user/sven/linux.git/ipc/sem.c, branch v5.4.27

Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()"

2020-02-28T16:22:20Z

commit edf28f4061afe4c2d9eb1c3323d90e882c1d6800 upstream. This reverts commit a97955844807e327df11aa33869009d14d6b7de0. Commit a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()") removes a lock that is needed. This leads to a process looping infinitely in exit_sem() and can also lead to a crash. There is a reproducer available in [1] and with the commit reverted the issue does not reproduce anymore. Using the reproducer found in [1] is fairly easy to reach a point where one of the child processes is looping infinitely in exit_sem between for(;;) and if (semid == -1) block, while it's trying to free its last sem_undo structure which has already been freed by freeary(). Each sem_undo struct is on two lists: one per semaphore set (list_id) and one per process (list_proc). The list_id list tracks undos by semaphore set, and the list_proc by process. Undo structures are removed either by freeary() or by exit_sem(). The freeary function is invoked when the user invokes a syscall to remove a semaphore set. During this operation freeary() traverses the list_id associated with the semaphore set and removes the undo structures from both the list_id and list_proc lists. For this case, exit_sem() is called at process exit. Each process contains a struct sem_undo_list (referred to as "ulp") which contains the head for the list_proc list. When the process exits, exit_sem() traverses this list to remove each sem_undo struct. As in freeary(), whenever a sem_undo struct is removed from list_proc, it is also removed from the list_id list. Removing elements from list_id is safe for both exit_sem() and freeary() due to sem_lock(). Removing elements from list_proc is not safe; freeary() locks &un->ulp->lock when it performs list_del_rcu(&un->list_proc) but exit_sem() does not (locking was removed by commit a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()"). This can result in the following situation while executing the reproducer [1] : Consider a child process in exit_sem() and the parent in freeary() (because of semctl(sid[i], NSEM, IPC_RMID)). - The list_proc for the child contains the last two undo structs A and B (the rest have been removed either by exit_sem() or freeary()). - The semid for A is 1 and semid for B is 2. - exit_sem() removes A and at the same time freeary() removes B. - Since A and B have different semid sem_lock() will acquire different locks for each process and both can proceed. The bug is that they remove A and B from the same list_proc at the same time because only freeary() acquires the ulp lock. When exit_sem() removes A it makes ulp->list_proc.next to point at B and at the same time freeary() removes B setting B->semid=-1. At the next iteration of for(;;) loop exit_sem() will try to remove B. The only way to break from for(;;) is for (&un->list_proc == &ulp->list_proc) to be true which is not. Then exit_sem() will check if B->semid=-1 which is and will continue looping in for(;;) until the memory for B is reallocated and the value at B->semid is changed. At that point, exit_sem() will crash attempting to unlink B from the lists (this can be easily triggered by running the reproducer [1] a second time). To prove this scenario instrumentation was added to keep information about each sem_undo (un) struct that is removed per process and per semaphore set (sma). CPU0 CPU1 [caller holds sem_lock(sma for A)] ... freeary() exit_sem() ... ... ... sem_lock(sma for B) spin_lock(A->ulp->lock) ... list_del_rcu(un_A->list_proc) list_del_rcu(un_B->list_proc) Undo structures A and B have different semid and sem_lock() operations proceed. However they belong to the same list_proc list and they are removed at the same time. This results into ulp->list_proc.next pointing to the address of B which is already removed. After reverting commit a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()") the issue was no longer reproducible. [1] https://bugzilla.redhat.com/show_bug.cgi?id=1694779 Link: http://lkml.kernel.org/r/20191211191318.11860-1-ioanna-maria.alifieraki@canonical.com Fixes: a97955844807 ("ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()") Signed-off-by: Ioanna Alifieraki Acked-by: Manfred Spraul Acked-by: Herton R. Krzesinski Cc: Arnd Bergmann Cc: Catalin Marinas Cc: Cc: Joel Fernandes (Google) Cc: Davidlohr Bueso Cc: Jay Vosburgh Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

