linux/ipc/util.h, branch v3.12

ipc: fix race with LSMs

2013-09-24T16:36:53Z

Currently, IPC mechanisms do security and auditing related checks under RCU. However, since security modules can free the security structure, for example, through selinux_[sem,msg_queue,shm]_free_security(), we can race if the structure is freed before other tasks are done with it, creating a use-after-free condition. Manfred illustrates this nicely, for instance with shared mem and selinux: -> do_shmat calls rcu_read_lock() -> do_shmat calls shm_object_check(). Checks that the object is still valid - but doesn't acquire any locks. Then it returns. -> do_shmat calls security_shm_shmat (e.g. selinux_shm_shmat) -> selinux_shm_shmat calls ipc_has_perm() -> ipc_has_perm accesses ipc_perms->security shm_close() -> shm_close acquires rw_mutex & shm_lock -> shm_close calls shm_destroy -> shm_destroy calls security_shm_free (e.g. selinux_shm_free_security) -> selinux_shm_free_security calls ipc_free_security(&shp->shm_perm) -> ipc_free_security calls kfree(ipc_perms->security) This patch delays the freeing of the security structures after all RCU readers are done. Furthermore it aligns the security life cycle with that of the rest of IPC - freeing them based on the reference counter. For situations where we need not free security, the current behavior is kept. Linus states: "... the old behavior was suspect for another reason too: having the security blob go away from under a user sounds like it could cause various other problems anyway, so I think the old code was at least _prone_ to bugs even if it didn't have catastrophic behavior." I have tested this patch with IPC testcases from LTP on both my quad-core laptop and on a 64 core NUMA server. In both cases selinux is enabled, and tests pass for both voluntary and forced preemption models. While the mentioned races are theoretical (at least no one as reported them), I wanted to make sure that this new logic doesn't break anything we weren't aware of. Suggested-by: Linus Torvalds Signed-off-by: Davidlohr Bueso Acked-by: Manfred Spraul Signed-off-by: Linus Torvalds

ipc: drop ipc_lock_check

2013-09-11T22:59:45Z

No remaining users, we now use ipc_obtain_object_check(). Signed-off-by: Davidlohr Bueso Cc: Sedat Dilek Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: drop ipc_lock_by_ptr

2013-09-11T22:59:44Z

After previous cleanups and optimizations, this function is no longer heavily used and we don't have a good reason to keep it. Update the few remaining callers and get rid of it. Signed-off-by: Davidlohr Bueso Cc: Sedat Dilek Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: rename ids->rw_mutex

2013-09-11T22:59:42Z

Since in some situations the lock can be shared for readers, we shouldn't be calling it a mutex, rename it to rwsem. Signed-off-by: Davidlohr Bueso Tested-by: Sedat Dilek Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: drop ipcctl_pre_down

2013-09-11T22:59:39Z

Now that sem, msgque and shm, through *_down(), all use the lockless variant of ipcctl_pre_down(), go ahead and delete it. [akpm@linux-foundation.org: fix function name in kerneldoc, cleanups] Signed-off-by: Davidlohr Bueso Tested-by: Sedat Dilek Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: close open coded spin lock calls

2013-07-09T17:33:27Z

Signed-off-by: Davidlohr Bueso Cc: Andi Kleen Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: introduce ipc object locking helpers

2013-07-09T17:33:27Z

Simple helpers around the (kern_ipc_perm *)->lock spinlock. Signed-off-by: Davidlohr Bueso Cc: Andi Kleen Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc,sem: fine grained locking for semtimedop

2013-05-01T15:12:58Z

Introduce finer grained locking for semtimedop, to handle the common case of a program wanting to manipulate one semaphore from an array with multiple semaphores. If the call is a semop manipulating just one semaphore in an array with multiple semaphores, only take the lock for that semaphore itself. If the call needs to manipulate multiple semaphores, or another caller is in a transaction that manipulates multiple semaphores, the sem_array lock is taken, as well as all the locks for the individual semaphores. On a 24 CPU system, performance numbers with the semop-multi test with N threads and N semaphores, look like this: vanilla Davidlohr's Davidlohr's + Davidlohr's + threads patches rwlock patches v3 patches 10 610652 726325 1783589 2142206 20 341570 365699 1520453 1977878 30 288102 307037 1498167 2037995 40 290714 305955 1612665 2256484 50 288620 312890 1733453 2650292 60 289987 306043 1649360 2388008 70 291298 306347 1723167 2717486 80 290948 305662 1729545 2763582 90 290996 306680 1736021 2757524 100 292243 306700 1773700 3059159 [davidlohr.bueso@hp.com: do not call sem_lock when bogus sma] [davidlohr.bueso@hp.com: make refcounter atomic] Signed-off-by: Rik van Riel Suggested-by: Linus Torvalds Acked-by: Davidlohr Bueso Cc: Chegu Vinod Cc: Jason Low Reviewed-by: Michel Lespinasse Cc: Peter Hurley Cc: Stanislav Kinsbursky Tested-by: Emmanuel Benisty Tested-by: Sedat Dilek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc,sem: do not hold ipc lock more than necessary

2013-05-01T15:12:58Z

Instead of holding the ipc lock for permissions and security checks, among others, only acquire it when necessary. Some numbers.... 1) With Rik's semop-multi.c microbenchmark we can see the following results: Baseline (3.9-rc1): cpus 4, threads: 256, semaphores: 128, test duration: 30 secs total operations: 151452270, ops/sec 5048409 + 59.40% a.out [kernel.kallsyms] [k] _raw_spin_lock + 6.14% a.out [kernel.kallsyms] [k] sys_semtimedop + 3.84% a.out [kernel.kallsyms] [k] avc_has_perm_flags + 3.64% a.out [kernel.kallsyms] [k] __audit_syscall_exit + 2.06% a.out [kernel.kallsyms] [k] copy_user_enhanced_fast_string + 1.86% a.out [kernel.kallsyms] [k] ipc_lock With this patchset: cpus 4, threads: 256, semaphores: 128, test duration: 30 secs total operations: 273156400, ops/sec 9105213 + 18.54% a.out [kernel.kallsyms] [k] _raw_spin_lock + 11.72% a.out [kernel.kallsyms] [k] sys_semtimedop + 7.70% a.out [kernel.kallsyms] [k] ipc_has_perm.isra.21 + 6.58% a.out [kernel.kallsyms] [k] avc_has_perm_flags + 6.54% a.out [kernel.kallsyms] [k] __audit_syscall_exit + 4.71% a.out [kernel.kallsyms] [k] ipc_obtain_object_check 2) While on an Oracle swingbench DSS (data mining) workload the improvements are not as exciting as with Rik's benchmark, we can see some positive numbers. For an 8 socket machine the following are the percentages of %sys time incurred in the ipc lock: Baseline (3.9-rc1): 100 swingbench users: 8,74% 400 swingbench users: 21,86% 800 swingbench users: 84,35% With this patchset: 100 swingbench users: 8,11% 400 swingbench users: 19,93% 800 swingbench users: 77,69% [riel@redhat.com: fix two locking bugs] [sasha.levin@oracle.com: prevent releasing RCU read lock twice in semctl_main] [akpm@linux-foundation.org: coding-style fixes] Signed-off-by: Davidlohr Bueso Signed-off-by: Rik van Riel Reviewed-by: Chegu Vinod Acked-by: Michel Lespinasse Cc: Rik van Riel Cc: Jason Low Cc: Emmanuel Benisty Cc: Peter Hurley Cc: Stanislav Kinsbursky Tested-by: Sedat Dilek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: introduce lockless pre_down ipcctl

2013-05-01T15:12:58Z

Various forms of ipc use ipcctl_pre_down() to retrieve an ipc object and check permissions, mostly for IPC_RMID and IPC_SET commands. Introduce ipcctl_pre_down_nolock(), a lockless version of this function. The locking version is retained, yet modified to call the nolock version without affecting its semantics, thus transparent to all ipc callers. Signed-off-by: Davidlohr Bueso Signed-off-by: Rik van Riel Suggested-by: Linus Torvalds Cc: Chegu Vinod Cc: Emmanuel Benisty Cc: Jason Low Cc: Michel Lespinasse Cc: Peter Hurley Cc: Stanislav Kinsbursky Tested-by: Sedat Dilek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds