kernel/linux.git/ipc/shm.c, branch v3.12.43

shmdt: use i_size_read() instead of ->i_size

2015-04-09T11:14:25+00:00

commit 07a46ed27dc6344de831a450df82336270a157a9 upstream. Andrew Morton noted http://lkml.kernel.org/r/20141104142027.a7a0d010772d84560b445f59@linux-foundation.org that the shmdt uses inode->i_size outside of i_mutex being held. There is one more case in shm.c in shm_destroy(). This converts both users over to use i_size_read(). Signed-off-by: Dave Hansen Cc: Manfred Spraul Cc: Davidlohr Bueso Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Jiri Slaby

ipc/shm.c: fix overly aggressive shmdt() when calls span multiple segments

2015-04-09T11:14:25+00:00

commit d3c97900b427b8d5a476fdfe484267f09df418d6 upstream. This is a highly-contrived scenario. But, a single shmdt() call can be induced in to unmapping memory from mulitple shm segments. Example code is here: http://www.sr71.net/~dave/intel/shmfun.c The fix is pretty simple: Record the 'struct file' for the first VMA we encounter and then stick to it. Decline to unmap anything not from the same file and thus the same segment. I found this by inspection and the odds of anyone hitting this in practice are pretty darn small. Lightly tested, but it's a pretty small patch. Signed-off-by: Dave Hansen Cc: Manfred Spraul Reviewed-by: Davidlohr Bueso Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Jiri Slaby

ipc,shm: fix shm_file deletion races

2013-11-29T19:27:54+00:00

commit a399b29dfbaaaf91162b2dc5a5875dd51bbfa2a1 upstream. When IPC_RMID races with other shm operations there's potential for use-after-free of the shm object's associated file (shm_file). Here's the race before this patch: TASK 1 TASK 2 ------ ------ shm_rmid() ipc_lock_object() shmctl() shp = shm_obtain_object_check() shm_destroy() shum_unlock() fput(shp->shm_file) ipc_lock_object() shmem_lock(shp->shm_file) The oops is caused because shm_destroy() calls fput() after dropping the ipc_lock. fput() clears the file's f_inode, f_path.dentry, and f_path.mnt, which causes various NULL pointer references in task 2. I reliably see the oops in task 2 if with shmlock, shmu This patch fixes the races by: 1) set shm_file=NULL in shm_destroy() while holding ipc_object_lock(). 2) modify at risk operations to check shm_file while holding ipc_object_lock(). Example workloads, which each trigger oops... Workload 1: while true; do id=$(shmget 1 4096) shm_rmid $id & shmlock $id & wait done The oops stack shows accessing NULL f_inode due to racing fput: _raw_spin_lock shmem_lock SyS_shmctl Workload 2: while true; do id=$(shmget 1 4096) shmat $id 4096 & shm_rmid $id & wait done The oops stack is similar to workload 1 due to NULL f_inode: touch_atime shmem_mmap shm_mmap mmap_region do_mmap_pgoff do_shmat SyS_shmat Workload 3: while true; do id=$(shmget 1 4096) shmlock $id shm_rmid $id & shmunlock $id & wait done The oops stack shows second fput tripping on an NULL f_inode. The first fput() completed via from shm_destroy(), but a racing thread did a get_file() and queued this fput(): locks_remove_flock __fput ____fput task_work_run do_notify_resume int_signal Fixes: c2c737a0461e ("ipc,shm: shorten critical region for shmat") Fixes: 2caacaa82a51 ("ipc,shm: shorten critical region for shmctl") Signed-off-by: Greg Thelen Cc: Davidlohr Bueso Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

ipc,shm: correct error return value in shmctl (SHM_UNLOCK)

2013-11-29T19:27:53+00:00

commit 3a72660b07d86d60457ca32080b1ce8c2b628ee2 upstream. Commit 2caacaa82a51 ("ipc,shm: shorten critical region for shmctl") restructured the ipc shm to shorten critical region, but introduced a path where the return value could be -EPERM, even if the operation actually was performed. Before the commit, the err return value was reset by the return value from security_shm_shmctl() after the if (!ns_capable(...)) statement. Now, we still exit the if statement with err set to -EPERM, and in the case of SHM_UNLOCK, it is not reset at all, and used as the return value from shmctl. To fix this, we only set err when errors occur, leaving the fallthrough case alone. Signed-off-by: Jesper Nilsson Cc: Davidlohr Bueso Cc: Rik van Riel Cc: Michel Lespinasse Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

ipc: fix race with LSMs

2013-09-24T16:36:53+00:00

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, shm: drop shm_lock_check

2013-09-11T22:59:44+00:00

This function was replaced by a the lockless shm_obtain_object_check(), and no longer has any users. 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, shm: guard against non-existant vma in shmdt(2)

2013-09-11T22:59:44+00:00

When !CONFIG_MMU there's a chance we can derefence a NULL pointer when the VM area isn't found - check the return value of find_vma(). Also, remove the redundant -EINVAL return: retval is set to the proper return code and *only* changed to 0, when we actually unmap the segments. 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

2013-09-11T22:59:42+00:00

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,shm: shorten critical region for shmat

2013-09-11T22:59:42+00:00

Similar to other system calls, acquire the kern_ipc_perm lock after doing the initial permission and security checks. [sasha.levin@oracle.com: dont leave do_shmat with rcu lock held] Signed-off-by: Davidlohr Bueso Tested-by: Sedat Dilek Cc: Rik van Riel Cc: Manfred Spraul Signed-off-by: Sasha Levin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc,shm: cleanup do_shmat pasta

2013-09-11T22:59:42+00:00

Clean up some of the messy do_shmat() spaghetti code, getting rid of out_free and out_put_dentry labels. This makes shortening the critical region of this function in the next patch a little easier to do and read. 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