linux/kernel/fork.c, branch v5.4

fork: fix pidfd_poll()'s return type

2019-11-20T10:48:50Z

pidfd_poll() is defined as returning 'unsigned int' but the .poll method is declared as returning '__poll_t', a bitwise type. Fix this by using the proper return type and using the EPOLL constants instead of the POLL ones, as required for __poll_t. Fixes: b53b0b9d9a61 ("pidfd: add polling support") Cc: Joel Fernandes (Google) Cc: stable@vger.kernel.org # 5.3 Signed-off-by: Luc Van Oostenryck Reviewed-by: Christian Brauner Link: https://lore.kernel.org/r/20191120003320.31138-1-luc.vanoostenryck@gmail.com Signed-off-by: Christian Brauner

clone3: validate stack arguments

2019-11-05T14:50:14Z

Validate the stack arguments and setup the stack depening on whether or not it is growing down or up. Legacy clone() required userspace to know in which direction the stack is growing and pass down the stack pointer appropriately. To make things more confusing microblaze uses a variant of the clone() syscall selected by CONFIG_CLONE_BACKWARDS3 that takes an additional stack_size argument. IA64 has a separate clone2() syscall which also takes an additional stack_size argument. Finally, parisc has a stack that is growing upwards. Userspace therefore has a lot nasty code like the following: #define __STACK_SIZE (8 * 1024 * 1024) pid_t sys_clone(int (*fn)(void *), void *arg, int flags, int *pidfd) { pid_t ret; void *stack; stack = malloc(__STACK_SIZE); if (!stack) return -ENOMEM; #ifdef __ia64__ ret = __clone2(fn, stack, __STACK_SIZE, flags | SIGCHLD, arg, pidfd); #elif defined(__parisc__) /* stack grows up */ ret = clone(fn, stack, flags | SIGCHLD, arg, pidfd); #else ret = clone(fn, stack + __STACK_SIZE, flags | SIGCHLD, arg, pidfd); #endif return ret; } or even crazier variants such as [3]. With clone3() we have the ability to validate the stack. We can check that when stack_size is passed, the stack pointer is valid and the other way around. We can also check that the memory area userspace gave us is fine to use via access_ok(). Furthermore, we probably should not require userspace to know in which direction the stack is growing. It is easy for us to do this in the kernel and I couldn't find the original reasoning behind exposing this detail to userspace. /* Intentional user visible API change */ clone3() was released with 5.3. Currently, it is not documented and very unclear to userspace how the stack and stack_size argument have to be passed. After talking to glibc folks we concluded that trying to change clone3() to setup the stack instead of requiring userspace to do this is the right course of action. Note, that this is an explicit change in user visible behavior we introduce with this patch. If it breaks someone's use-case we will revert! (And then e.g. place the new behavior under an appropriate flag.) Breaking someone's use-case is very unlikely though. First, neither glibc nor musl currently expose a wrapper for clone3(). Second, there is no real motivation for anyone to use clone3() directly since it does not provide features that legacy clone doesn't. New features for clone3() will first happen in v5.5 which is why v5.4 is still a good time to try and make that change now and backport it to v5.3. Searches on [4] did not reveal any packages calling clone3(). [1]: https://lore.kernel.org/r/CAG48ez3q=BeNcuVTKBN79kJui4vC6nw0Bfq6xc-i0neheT17TA@mail.gmail.com [2]: https://lore.kernel.org/r/20191028172143.4vnnjpdljfnexaq5@wittgenstein [3]: https://github.com/systemd/systemd/blob/5238e9575906297608ff802a27e2ff9effa3b338/src/basic/raw-clone.h#L31 [4]: https://codesearch.debian.net Fixes: 7f192e3cd316 ("fork: add clone3") Cc: Kees Cook Cc: Jann Horn Cc: David Howells Cc: Ingo Molnar Cc: Oleg Nesterov Cc: Linus Torvalds Cc: Florian Weimer Cc: Peter Zijlstra Cc: linux-api@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: # 5.3 Cc: GNU C Library Signed-off-by: Christian Brauner Acked-by: Arnd Bergmann Acked-by: Aleksa Sarai Link: https://lore.kernel.org/r/20191031113608.20713-1-christian.brauner@ubuntu.com

