user/sven/linux.git/kernel/fork.c, branch v4.9.5

mm: Add a user_ns owner to mm_struct and fix ptrace permission checks

2017-01-06T09:40:13Z

commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream. During exec dumpable is cleared if the file that is being executed is not readable by the user executing the file. A bug in ptrace_may_access allows reading the file if the executable happens to enter into a subordinate user namespace (aka clone(CLONE_NEWUSER), unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER). This problem is fixed with only necessary userspace breakage by adding a user namespace owner to mm_struct, captured at the time of exec, so it is clear in which user namespace CAP_SYS_PTRACE must be present in to be able to safely give read permission to the executable. The function ptrace_may_access is modified to verify that the ptracer has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns. This ensures that if the task changes it's cred into a subordinate user namespace it does not become ptraceable. The function ptrace_attach is modified to only set PT_PTRACE_CAP when CAP_SYS_PTRACE is held over task->mm->user_ns. The intent of PT_PTRACE_CAP is to be a flag to note that whatever permission changes the task might go through the tracer has sufficient permissions for it not to be an issue. task->cred->user_ns is always the same as or descendent of mm->user_ns. Which guarantees that having CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks credentials. To prevent regressions mm->dumpable and mm->user_ns are not considered when a task has no mm. As simply failing ptrace_may_attach causes regressions in privileged applications attempting to read things such as /proc//stat Acked-by: Kees Cook Tested-by: Cyrill Gorcunov Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces") Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman

fork: Add task stack refcounting sanity check and prevent premature task stack freeing

2016-11-01T06:39:17Z

If something goes wrong with task stack refcounting and a stack refcount hits zero too early, warn and leak it rather than potentially freeing it early (and silently). Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/f29119c783a9680a4b4656e751b6123917ace94b.1477926663.git.luto@kernel.org Signed-off-by: Ingo Molnar

Merge tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

2016-10-15T17:03:15Z

Pull gcc plugins update from Kees Cook: "This adds a new gcc plugin named "latent_entropy". It is designed to extract as much possible uncertainty from a running system at boot time as possible, hoping to capitalize on any possible variation in CPU operation (due to runtime data differences, hardware differences, SMP ordering, thermal timing variation, cache behavior, etc). At the very least, this plugin is a much more comprehensive example for how to manipulate kernel code using the gcc plugin internals" * tag 'gcc-plugins-v4.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux: latent_entropy: Mark functions with __latent_entropy gcc-plugins: Add latent_entropy plugin

latent_entropy: Mark functions with __latent_entropy

2016-10-10T21:51:45Z

The __latent_entropy gcc attribute can be used only on functions and variables. If it is on a function then the plugin will instrument it for gathering control-flow entropy. If the attribute is on a variable then the plugin will initialize it with random contents. The variable must be an integer, an integer array type or a structure with integer fields. These specific functions have been selected because they are init functions (to help gather boot-time entropy), are called at unpredictable times, or they have variable loops, each of which provide some level of latent entropy. Signed-off-by: Emese Revfy [kees: expanded commit message] Signed-off-by: Kees Cook

gcc-plugins: Add latent_entropy plugin

2016-10-10T21:51:44Z

This adds a new gcc plugin named "latent_entropy". It is designed to extract as much possible uncertainty from a running system at boot time as possible, hoping to capitalize on any possible variation in CPU operation (due to runtime data differences, hardware differences, SMP ordering, thermal timing variation, cache behavior, etc). At the very least, this plugin is a much more comprehensive example for how to manipulate kernel code using the gcc plugin internals. The need for very-early boot entropy tends to be very architecture or system design specific, so this plugin is more suited for those sorts of special cases. The existing kernel RNG already attempts to extract entropy from reliable runtime variation, but this plugin takes the idea to a logical extreme by permuting a global variable based on any variation in code execution (e.g. a different value (and permutation function) is used to permute the global based on loop count, case statement, if/then/else branching, etc). To do this, the plugin starts by inserting a local variable in every marked function. The plugin then adds logic so that the value of this variable is modified by randomly chosen operations (add, xor and rol) and random values (gcc generates separate static values for each location at compile time and also injects the stack pointer at runtime). The resulting value depends on the control flow path (e.g., loops and branches taken). Before the function returns, the plugin mixes this local variable into the latent_entropy global variable. The value of this global variable is added to the kernel entropy pool in do_one_initcall() and _do_fork(), though it does not credit any bytes of entropy to the pool; the contents of the global are just used to mix the pool. Additionally, the plugin can pre-initialize arrays with build-time random contents, so that two different kernel builds running on identical hardware will not have the same starting values. Signed-off-by: Emese Revfy [kees: expanded commit message and code comments] Signed-off-by: Kees Cook

thp: reduce usage of huge zero page's atomic counter

2016-10-08T01:46:28Z

The global zero page is used to satisfy an anonymous read fault. If THP(Transparent HugePage) is enabled then the global huge zero page is used. The global huge zero page uses an atomic counter for reference counting and is allocated/freed dynamically according to its counter value. CPU time spent on that counter will greatly increase if there are a lot of processes doing anonymous read faults. This patch proposes a way to reduce the access to the global counter so that the CPU load can be reduced accordingly. To do this, a new flag of the mm_struct is introduced: MMF_USED_HUGE_ZERO_PAGE. With this flag, the process only need to touch the global counter in two cases: 1 The first time it uses the global huge zero page; 2 The time when mm_user of its mm_struct reaches zero. Note that right now, the huge zero page is eligible to be freed as soon as its last use goes away. With this patch, the page will not be eligible to be freed until the exit of the last process from which it was ever used. And with the use of mm_user, the kthread is not eligible to use huge zero page either. Since no kthread is using huge zero page today, there is no difference after applying this patch. But if that is not desired, I can change it to when mm_count reaches zero. Case used for test on Haswell EP: usemem -n 72 --readonly -j 0x200000 100G Which spawns 72 processes and each will mmap 100G anonymous space and then do read only access to that space sequentially with a step of 2MB. CPU cycles from perf report for base commit: 54.03% usemem [kernel.kallsyms] [k] get_huge_zero_page CPU cycles from perf report for this commit: 0.11% usemem [kernel.kallsyms] [k] mm_get_huge_zero_page Performance(throughput) of the workload for base commit: 1784430792 Performance(throughput) of the workload for this commit: 4726928591 164% increase. Runtime of the workload for base commit: 707592 us Runtime of the workload for this commit: 303970 us 50% drop. Link: http://lkml.kernel.org/r/fe51a88f-446a-4622-1363-ad1282d71385@intel.com Signed-off-by: Aaron Lu Cc: Sergey Senozhatsky Cc: "Kirill A. Shutemov" Cc: Dave Hansen Cc: Tim Chen Cc: Huang Ying Cc: Vlastimil Babka Cc: Jerome Marchand Cc: Andrea Arcangeli Cc: Mel Gorman Cc: Ebru Akagunduz Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm, oom: get rid of signal_struct::oom_victims

2016-10-08T01:46:27Z

After "oom: keep mm of the killed task available" we can safely detect an oom victim by checking task->signal->oom_mm so we do not need the signal_struct counter anymore so let's get rid of it. This alone wouldn't be sufficient for nommu archs because exit_oom_victim doesn't hide the process from the oom killer anymore. We can, however, mark the mm with a MMF flag in __mmput. We can reuse MMF_OOM_REAPED and rename it to a more generic MMF_OOM_SKIP. Link: http://lkml.kernel.org/r/1472119394-11342-6-git-send-email-mhocko@kernel.org Signed-off-by: Michal Hocko Cc: Tetsuo Handa Cc: Oleg Nesterov Cc: David Rientjes Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kernel, oom: fix potential pgd_lock deadlock from __mmdrop

2016-10-08T01:46:27Z

Lockdep complains that __mmdrop is not safe from the softirq context: ================================= [ INFO: inconsistent lock state ] 4.6.0-oomfortification2-00011-geeb3eadeab96-dirty #949 Tainted: G W --------------------------------- inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. swapper/1/0 [HC0[0]:SC1[1]:HE1:SE0] takes: (pgd_lock){+.?...}, at: pgd_free+0x19/0x6b {SOFTIRQ-ON-W} state was registered at: __lock_acquire+0xa06/0x196e lock_acquire+0x139/0x1e1 _raw_spin_lock+0x32/0x41 __change_page_attr_set_clr+0x2a5/0xacd change_page_attr_set_clr+0x16f/0x32c set_memory_nx+0x37/0x3a free_init_pages+0x9e/0xc7 alternative_instructions+0xa2/0xb3 check_bugs+0xe/0x2d start_kernel+0x3ce/0x3ea x86_64_start_reservations+0x2a/0x2c x86_64_start_kernel+0x17a/0x18d irq event stamp: 105916 hardirqs last enabled at (105916): free_hot_cold_page+0x37e/0x390 hardirqs last disabled at (105915): free_hot_cold_page+0x2c1/0x390 softirqs last enabled at (105878): _local_bh_enable+0x42/0x44 softirqs last disabled at (105879): irq_exit+0x6f/0xd1 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(pgd_lock); lock(pgd_lock); *** DEADLOCK *** 1 lock held by swapper/1/0: #0: (rcu_callback){......}, at: rcu_process_callbacks+0x390/0x800 stack backtrace: CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 4.6.0-oomfortification2-00011-geeb3eadeab96-dirty #949 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 Call Trace: print_usage_bug.part.25+0x259/0x268 mark_lock+0x381/0x567 __lock_acquire+0x993/0x196e lock_acquire+0x139/0x1e1 _raw_spin_lock+0x32/0x41 pgd_free+0x19/0x6b __mmdrop+0x25/0xb9 __put_task_struct+0x103/0x11e delayed_put_task_struct+0x157/0x15e rcu_process_callbacks+0x660/0x800 __do_softirq+0x1ec/0x4d5 irq_exit+0x6f/0xd1 smp_apic_timer_interrupt+0x42/0x4d apic_timer_interrupt+0x8e/0xa0 arch_cpu_idle+0xf/0x11 default_idle_call+0x32/0x34 cpu_startup_entry+0x20c/0x399 start_secondary+0xfe/0x101 More over commit a79e53d85683 ("x86/mm: Fix pgd_lock deadlock") was explicit about pgd_lock not to be called from the irq context. This means that __mmdrop called from free_signal_struct has to be postponed to a user context. We already have a similar mechanism for mmput_async so we can use it here as well. This is safe because mm_count is pinned by mm_users. This fixes bug introduced by "oom: keep mm of the killed task available" Link: http://lkml.kernel.org/r/1472119394-11342-5-git-send-email-mhocko@kernel.org Signed-off-by: Michal Hocko Cc: Tetsuo Handa Cc: Oleg Nesterov Cc: David Rientjes Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

oom: keep mm of the killed task available

2016-10-08T01:46:27Z

oom_reap_task has to call exit_oom_victim in order to make sure that the oom vicim will not block the oom killer for ever. This is, however, opening new problems (e.g oom_killer_disable exclusion - see commit 74070542099c ("oom, suspend: fix oom_reaper vs. oom_killer_disable race")). exit_oom_victim should be only called from the victim's context ideally. One way to achieve this would be to rely on per mm_struct flags. We already have MMF_OOM_REAPED to hide a task from the oom killer since "mm, oom: hide mm which is shared with kthread or global init". The problem is that the exit path: do_exit exit_mm tsk->mm = NULL; mmput __mmput exit_oom_victim doesn't guarantee that exit_oom_victim will get called in a bounded amount of time. At least exit_aio depends on IO which might get blocked due to lack of memory and who knows what else is lurking there. This patch takes a different approach. We remember tsk->mm into the signal_struct and bind it to the signal struct life time for all oom victims. __oom_reap_task_mm as well as oom_scan_process_thread do not have to rely on find_lock_task_mm anymore and they will have a reliable reference to the mm struct. As a result all the oom specific communication inside the OOM killer can be done via tsk->signal->oom_mm. Increasing the signal_struct for something as unlikely as the oom killer is far from ideal but this approach will make the code much more reasonable and long term we even might want to move task->mm into the signal_struct anyway. In the next step we might want to make the oom killer exclusion and access to memory reserves completely independent which would be also nice. Link: http://lkml.kernel.org/r/1472119394-11342-4-git-send-email-mhocko@kernel.org Signed-off-by: Michal Hocko Cc: Tetsuo Handa Cc: Oleg Nesterov Cc: David Rientjes Cc: Vladimir Davydov Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

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

2016-10-06T16:52:23Z

Pull namespace updates from Eric Biederman: "This set of changes is a number of smaller things that have been overlooked in other development cycles focused on more fundamental change. The devpts changes are small things that were a distraction until we managed to kill off DEVPTS_MULTPLE_INSTANCES. There is an trivial regression fix to autofs for the unprivileged mount changes that went in last cycle. A pair of ioctls has been added by Andrey Vagin making it is possible to discover the relationships between namespaces when referring to them through file descriptors. The big user visible change is starting to add simple resource limits to catch programs that misbehave. With namespaces in general and user namespaces in particular allowing users to use more kinds of resources, it has become important to have something to limit errant programs. Because the purpose of these limits is to catch errant programs the code needs to be inexpensive to use as it always on, and the default limits need to be high enough that well behaved programs on well behaved systems don't encounter them. To this end, after some review I have implemented per user per user namespace limits, and use them to limit the number of namespaces. The limits being per user mean that one user can not exhause the limits of another user. The limits being per user namespace allow contexts where the limit is 0 and security conscious folks can remove from their threat anlysis the code used to manage namespaces (as they have historically done as it root only). At the same time the limits being per user namespace allow other parts of the system to use namespaces. Namespaces are increasingly being used in application sand boxing scenarios so an all or nothing disable for the entire system for the security conscious folks makes increasing use of these sandboxes impossible. There is also added a limit on the maximum number of mounts present in a single mount namespace. It is nontrivial to guess what a reasonable system wide limit on the number of mount structure in the kernel would be, especially as it various based on how a system is using containers. A limit on the number of mounts in a mount namespace however is much easier to understand and set. In most cases in practice only about 1000 mounts are used. Given that some autofs scenarious have the potential to be 30,000 to 50,000 mounts I have set the default limit for the number of mounts at 100,000 which is well above every known set of users but low enough that the mount hash tables don't degrade unreaonsably. These limits are a start. I expect this estabilishes a pattern that other limits for resources that namespaces use will follow. There has been interest in making inotify event limits per user per user namespace as well as interest expressed in making details about what is going on in the kernel more visible" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (28 commits) autofs: Fix automounts by using current_real_cred()->uid mnt: Add a per mount namespace limit on the number of mounts netns: move {inc,dec}_net_namespaces into #ifdef nsfs: Simplify __ns_get_path tools/testing: add a test to check nsfs ioctl-s nsfs: add ioctl to get a parent namespace nsfs: add ioctl to get an owning user namespace for ns file descriptor kernel: add a helper to get an owning user namespace for a namespace devpts: Change the owner of /dev/pts/ptmx to the mounter of /dev/pts devpts: Remove sync_filesystems devpts: Make devpts_kill_sb safe if fsi is NULL devpts: Simplify devpts_mount by using mount_nodev devpts: Move the creation of /dev/pts/ptmx into fill_super devpts: Move parse_mount_options into fill_super userns: When the per user per user namespace limit is reached return ENOSPC userns; Document per user per user namespace limits. mntns: Add a limit on the number of mount namespaces. netns: Add a limit on the number of net namespaces cgroupns: Add a limit on the number of cgroup namespaces ipcns: Add a limit on the number of ipc namespaces ...