dump_stack.c:52) >> [ 5644.290783] print_circular_bug (kernel/locking/lockdep.c:1214) >> [ 5644.290783] __lock_acquire (kernel/locking/lockdep.c:1840 >> kernel/locking/lockdep.c:1945 kernel/locking/lockdep.c:2131 >> kernel/locking/lockdep.c:3182) >> [ 5644.290783] ? _raw_spin_unlock_irqrestore >> (arch/x86/include/asm/paravirt.h:809 include/linux/spinlock_api_smp.h:160 >> kernel/locking/spinlock.c:191) >> [ 5644.290783] ? preempt_count_sub (kernel/sched/core.c:2527) >> [ 5644.290783] ? __slab_free (mm/slub.c:2598) >> [ 5644.290783] lock_acquire (arch/x86/include/asm/current.h:14 >> kernel/locking/lockdep.c:3602) >> [ 5644.290783] ? trace_array_get (kernel/trace/trace.c:225) >> [ 5644.290783] mutex_lock_nested (kernel/locking/mutex.c:486 >> kernel/locking/mutex.c:587) >> [ 5644.290783] ? trace_array_get (kernel/trace/trace.c:225) >> [ 5644.290783] ? locks_free_lock (fs/locks.c:244) >> [ 5644.290783] ? trace_array_get (kernel/trace/trace.c:225) >> [ 5644.290783] ? preempt_count_sub (kernel/sched/core.c:2527) >> [ 5644.290783] trace_array_get (kernel/trace/trace.c:225) >> [ 5644.290783] tracing_open_generic_tr (kernel/trace/trace.c:3053) >> [ 5644.290783] do_dentry_open (fs/open.c:753) >> [ 5644.290783] ? tracing_open_pipe (kernel/trace/trace.c:3047) >> [ 5644.290783] finish_open (fs/open.c:818) >> [ 5644.290783] do_last (fs/namei.c:3040) >> [ 5644.290783] ? link_path_walk (fs/namei.c:1473 fs/namei.c:1744) >> [ 5644.290783] ? __this_cpu_preempt_check (lib/smp_processor_id.c:63) >> [ 5644.290783] ? trace_hardirqs_on_caller (kernel/locking/lockdep.c:2557 >> kernel/locking/lockdep.c:2599) >> [ 5644.290783] path_openat (fs/namei.c:3182) >> [ 5644.290783] ? __lock_acquire (kernel/locking/lockdep.c:3189) >> [ 5644.290783] do_filp_open (fs/namei.c:3231) >> [ 5644.290783] ? put_lock_stats.isra.12 (arch/x86/include/asm/preempt.h:98 >> kernel/locking/lockdep.c:254) >> [ 5644.290783] ? do_execve_common.isra.19 (fs/exec.c:1489) >> [ 5644.290783] ? get_parent_ip (kernel/sched/core.c:2472) >> [ 5644.290783] do_open_exec (fs/exec.c:766) >> [ 5644.290783] do_execve_common.isra.19 (fs/exec.c:1491) >> [ 5644.290783] ? do_execve_common.isra.19 (include/linux/spinlock.h:303 >> fs/exec.c:1258 fs/exec.c:1486) >> [ 5644.290783] compat_SyS_execve (fs/exec.c:1627) >> [ 5644.290783] ia32_ptregs_common (arch/x86/ia32/ia32entry.S:495) >> > > Wait a minute! The syscall is a compat_SyS_execve, which does an > do_execve_common, which does a do_open_exec, which ends up opening a > tracing file???? > > How the hell did that happen. Is your tool execing files in the tracing > directory? I wonder if that's even possible, and if so, how can we > prevent that? The trace_pipe file (which is what uses the > tracing_open_pipe) is set to rrr. No exec should be allowed.
It could happen easily manually: # ls -al trace_pipe -r--r--r-- 1 root 0 0 Apr 8 16:43 trace_pipe # chmod 777 trace_pipe # ls -al trace_pipe -rwxrwxrwx 1 root 0 0 Apr 8 16:43 trace_pipe # ./trace_pipe Although when I mount everything for the fuzzer I do it with '-onoexec,nosuid' and the fuzzer is banned from testing mount(), so I'm not sure how it would do that thing on it's own. Thanks, Sasha -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/