kernel/sysctl.c: do not override max_threads provided by userspace

2019-10-07T22:47:19Z

Partially revert 16db3d3f1170 ("kernel/sysctl.c: threads-max observe limits") because the patch is causing a regression to any workload which needs to override the auto-tuning of the limit provided by kernel. set_max_threads is implementing a boot time guesstimate to provide a sensible limit of the concurrently running threads so that runaways will not deplete all the memory. This is a good thing in general but there are workloads which might need to increase this limit for an application to run (reportedly WebSpher MQ is affected) and that is simply not possible after the mentioned change. It is also very dubious to override an admin decision by an estimation that doesn't have any direct relation to correctness of the kernel operation. Fix this by dropping set_max_threads from sysctl_max_threads so any value is accepted as long as it fits into MAX_THREADS which is important to check because allowing more threads could break internal robust futex restriction. While at it, do not use MIN_THREADS as the lower boundary because it is also only a heuristic for automatic estimation and admin might have a good reason to stop new threads to be created even when below this limit. This became more severe when we switched x86 from 4k to 8k kernel stacks. Starting since 6538b8ea886e ("x86_64: expand kernel stack to 16K") (3.16) we use THREAD_SIZE_ORDER = 2 and that halved the auto-tuned value. In the particular case 3.12 kernel.threads-max = 515561 4.4 kernel.threads-max = 200000 Neither of the two values is really insane on 32GB machine. I am not sure we want/need to tune the max_thread value further. If anything the tuning should be removed altogether if proven not useful in general. But we definitely need a way to override this auto-tuning. Link: http://lkml.kernel.org/r/20190922065801.GB18814@dhcp22.suse.cz Fixes: 16db3d3f1170 ("kernel/sysctl.c: threads-max observe limits") Signed-off-by: Michal Hocko Reviewed-by: "Eric W. Biederman" Cc: Heinrich Schuchardt Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'copy-struct-from-user-v5.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux

2019-10-04T17:36:31Z

Pull copy_struct_from_user() helper from Christian Brauner: "This contains the copy_struct_from_user() helper which got split out from the openat2() patchset. It is a generic interface designed to copy a struct from userspace. The helper will be especially useful for structs versioned by size of which we have quite a few. This allows for backwards compatibility, i.e. an extended struct can be passed to an older kernel, or a legacy struct can be passed to a newer kernel. For the first case (extended struct, older kernel) the new fields in an extended struct can be set to zero and the struct safely passed to an older kernel. The most obvious benefit is that this helper lets us get rid of duplicate code present in at least sched_setattr(), perf_event_open(), and clone3(). More importantly it will also help to ensure that users implementing versioning-by-size end up with the same core semantics. This point is especially crucial since we have at least one case where versioning-by-size is used but with slighly different semantics: sched_setattr(), perf_event_open(), and clone3() all do do similar checks to copy_struct_from_user() while rt_sigprocmask(2) always rejects differently-sized struct arguments. With this pull request we also switch over sched_setattr(), perf_event_open(), and clone3() to use the new helper" * tag 'copy-struct-from-user-v5.4-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/brauner/linux: usercopy: Add parentheses around assignment in test_copy_struct_from_user perf_event_open: switch to copy_struct_from_user() sched_setattr: switch to copy_struct_from_user() clone3: switch to copy_struct_from_user() lib: introduce copy_struct_from_user() helper

fork: add kernel-doc for clone3

2019-10-03T19:18:06Z

Add kernel-doc for the clone3() syscall. Link: https://lore.kernel.org/r/20191001114701.24661-2-christian.brauner@ubuntu.com Signed-off-by: Christian Brauner

clone3: switch to copy_struct_from_user()

2019-10-01T13:45:10Z

Switch clone3() syscall from it's own copying struct clone_args from userspace to the new dedicated copy_struct_from_user() helper. The change is very straightforward, and helps unify the syscall interface for struct-from-userspace syscalls. Additionally, explicitly define CLONE_ARGS_SIZE_VER0 to match the other users of the struct-extension pattern. Signed-off-by: Aleksa Sarai Reviewed-by: Kees Cook Reviewed-by: Christian Brauner [christian.brauner@ubuntu.com: improve commit message] Link: https://lore.kernel.org/r/20191001011055.19283-3-cyphar@cyphar.com Signed-off-by: Christian Brauner

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

2019-09-28T19:39:07Z

Pull scheduler fixes from Ingo Molnar: - Apply a number of membarrier related fixes and cleanups, which fixes a use-after-free race in the membarrier code - Introduce proper RCU protection for tasks on the runqueue - to get rid of the subtle task_rcu_dereference() interface that was easy to get wrong - Misc fixes, but also an EAS speedup * 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/fair: Avoid redundant EAS calculation sched/core: Remove double update_max_interval() call on CPU startup sched/core: Fix preempt_schedule() interrupt return comment sched/fair: Fix -Wunused-but-set-variable warnings sched/core: Fix migration to invalid CPU in __set_cpus_allowed_ptr() sched/membarrier: Return -ENOMEM to userspace on memory allocation failure sched/membarrier: Skip IPIs when mm->mm_users == 1 selftests, sched/membarrier: Add multi-threaded test sched/membarrier: Fix p->mm->membarrier_state racy load sched/membarrier: Call sync_core only before usermode for same mm sched/membarrier: Remove redundant check sched/membarrier: Fix private expedited registration check tasks, sched/core: RCUify the assignment of rq->curr tasks, sched/core: With a grace period after finish_task_switch(), remove unnecessary code tasks, sched/core: Ensure tasks are available for a grace period after leaving the runqueue tasks: Add a count of task RCU users sched/core: Convert vcpu_is_preempted() from macro to an inline function sched/fair: Remove unused cfs_rq_clock_task() function

fork: improve error message for corrupted page tables

2019-09-26T00:51:40Z

When a user process exits, the kernel cleans up the mm_struct of the user process and during cleanup, check_mm() checks the page tables of the user process for corruption (E.g: unexpected page flags set/cleared). For corrupted page tables, the error message printed by check_mm() isn't very clear as it prints the loop index instead of page table type (E.g: Resident file mapping pages vs Resident shared memory pages). The loop index in check_mm() is used to index rss_stat[] which represents individual memory type stats. Hence, instead of printing index, print memory type, thereby improving error message. Without patch: -------------- [ 204.836425] mm/pgtable-generic.c:29: bad p4d 0000000089eb4e92(800000025f941467) [ 204.836544] BUG: Bad rss-counter state mm:00000000f75895ea idx:0 val:2 [ 204.836615] BUG: Bad rss-counter state mm:00000000f75895ea idx:1 val:5 [ 204.836685] BUG: non-zero pgtables_bytes on freeing mm: 20480 With patch: ----------- [ 69.815453] mm/pgtable-generic.c:29: bad p4d 0000000084653642(800000025ca37467) [ 69.815872] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_FILEPAGES val:2 [ 69.815962] BUG: Bad rss-counter state mm:00000000014a6c03 type:MM_ANONPAGES val:5 [ 69.816050] BUG: non-zero pgtables_bytes on freeing mm: 20480 Also, change print function (from printk(KERN_ALERT, ..) to pr_alert()) so that it matches the other print statement. Link: http://lkml.kernel.org/r/da75b5153f617f4c5739c08ee6ebeb3d19db0fbc.1565123758.git.sai.praneeth.prakhya@intel.com Signed-off-by: Sai Praneeth Prakhya Reviewed-by: Anshuman Khandual Suggested-by: Dave Hansen Acked-by: Michal Hocko Acked-by: Vlastimil Babka Acked-by: Dave Hansen Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

tasks, sched/core: Ensure tasks are available for a grace period after leaving the runqueue

2019-09-25T15:42:29Z

In the ordinary case today the RCU grace period for a task_struct is triggered when another process wait's for it's zombine and causes the kernel to call release_task(). As the waiting task has to receive a signal and then act upon it before this happens, typically this will occur after the original task as been removed from the runqueue. Unfortunaty in some cases such as self reaping tasks it can be shown that release_task() will be called starting the grace period for task_struct long before the task leaves the runqueue. Therefore use put_task_struct_rcu_user() in finish_task_switch() to guarantee that the there is a RCU lifetime after the task leaves the runqueue. Besides the change in the start of the RCU grace period for the task_struct this change may cause perf_event_delayed_put and trace_sched_process_free. The function perf_event_delayed_put boils down to just a WARN_ON for cases that I assume never show happen. So I don't see any problem with delaying it. The function trace_sched_process_free is a trace point and thus visible to user space. Occassionally userspace has the strangest dependencies so this has a miniscule chance of causing a regression. This change only changes the timing of when the tracepoint is called. The change in timing arguably gives userspace a more accurate picture of what is going on. So I don't expect there to be a regression. In the case where a task self reaps we are pretty much guaranteed that the RCU grace period is delayed. So we should get quite a bit of coverage in of this worst case for the change in a normal threaded workload. So I expect any issues to turn up quickly or not at all. I have lightly tested this change and everything appears to work fine. Inspired-by: Linus Torvalds Inspired-by: Oleg Nesterov Signed-off-by: Eric W. Biederman Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Metcalf Cc: Christoph Lameter Cc: Davidlohr Bueso Cc: Kirill Tkhai Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Russell King - ARM Linux admin Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/87r24jdpl5.fsf_-_@x220.int.ebiederm.org Signed-off-by: Ingo Molnar

tasks: Add a count of task RCU users

2019-09-25T15:42:29Z

Add a count of the number of RCU users (currently 1) of the task struct so that we can later add the scheduler case and get rid of the very subtle task_rcu_dereference(), and just use rcu_dereference(). As suggested by Oleg have the count overlap rcu_head so that no additional space in task_struct is required. Inspired-by: Linus Torvalds Inspired-by: Oleg Nesterov Signed-off-by: Eric W. Biederman Signed-off-by: Peter Zijlstra (Intel) Cc: Chris Metcalf Cc: Christoph Lameter Cc: Davidlohr Bueso Cc: Kirill Tkhai Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Russell King - ARM Linux admin Cc: Thomas Gleixner Link: https://lkml.kernel.org/r/87woebdplt.fsf_-_@x220.int.ebiederm.org Signed-off-by: Ingo Molnar