kernel.git/kernel/exit.c, branch linux-2.6.33.y

ptrace: Prepare to fix racy accesses on task breakpoints

2011-05-23T18:22:56Z

commit bf26c018490c2fce7fe9b629083b96ce0e6ad019 upstream. When a task is traced and is in a stopped state, the tracer may execute a ptrace request to examine the tracee state and get its task struct. Right after, the tracee can be killed and thus its breakpoints released. This can happen concurrently when the tracer is in the middle of reading or modifying these breakpoints, leading to dereferencing a freed pointer. Hence, to prepare the fix, create a generic breakpoint reference holding API. When a reference on the breakpoints of a task is held, the breakpoints won't be released until the last reference is dropped. After that, no more ptrace request on the task's breakpoints can be serviced for the tracer. Reported-by: Oleg Nesterov Signed-off-by: Frederic Weisbecker Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Will Deacon Cc: Prasad Cc: Paul Mundt Link: http://lkml.kernel.org/r/1302284067-7860-2-git-send-email-fweisbec@gmail.com Signed-off-by: Greg Kroah-Hartman

Fix unprotected access to task credentials in waitid()

2011-03-21T19:45:41Z

commit f362b73244fb16ea4ae127ced1467dd8adaa7733 upstream. Using a program like the following: #include #include #include #include int main() { id_t id; siginfo_t infop; pid_t res; id = fork(); if (id == 0) { sleep(1); exit(0); } kill(id, SIGSTOP); alarm(1); waitid(P_PID, id, &infop, WCONTINUED); return 0; } to call waitid() on a stopped process results in access to the child task's credentials without the RCU read lock being held - which may be replaced in the meantime - eliciting the following warning: =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/exit.c:1460 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 2 locks held by waitid02/22252: #0: (tasklist_lock){.?.?..}, at: [] do_wait+0xc5/0x310 #1: (&(&sighand->siglock)->rlock){-.-...}, at: [] wait_consider_task+0x19a/0xbe0 stack backtrace: Pid: 22252, comm: waitid02 Not tainted 2.6.35-323cd+ #3 Call Trace: [] lockdep_rcu_dereference+0xa4/0xc0 [] wait_consider_task+0xaf1/0xbe0 [] do_wait+0xf5/0x310 [] sys_waitid+0x86/0x1f0 [] ? child_wait_callback+0x0/0x70 [] system_call_fastpath+0x16/0x1b This is fixed by holding the RCU read lock in wait_task_continued() to ensure that the task's current credentials aren't destroyed between us reading the cred pointer and us reading the UID from those credentials. Furthermore, protect wait_task_stopped() in the same way. We don't need to keep holding the RCU read lock once we've read the UID from the credentials as holding the RCU read lock doesn't stop the target task from changing its creds under us - so the credentials may be outdated immediately after we've read the pointer, lock or no lock. Signed-off-by: Daniel J Blueman Signed-off-by: David Howells Acked-by: Paul E. McKenney Acked-by: Oleg Nesterov Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

posix-cpu-timers: workaround to suppress the problems with mt exec

2011-03-21T19:44:33Z

commit e0a70217107e6f9844628120412cb27bb4cea194 upstream. posix-cpu-timers.c correctly assumes that the dying process does posix_cpu_timers_exit_group() and removes all !CPUCLOCK_PERTHREAD timers from signal->cpu_timers list. But, it also assumes that timer->it.cpu.task is always the group leader, and thus the dead ->task means the dead thread group. This is obviously not true after de_thread() changes the leader. After that almost every posix_cpu_timer_ method has problems. It is not simple to fix this bug correctly. First of all, I think that timer->it.cpu should use struct pid instead of task_struct. Also, the locking should be reworked completely. In particular, tasklist_lock should not be used at all. This all needs a lot of nontrivial and hard-to-test changes. Change __exit_signal() to do posix_cpu_timers_exit_group() when the old leader dies during exec. This is not the fix, just the temporary hack to hide the problem for 2.6.37 and stable. IOW, this is obviously wrong but this is what we currently have anyway: cpu timers do not work after mt exec. In theory this change adds another race. The exiting leader can detach the timers which were attached to the new leader. However, the window between de_thread() and release_task() is small, we can pretend that sys_timer_create() was called before de_thread(). Signed-off-by: Oleg Nesterov Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

do_exit(): make sure that we run with get_fs() == USER_DS

2011-03-21T19:44:06Z

commit 33dd94ae1ccbfb7bf0fb6c692bc3d1c4269e6177 upstream. If a user manages to trigger an oops with fs set to KERNEL_DS, fs is not otherwise reset before do_exit(). do_exit may later (via mm_release in fork.c) do a put_user to a user-controlled address, potentially allowing a user to leverage an oops into a controlled write into kernel memory. This is only triggerable in the presence of another bug, but this potentially turns a lot of DoS bugs into privilege escalations, so it's worth fixing. I have proof-of-concept code which uses this bug along with CVE-2010-3849 to write a zero to an arbitrary kernel address, so I've tested that this is not theoretical. A more logical place to put this fix might be when we know an oops has occurred, before we call do_exit(), but that would involve changing every architecture, in multiple places. Let's just stick it in do_exit instead. [akpm@linux-foundation.org: update code comment] Signed-off-by: Nelson Elhage Cc: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

do_wait() optimization: do not place sub-threads on task_struct->children list

2009-12-17T23:45:31Z

Thanks to Roland who pointed out de_thread() issues. Currently we add sub-threads to ->real_parent->children list. This buys nothing but slows down do_wait(). With this patch ->children contains only main threads (group leaders). The only complication is that forget_original_parent() should iterate over sub-threads by hand, and de_thread() needs another list_replace() when it changes ->group_leader. Henceforth do_wait_thread() can never see task_detached() && !EXIT_DEAD tasks, we can remove this check (and we can unify do_wait_thread() and ptrace_do_wait()). This change can confuse the optimistic search in mm_update_next_owner(), but this is fixable and minor. Perhaps badness() and oom_kill_process() should be updated, but they should be fixed in any case. Signed-off-by: Oleg Nesterov Cc: Roland McGrath Cc: Ingo Molnar Cc: Ratan Nalumasu Cc: Vitaly Mayatskikh Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

sched: Convert pi_lock to raw_spinlock

2009-12-14T22:55:33Z

Convert locks which cannot be sleeping locks in preempt-rt to raw_spinlocks. Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra Acked-by: Ingo Molnar

tty: Move the leader test in disassociate

2009-12-11T23:18:08Z

There are two call points, both want to check that tty->signal->leader is set. Move the test into disassociate_ctty() as that will make locking changes easier in a bit Signed-off-by: Alan Cox Signed-off-by: Greg Kroah-Hartman

Merge branch 'for-2.6.33' of git://git.kernel.dk/linux-2.6-block

2009-12-08T16:19:16Z

* 'for-2.6.33' of git://git.kernel.dk/linux-2.6-block: (113 commits) cfq-iosched: Do not access cfqq after freeing it block: include linux/err.h to use ERR_PTR cfq-iosched: use call_rcu() instead of doing grace period stall on queue exit blkio: Allow CFQ group IO scheduling even when CFQ is a module blkio: Implement dynamic io controlling policy registration blkio: Export some symbols from blkio as its user CFQ can be a module block: Fix io_context leak after failure of clone with CLONE_IO block: Fix io_context leak after clone with CLONE_IO cfq-iosched: make nonrot check logic consistent io controller: quick fix for blk-cgroup and modular CFQ cfq-iosched: move IO controller declerations to a header file cfq-iosched: fix compile problem with !CONFIG_CGROUP blkio: Documentation blkio: Wait on sync-noidle queue even if rq_noidle = 1 blkio: Implement group_isolation tunable blkio: Determine async workload length based on total number of queues blkio: Wait for cfq queue to get backlogged if group is empty blkio: Propagate cgroup weight updation to cfq groups blkio: Drop the reference to queue once the task changes cgroup blkio: Provide some isolation between groups ...

Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

2009-12-05T23:30:49Z

* 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (35 commits) sched, cputime: Introduce thread_group_times() sched, cputime: Cleanups related to task_times() Revert "sched, x86: Optimize branch hint in __switch_to()" sched: Fix isolcpus boot option sched: Revert 498657a478c60be092208422fefa9c7b248729c2 sched, time: Define nsecs_to_jiffies() sched: Remove task_{u,s,g}time() sched: Introduce task_times() to replace task_{u,s}time() pair sched: Limit the number of scheduler debug messages sched.c: Call debug_show_all_locks() when dumping all tasks sched, x86: Optimize branch hint in __switch_to() sched: Optimize branch hint in context_switch() sched: Optimize branch hint in pick_next_task_fair() sched_feat_write(): Update ppos instead of file->f_pos sched: Sched_rt_periodic_timer vs cpu hotplug sched, kvm: Fix race condition involving sched_in_preempt_notifers sched: More generic WAKE_AFFINE vs select_idle_sibling() sched: Cleanup select_task_rq_fair() sched: Fix granularity of task_u/stime() sched: Fix/add missing update_rq_clock() calls ...

block: Fix io_context leak after failure of clone with CLONE_IO

2009-12-04T15:36:18Z

With CLONE_IO, parent's io_context->nr_tasks is incremented, but never decremented whenever copy_process() fails afterwards, which prevents exit_io_context() from calling IO schedulers exit functions. Give a task_struct to exit_io_context(), and call exit_io_context() instead of put_io_context() in copy_process() cleanup path. Signed-off-by: Louis Rilling Signed-off-by: Jens Axboe