ipc/sem.c: convert to use built-in RCU list checking

2019-09-26T00:51:41Z

CONFIG_PROVE_RCU_LIST requires list_for_each_entry_rcu() to pass a lockdep expression if using srcu or locking for protection. It can only check regular RCU protection, all other protection needs to be passed as lockdep expression. Link: http://lkml.kernel.org/r/20190830231817.76862-2-joel@joelfernandes.org Signed-off-by: Joel Fernandes (Google) Cc: Arnd Bergmann Cc: Bjorn Helgaas Cc: Catalin Marinas Cc: "Gustavo A. R. Silva" Cc: Jonathan Derrick Cc: Keith Busch Cc: Lorenzo Pieralisi Cc: "Paul E. McKenney" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc/sem.c: replace kvmalloc/memset with kvzalloc and use struct_size

2019-03-08T02:32:02Z

Use kvzalloc() instead of kvmalloc() and memset(). Also, make use of the struct_size() helper instead of the open-coded version in order to avoid any potential type mistakes. This code was detected with the help of Coccinelle. Link: http://lkml.kernel.org/r/20190131214221.GA28930@embeddedor Signed-off-by: Gustavo A. R. Silva Reviewed-by: Andrew Morton Cc: Davidlohr Bueso Cc: Manfred Spraul Cc: Kees Cook Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: annotate implicit fall through

2019-03-08T02:32:02Z

There is a plan to build the kernel with -Wimplicit-fallthrough and this place in the code produced a warning (W=1). This commit remove the following warning: ipc/sem.c:1683:6: warning: this statement may fall through [-Wimplicit-fallthrough=] Link: http://lkml.kernel.org/r/20190114203608.18218-1-malat@debian.org Signed-off-by: Mathieu Malaterre Reviewed-by: Andrew Morton Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

y2038: syscalls: rename y2038 compat syscalls

2019-02-06T23:13:27Z

A lot of system calls that pass a time_t somewhere have an implementation using a COMPAT_SYSCALL_DEFINEx() on 64-bit architectures, and have been reworked so that this implementation can now be used on 32-bit architectures as well. The missing step is to redefine them using the regular SYSCALL_DEFINEx() to get them out of the compat namespace and make it possible to build them on 32-bit architectures. Any system call that ends in 'time' gets a '32' suffix on its name for that version, while the others get a '_time32' suffix, to distinguish them from the normal version, which takes a 64-bit time argument in the future. In this step, only 64-bit architectures are changed, doing this rename first lets us avoid touching the 32-bit architectures twice. Acked-by: Catalin Marinas Signed-off-by: Arnd Bergmann

ipc: rename old-style shmctl/semctl/msgctl syscalls

2019-01-25T16:22:50Z

The behavior of these system calls is slightly different between architectures, as determined by the CONFIG_ARCH_WANT_IPC_PARSE_VERSION symbol. Most architectures that implement the split IPC syscalls don't set that symbol and only get the modern version, but alpha, arm, microblaze, mips-n32, mips-n64 and xtensa expect the caller to pass the IPC_64 flag. For the architectures that so far only implement sys_ipc(), i.e. m68k, mips-o32, powerpc, s390, sh, sparc, and x86-32, we want the new behavior when adding the split syscalls, so we need to distinguish between the two groups of architectures. The method I picked for this distinction is to have a separate system call entry point: sys_old_*ctl() now uses ipc_parse_version, while sys_*ctl() does not. The system call tables of the five architectures are changed accordingly. As an additional benefit, we no longer need the configuration specific definition for ipc_parse_version(), it always does the same thing now, but simply won't get called on architectures with the modern interface. A small downside is that on architectures that do set ARCH_WANT_IPC_PARSE_VERSION, we now have an extra set of entry points that are never called. They only add a few bytes of bloat, so it seems better to keep them compared to adding yet another Kconfig symbol. I considered adding new syscall numbers for the IPC_64 variants for consistency, but decided against that for now. Signed-off-by: Arnd Bergmann

y2038: globally rename compat_time to old_time32

2018-08-27T12:48:48Z

Christoph Hellwig suggested a slightly different path for handling backwards compatibility with the 32-bit time_t based system calls: Rather than simply reusing the compat_sys_* entry points on 32-bit architectures unchanged, we get rid of those entry points and the compat_time types by renaming them to something that makes more sense on 32-bit architectures (which don't have a compat mode otherwise), and then share the entry points under the new name with the 64-bit architectures that use them for implementing the compatibility. The following types and interfaces are renamed here, and moved from linux/compat_time.h to linux/time32.h: old new --- --- compat_time_t old_time32_t struct compat_timeval struct old_timeval32 struct compat_timespec struct old_timespec32 struct compat_itimerspec struct old_itimerspec32 ns_to_compat_timeval() ns_to_old_timeval32() get_compat_itimerspec64() get_old_itimerspec32() put_compat_itimerspec64() put_old_itimerspec32() compat_get_timespec64() get_old_timespec32() compat_put_timespec64() put_old_timespec32() As we already have aliases in place, this patch addresses only the instances that are relevant to the system call interface in particular, not those that occur in device drivers and other modules. Those will get handled separately, while providing the 64-bit version of the respective interfaces. I'm not renaming the timex, rusage and itimerval structures, as we are still debating what the new interface will look like, and whether we will need a replacement at all. This also doesn't change the names of the syscall entry points, which can be done more easily when we actually switch over the 32-bit architectures to use them, at that point we need to change COMPAT_SYSCALL_DEFINEx to SYSCALL_DEFINEx with a new name, e.g. with a _time32 suffix. Suggested-by: Christoph Hellwig Link: https://lore.kernel.org/lkml/20180705222110.GA5698@infradead.org/ Signed-off-by: Arnd Bergmann

ipc/util.c: further variable name cleanups

2018-08-22T17:52:52Z

The varable names got a mess, thus standardize them again: id: user space id. Called semid, shmid, msgid if the type is known. Most functions use "id" already. idx: "index" for the idr lookup Right now, some functions use lid, ipc_addid() already uses idx as the variable name. seq: sequence number, to avoid quick collisions of the user space id key: user space key, used for the rhash tree Link: http://lkml.kernel.org/r/20180712185241.4017-12-manfred@colorfullife.com Signed-off-by: Manfred Spraul Cc: Dmitry Vyukov Cc: Davidlohr Bueso Cc: Davidlohr Bueso Cc: Herbert Xu Cc: Kees Cook Cc: Michael Kerrisk Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: simplify ipc initialization

2018-08-22T17:52:52Z

Now that we know that rhashtable_init() will not fail, we can get rid of a lot of the unnecessary cleanup paths when the call errored out. [manfred@colorfullife.com: variable name added to util.h to resolve checkpatch warning] Link: http://lkml.kernel.org/r/20180712185241.4017-11-manfred@colorfullife.com Signed-off-by: Davidlohr Bueso Signed-off-by: Manfred Spraul Cc: Dmitry Vyukov Cc: Herbert Xu Cc: Kees Cook Cc: Michael Kerrisk Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: rename ipcctl_pre_down_nolock()

2018-08-22T17:52:51Z

Both the comment and the name of ipcctl_pre_down_nolock() are misleading: The function must be called while holdling the rw semaphore. Therefore the patch renames the function to ipcctl_obtain_check(): This name matches the other names used in util.c: - "obtain" function look up a pointer in the idr, without acquiring the object lock. - The caller is responsible for locking. - _check means that the sequence number is checked. Link: http://lkml.kernel.org/r/20180712185241.4017-5-manfred@colorfullife.com Signed-off-by: Manfred Spraul Reviewed-by: Davidlohr Bueso Cc: Davidlohr Bueso Cc: Dmitry Vyukov Cc: Herbert Xu Cc: Kees Cook Cc: Michael Kerrisk Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds