user/sven/linux.git/kernel/futex.c, branch v4.4.130

futex: Remove requirement for lock_page() in get_futex_key()

2018-04-13T17:50:24Z

commit 65d8fc777f6dcfee12785c057a6b57f679641c90 upstream. When dealing with key handling for shared futexes, we can drastically reduce the usage/need of the page lock. 1) For anonymous pages, the associated futex object is the mm_struct which does not require the page lock. 2) For inode based, keys, we can check under RCU read lock if the page mapping is still valid and take reference to the inode. This just leaves one rare race that requires the page lock in the slow path when examining the swapcache. Additionally realtime users currently have a problem with the page lock being contended for unbounded periods of time during futex operations. Task A get_futex_key() lock_page() ---> preempted Now any other task trying to lock that page will have to wait until task A gets scheduled back in, which is an unbound time. With this patch, we pretty much have a lockless futex_get_key(). Experiments show that this patch can boost/speedup the hashing of shared futexes with the perf futex benchmarks (which is good for measuring such change) by up to 45% when there are high (> 100) thread counts on a 60 core Westmere. Lower counts are pretty much in the noise range or less than 10%, but mid range can be seen at over 30% overall throughput (hash ops/sec). This makes anon-mem shared futexes much closer to its private counterpart. Signed-off-by: Mel Gorman [ Ported on top of thp refcount rework, changelog, comments, fixes. ] Signed-off-by: Davidlohr Bueso Reviewed-by: Thomas Gleixner Cc: Chris Mason Cc: Darren Hart Cc: Hugh Dickins Cc: Linus Torvalds Cc: Mel Gorman Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: dave@stgolabs.net Link: http://lkml.kernel.org/r/1455045314-8305-3-git-send-email-dave@stgolabs.net Signed-off-by: Ingo Molnar Signed-off-by: Chenbo Feng Signed-off-by: Greg Kroah-Hartman

futex: Prevent overflow by strengthen input validation

2018-01-23T18:50:14Z

commit fbe0e839d1e22d88810f3ee3e2f1479be4c0aa4a upstream. UBSAN reports signed integer overflow in kernel/futex.c: UBSAN: Undefined behaviour in kernel/futex.c:2041:18 signed integer overflow: 0 - -2147483648 cannot be represented in type 'int' Add a sanity check to catch negative values of nr_wake and nr_requeue. Signed-off-by: Li Jinyue Signed-off-by: Thomas Gleixner Cc: peterz@infradead.org Cc: dvhart@infradead.org Link: https://lkml.kernel.org/r/1513242294-31786-1-git-send-email-lijinyue@huawei.com Signed-off-by: Greg Kroah-Hartman

futex: Replace barrier() in unqueue_me() with READ_ONCE()

2018-01-17T08:35:27Z

commit 29b75eb2d56a714190a93d7be4525e617591077a upstream. Commit e91467ecd1ef ("bug in futex unqueue_me") introduced a barrier() in unqueue_me() to prevent the compiler from rereading the lock pointer which might change after a check for NULL. Replace the barrier() with a READ_ONCE() for the following reasons: 1) READ_ONCE() is a weaker form of barrier() that affects only the specific load operation, while barrier() is a general compiler level memory barrier. READ_ONCE() was not available at the time when the barrier was added. 2) Aside of that READ_ONCE() is descriptive and self explainatory while a barrier without comment is not clear to the casual reader. No functional change. [ tglx: Massaged changelog ] Signed-off-by: Jianyu Zhan Acked-by: Christian Borntraeger Acked-by: Darren Hart Cc: dave@stgolabs.net Cc: peterz@infradead.org Cc: linux@rasmusvillemoes.dk Cc: akpm@linux-foundation.org Cc: fengguang.wu@intel.com Cc: bigeasy@linutronix.de Link: http://lkml.kernel.org/r/1457314344-5685-1-git-send-email-nasa4836@gmail.com Signed-off-by: Thomas Gleixner Signed-off-by: Davidlohr Bueso Signed-off-by: Greg Kroah-Hartman

futex: Add missing error handling to FUTEX_REQUEUE_PI

2017-03-22T11:04:19Z

commit 9bbb25afeb182502ca4f2c4f3f88af0681b34cae upstream. Thomas spotted that fixup_pi_state_owner() can return errors and we fail to unlock the rt_mutex in that case. Reported-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Darren Hart Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: xlpang@redhat.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: dvhart@infradead.org Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170304093558.867401760@infradead.org Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Fix potential use-after-free in FUTEX_REQUEUE_PI

2017-03-22T11:04:19Z

commit c236c8e95a3d395b0494e7108f0d41cf36ec107c upstream. While working on the futex code, I stumbled over this potential use-after-free scenario. Dmitry triggered it later with syzkaller. pi_mutex is a pointer into pi_state, which we drop the reference on in unqueue_me_pi(). So any access to that pointer after that is bad. Since other sites already do rt_mutex_unlock() with hb->lock held, see for example futex_lock_pi(), simply move the unlock before unqueue_me_pi(). Reported-by: Dmitry Vyukov Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Darren Hart Cc: juri.lelli@arm.com Cc: bigeasy@linutronix.de Cc: xlpang@redhat.com Cc: rostedt@goodmis.org Cc: mathieu.desnoyers@efficios.com Cc: jdesfossez@efficios.com Cc: dvhart@infradead.org Cc: bristot@redhat.com Link: http://lkml.kernel.org/r/20170304093558.801744246@infradead.org Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Move futex_init() to core_initcall

