user/sven/linux.git/kernel/fork.c, branch v4.19.59

userfaultfd: use RCU to free the task struct when fork fails

2019-05-22T05:37:41Z

commit c3f3ce049f7d97cc7ec9c01cb51d9ec74e0f37c2 upstream. The task structure is freed while get_mem_cgroup_from_mm() holds rcu_read_lock() and dereferences mm->owner. get_mem_cgroup_from_mm() failing fork() ---- --- task = mm->owner mm->owner = NULL; free(task) if (task) *task; /* use after free */ The fix consists in freeing the task with RCU also in the fork failure case, exactly like it always happens for the regular exit(2) path. That is enough to make the rcu_read_lock hold in get_mem_cgroup_from_mm() (left side above) effective to avoid a use after free when dereferencing the task structure. An alternate possible fix would be to defer the delivery of the userfaultfd contexts to the monitor until after fork() is guaranteed to succeed. Such a change would require more changes because it would create a strict ordering dependency where the uffd methods would need to be called beyond the last potentially failing branch in order to be safe. This solution as opposed only adds the dependency to common code to set mm->owner to NULL and to free the task struct that was pointed by mm->owner with RCU, if fork ends up failing. The userfaultfd methods can still be called anywhere during the fork runtime and the monitor will keep discarding orphaned "mm" coming from failed forks in userland. This race condition couldn't trigger if CONFIG_MEMCG was set =n at build time. [aarcange@redhat.com: improve changelog, reduce #ifdefs per Michal] Link: http://lkml.kernel.org/r/20190429035752.4508-1-aarcange@redhat.com Link: http://lkml.kernel.org/r/20190325225636.11635-2-aarcange@redhat.com Fixes: 893e26e61d04 ("userfaultfd: non-cooperative: Add fork() event") Signed-off-by: Andrea Arcangeli Tested-by: zhong jiang Reported-by: syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com Cc: Oleg Nesterov Cc: Jann Horn Cc: Hugh Dickins Cc: Mike Rapoport Cc: Mike Kravetz Cc: Peter Xu Cc: Jason Gunthorpe Cc: "Kirill A . Shutemov" Cc: Michal Hocko Cc: zhong jiang Cc: syzbot+cbb52e396df3e565ab02@syzkaller.appspotmail.com Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

fork: record start_time late

2019-01-13T08:51:04Z

commit 7b55851367136b1efd84d98fea81ba57a98304cf upstream. This changes the fork(2) syscall to record the process start_time after initializing the basic task structure but still before making the new process visible to user-space. Technically, we could record the start_time anytime during fork(2). But this might lead to scenarios where a start_time is recorded long before a process becomes visible to user-space. For instance, with userfaultfd(2) and TLS, user-space can delay the execution of fork(2) for an indefinite amount of time (and will, if this causes network access, or similar). By recording the start_time late, it much closer reflects the point in time where the process becomes live and can be observed by other processes. Lastly, this makes it much harder for user-space to predict and control the start_time they get assigned. Previously, user-space could fork a process and stall it in copy_thread_tls() before its pid is allocated, but after its start_time is recorded. This can be misused to later-on cycle through PIDs and resume the stalled fork(2) yielding a process that has the same pid and start_time as a process that existed before. This can be used to circumvent security systems that identify processes by their pid+start_time combination. Even though user-space was always aware that start_time recording is flaky (but several projects are known to still rely on start_time-based identification), changing the start_time to be recorded late will help mitigate existing attacks and make it much harder for user-space to control the start_time a process gets assigned. Reported-by: Jann Horn Signed-off-by: Tom Gundersen Signed-off-by: David Herrmann Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mm: respect arch_dup_mmap() return value

2018-09-04T23:45:02Z

Commit d70f2a14b72a ("include/linux/sched/mm.h: uninline mmdrop_async(), etc") ignored the return value of arch_dup_mmap(). As a result, on x86, a failure to duplicate the LDT (e.g. due to memory allocation error) would leave the duplicated memory mapping in an inconsistent state. Fix by using the return value, as it was before the change. Link: http://lkml.kernel.org/r/20180823051229.211856-1-namit@vmware.com Fixes: d70f2a14b72a4 ("include/linux/sched/mm.h: uninline mmdrop_async(), etc") Signed-off-by: Nadav Amit Acked-by: Michal Hocko Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'akpm' (patches from Andrew)

2018-08-22T19:34:08Z

Merge more updates from Andrew Morton: - the rest of MM - procfs updates - various misc things - more y2038 fixes - get_maintainer updates - lib/ updates - checkpatch updates - various epoll updates - autofs updates - hfsplus - some reiserfs work - fatfs updates - signal.c cleanups - ipc/ updates * emailed patches from Andrew Morton : (166 commits) ipc/util.c: update return value of ipc_getref from int to bool ipc/util.c: further variable name cleanups ipc: simplify ipc initialization ipc: get rid of ids->tables_initialized hack lib/rhashtable: guarantee initial hashtable allocation lib/rhashtable: simplify bucket_table_alloc() ipc: drop ipc_lock() ipc/util.c: correct comment in ipc_obtain_object_check ipc: rename ipcctl_pre_down_nolock() ipc/util.c: use ipc_rcu_putref() for failues in ipc_addid() ipc: reorganize initialization of kern_ipc_perm.seq ipc: compute kern_ipc_perm.id under the ipc lock init/Kconfig: remove EXPERT from CHECKPOINT_RESTORE fs/sysv/inode.c: use ktime_get_real_seconds() for superblock stamp adfs: use timespec64 for time conversion kernel/sysctl.c: fix typos in comments drivers/rapidio/devices/rio_mport_cdev.c: remove redundant pointer md fork: don't copy inconsistent signal handler state to child signal: make get_signal() return bool signal: make sigkill_pending() return bool ...

fork: don't copy inconsistent signal handler state to child

2018-08-22T17:52:51Z

Before this change, if a multithreaded process forks while one of its threads is changing a signal handler using sigaction(), the memcpy() in copy_sighand() can race with the struct assignment in do_sigaction(). It isn't clear whether this can cause corruption of the userspace signal handler pointer, but it definitely can cause inconsistency between different fields of struct sigaction. Take the appropriate spinlock to avoid this. I have tested that this patch prevents inconsistency between sa_sigaction and sa_flags, which is possible before this patch. Link: http://lkml.kernel.org/r/20180702145108.73189-1-jannh@google.com Signed-off-by: Jann Horn Acked-by: Michal Hocko Reviewed-by: Andrew Morton Cc: Rik van Riel Cc: "Peter Zijlstra (Intel)" Cc: Kees Cook Cc: Oleg Nesterov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kernel/hung_task.c: allow to set checking interval separately from timeout

2018-08-22T17:52:47Z

Currently task hung checking interval is equal to timeout, as the result hung is detected anywhere between timeout and 2*timeout. This is fine for most interactive environments, but this hurts automated testing setups (syzbot). In an automated setup we need to strictly order CPU lockup < RCU stall < workqueue lockup < task hung < silent loss, so that RCU stall is not detected as task hung and task hung is not detected as silent machine loss. The large variance in task hung detection timeout requires setting silent machine loss timeout to a very large value (e.g. if task hung is 3 mins, then silent loss need to be set to ~7 mins). The additional 3 minutes significantly reduce testing efficiency because usually we crash kernel within a minute, and this can add hours to bug localization process as it needs to do dozens of tests. Allow setting checking interval separately from timeout. This allows to set timeout to, say, 3 minutes, but checking interval to 10 secs. The interval is controlled via a new hung_task_check_interval_secs sysctl, similar to the existing hung_task_timeout_secs sysctl. The default value of 0 results in the current behavior: checking interval is equal to timeout. [akpm@linux-foundation.org: update hung_task_timeout_max's comment] Link: http://lkml.kernel.org/r/20180611111004.203513-1-dvyukov@google.com Signed-off-by: Dmitry Vyukov Cc: Paul E. McKenney Cc: Tetsuo Handa Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: zero out the vma in vma_init()

2018-08-22T17:52:44Z

Rather than in vm_area_alloc(). To ensure that the various oddball stack-based vmas are in a good state. Some of the callers were zeroing them out, others were not. Acked-by: Kirill A. Shutemov Cc: Russell King Cc: Dmitry Vyukov Cc: Oleg Nesterov Cc: Andrea Arcangeli Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge branch 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2018-08-21T20:47:29Z

Pull core signal handling updates from Eric Biederman: "It was observed that a periodic timer in combination with a sufficiently expensive fork could prevent fork from every completing. This contains the changes to remove the need for that restart. This set of changes is split into several parts: - The first part makes PIDTYPE_TGID a proper pid type instead something only for very special cases. The part starts using PIDTYPE_TGID enough so that in __send_signal where signals are actually delivered we know if the signal is being sent to a a group of processes or just a single process. - With that prep work out of the way the logic in fork is modified so that fork logically makes signals received while it is running appear to be received after the fork completes" * 'siginfo-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (22 commits) signal: Don't send signals to tasks that don't exist signal: Don't restart fork when signals come in. fork: Have new threads join on-going signal group stops fork: Skip setting TIF_SIGPENDING in ptrace_init_task signal: Add calculate_sigpending() fork: Unconditionally exit if a fatal signal is pending fork: Move and describe why the code examines PIDNS_ADDING signal: Push pid type down into complete_signal. signal: Push pid type down into __send_signal signal: Push pid type down into send_signal signal: Pass pid type into do_send_sig_info signal: Pass pid type into send_sigio_to_task & send_sigurg_to_task signal: Pass pid type into group_send_sig_info signal: Pass pid and pid type into send_sigqueue posix-timers: Noralize good_sigevent signal: Use PIDTYPE_TGID to clearly store where file signals will be sent pid: Implement PIDTYPE_TGID pids: Move the pgrp and session pid pointers from task_struct to signal_struct kvm: Don't open code task_pid in kvm_vcpu_ioctl pids: Compute task_tgid using signal->leader_pid ...

fs: fsnotify: account fsnotify metadata to kmemcg

2018-08-17T23:20:30Z

Patch series "Directed kmem charging", v8. The Linux kernel's memory cgroup allows limiting the memory usage of the jobs running on the system to provide isolation between the jobs. All the kernel memory allocated in the context of the job and marked with __GFP_ACCOUNT will also be included in the memory usage and be limited by the job's limit. The kernel memory can only be charged to the memcg of the process in whose context kernel memory was allocated. However there are cases where the allocated kernel memory should be charged to the memcg different from the current processes's memcg. This patch series contains two such concrete use-cases i.e. fsnotify and buffer_head. The fsnotify event objects can consume a lot of system memory for large or unlimited queues if there is either no or slow listener. The events are allocated in the context of the event producer. However they should be charged to the event consumer. Similarly the buffer_head objects can be allocated in a memcg different from the memcg of the page for which buffer_head objects are being allocated. To solve this issue, this patch series introduces mechanism to charge kernel memory to a given memcg. In case of fsnotify events, the memcg of the consumer can be used for charging and for buffer_head, the memcg of the page can be charged. For directed charging, the caller can use the scope API memalloc_[un]use_memcg() to specify the memcg to charge for all the __GFP_ACCOUNT allocations within the scope. This patch (of 2): A lot of memory can be consumed by the events generated for the huge or unlimited queues if there is either no or slow listener. This can cause system level memory pressure or OOMs. So, it's better to account the fsnotify kmem caches to the memcg of the listener. However the listener can be in a different memcg than the memcg of the producer and these allocations happen in the context of the event producer. This patch introduces remote memcg charging API which the producer can use to charge the allocations to the memcg of the listener. There are seven fsnotify kmem caches and among them allocations from dnotify_struct_cache, dnotify_mark_cache, fanotify_mark_cache and inotify_inode_mark_cachep happens in the context of syscall from the listener. So, SLAB_ACCOUNT is enough for these caches. The objects from fsnotify_mark_connector_cachep are not accounted as they are small compared to the notification mark or events and it is unclear whom to account connector to since it is shared by all events attached to the inode. The allocations from the event caches happen in the context of the event producer. For such caches we will need to remote charge the allocations to the listener's memcg. Thus we save the memcg reference in the fsnotify_group structure of the listener. This patch has also moved the members of fsnotify_group to keep the size same, at least for 64 bit build, even with additional member by filling the holes. [shakeelb@google.com: use GFP_KERNEL_ACCOUNT rather than open-coding it] Link: http://lkml.kernel.org/r/20180702215439.211597-1-shakeelb@google.com Link: http://lkml.kernel.org/r/20180627191250.209150-2-shakeelb@google.com Signed-off-by: Shakeel Butt Acked-by: Johannes Weiner Cc: Michal Hocko Cc: Jan Kara Cc: Amir Goldstein Cc: Greg Thelen Cc: Vladimir Davydov Cc: Roman Gushchin Cc: Alexander Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Merge tag 'for-4.19/block-20180812' of git://git.kernel.dk/linux-block

2018-08-14T17:23:25Z

Pull block updates from Jens Axboe: "First pull request for this merge window, there will also be a followup request with some stragglers. This pull request contains: - Fix for a thundering heard issue in the wbt block code (Anchal Agarwal) - A few NVMe pull requests: * Improved tracepoints (Keith) * Larger inline data support for RDMA (Steve Wise) * RDMA setup/teardown fixes (Sagi) * Effects log suppor for NVMe target (Chaitanya Kulkarni) * Buffered IO suppor for NVMe target (Chaitanya Kulkarni) * TP4004 (ANA) support (Christoph) * Various NVMe fixes - Block io-latency controller support. Much needed support for properly containing block devices. (Josef) - Series improving how we handle sense information on the stack (Kees) - Lightnvm fixes and updates/improvements (Mathias/Javier et al) - Zoned device support for null_blk (Matias) - AIX partition fixes (Mauricio Faria de Oliveira) - DIF checksum code made generic (Max Gurtovoy) - Add support for discard in iostats (Michael Callahan / Tejun) - Set of updates for BFQ (Paolo) - Removal of async write support for bsg (Christoph) - Bio page dirtying and clone fixups (Christoph) - Set of bcache fix/changes (via Coly) - Series improving blk-mq queue setup/teardown speed (Ming) - Series improving merging performance on blk-mq (Ming) - Lots of other fixes and cleanups from a slew of folks" * tag 'for-4.19/block-20180812' of git://git.kernel.dk/linux-block: (190 commits) blkcg: Make blkg_root_lookup() work for queues in bypass mode bcache: fix error setting writeback_rate through sysfs interface null_blk: add lock drop/acquire annotation Blk-throttle: reduce tail io latency when iops limit is enforced block: paride: pd: mark expected switch fall-throughs block: Ensure that a request queue is dissociated from the cgroup controller block: Introduce blk_exit_queue() blkcg: Introduce blkg_root_lookup() block: Remove two superfluous #include directives blk-mq: count the hctx as active before allocating tag block: bvec_nr_vecs() returns value for wrong slab bcache: trivial - remove tailing backslash in macro BTREE_FLAG bcache: make the pr_err statement used for ENOENT only in sysfs_attatch section bcache: set max writeback rate when I/O request is idle bcache: add code comments for bset.c bcache: fix mistaken comments in request.c bcache: fix mistaken code comments in bcache.h bcache: add a comment in super.c bcache: avoid unncessary cache prefetch bch_btree_node_get() bcache: display rate debug parameters to 0 when writeback is not running ...