2017-02-23T16:43:09Z

commit 25f71d1c3e98ef0e52371746220d66458eac75bc upstream. The UEVENT user mode helper is enabled before the initcalls are executed and is available when the root filesystem has been mounted. The user mode helper is triggered by device init calls and the executable might use the futex syscall. futex_init() is marked __initcall which maps to device_initcall, but there is no guarantee that futex_init() is invoked _before_ the first device init call which triggers the UEVENT user mode helper. If the user mode helper uses the futex syscall before futex_init() then the syscall crashes with a NULL pointer dereference because the futex subsystem has not been initialized yet. Move futex_init() to core_initcall so futexes are initialized before the root filesystem is mounted and the usermode helper becomes available. [ tglx: Rewrote changelog ] Signed-off-by: Yang Yang Cc: jiang.biao2@zte.com.cn Cc: jiang.zhengxiong@zte.com.cn Cc: zhong.weidong@zte.com.cn Cc: deng.huali@zte.com.cn Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1483085875-6130-1-git-send-email-yang.yang29@zte.com.cn Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Acknowledge a new waiter in counter before plist

2016-05-04T21:48:43Z

commit fe1bce9e2107ba3a8faffe572483b6974201a0e6 upstream. Otherwise an incoming waker on the dest hash bucket can miss the waiter adding itself to the plist during the lockless check optimization (small window but still the correct way of doing this); similarly to the decrement counterpart. Suggested-by: Peter Zijlstra Signed-off-by: Davidlohr Bueso Cc: Davidlohr Bueso Cc: bigeasy@linutronix.de Cc: dvhart@infradead.org Link: http://lkml.kernel.org/r/1461208164-29150-1-git-send-email-dave@stgolabs.net Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Handle unlock_pi race gracefully

2016-05-04T21:48:43Z

commit 89e9e66ba1b3bde9d8ea90566c2aee20697ad681 upstream. If userspace calls UNLOCK_PI unconditionally without trying the TID -> 0 transition in user space first then the user space value might not have the waiters bit set. This opens the following race: CPU0 CPU1 uval = get_user(futex) lock(hb) lock(hb) futex |= FUTEX_WAITERS .... unlock(hb) cmpxchg(futex, uval, newval) So the cmpxchg fails and returns -EINVAL to user space, which is wrong because the futex value is valid. To handle this (yes, yet another) corner case gracefully, check for a flag change and retry. [ tglx: Massaged changelog and slightly reworked implementation ] Fixes: ccf9e6a80d9e ("futex: Make unlock_pi more robust") Signed-off-by: Sebastian Andrzej Siewior Cc: Davidlohr Bueso Cc: Darren Hart Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1460723739-5195-1-git-send-email-bigeasy@linutronix.de Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

futex: Drop refcount if requeue_pi() acquired the rtmutex

2016-02-25T20:01:23Z

commit fb75a4282d0d9a3c7c44d940582c2d226cf3acfb upstream. If the proxy lock in the requeue loop acquires the rtmutex for a waiter then it acquired also refcount on the pi_state related to the futex, but the waiter side does not drop the reference count. Add the missing free_pi_state() call. Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Darren Hart Cc: Davidlohr Bueso Cc: Bhuvanesh_Surachari@mentor.com Cc: Andy Lowe Link: http://lkml.kernel.org/r/20151219200607.178132067@linutronix.de Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

ptrace: use fsuid, fsgid, effective creds for fs access checks

2016-02-25T20:01:16Z

commit caaee6234d05a58c5b4d05e7bf766131b810a657 upstream. By checking the effective credentials instead of the real UID / permitted capabilities, ensure that the calling process actually intended to use its credentials. To ensure that all ptrace checks use the correct caller credentials (e.g. in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS flag), use two new flags and require one of them to be set. The problem was that when a privileged task had temporarily dropped its privileges, e.g. by calling setreuid(0, user_uid), with the intent to perform following syscalls with the credentials of a user, it still passed ptrace access checks that the user would not be able to pass. While an attacker should not be able to convince the privileged task to perform a ptrace() syscall, this is a problem because the ptrace access check is reused for things in procfs. In particular, the following somewhat interesting procfs entries only rely on ptrace access checks: /proc/$pid/stat - uses the check for determining whether pointers should be visible, useful for bypassing ASLR /proc/$pid/maps - also useful for bypassing ASLR /proc/$pid/cwd - useful for gaining access to restricted directories that contain files with lax permissions, e.g. in this scenario: lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar drwx------ root root /root drwxr-xr-x root root /root/foobar -rw-r--r-- root root /root/foobar/secret Therefore, on a system where a root-owned mode 6755 binary changes its effective credentials as described and then dumps a user-specified file, this could be used by an attacker to reveal the memory layout of root's processes or reveal the contents of files he is not allowed to access (through /proc/$pid/cwd). [akpm@linux-foundation.org: fix warning] Signed-off-by: Jann Horn Acked-by: Kees Cook Cc: Casey Schaufler Cc: Oleg Nesterov Cc: Ingo Molnar Cc: James Morris Cc: "Serge E. Hallyn" Cc: Andy Shevchenko Cc: Andy Lutomirski Cc: Al Viro Cc: "Eric W. Biederman" Cc: Willy Tarreau Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman