linux/fs/exec.c, branch v5.11

Merge branch 'parisc-5.11-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux

2020-12-16T20:10:40Z

Pull parisc updates from Helge Deller: "A change to increase the default maximum stack size on parisc to 100MB and the ability to further increase the stack hard limit size at runtime with ulimit for newly started processes. The other patches fix compile warnings, utilize the Kbuild logic and cleanups the parisc arch code" * 'parisc-5.11-1' of git://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux: parisc: pci-dma: fix warning unused-function parisc/uapi: Use Kbuild logic to provide parisc: Make user stack size configurable parisc: Use _TIF_USER_WORK_MASK in entry.S parisc: Drop loops_per_jiffy from per_cpu struct

Merge branch 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2020-12-16T03:36:48Z

Pull exec-update-lock update from Eric Biederman: "The key point of this is to transform exec_update_mutex into a rw_semaphore so readers can be separated from writers. This makes it easier to understand what the holders of the lock are doing, and makes it harder to contend or deadlock on the lock. The real deadlock fix wound up in perf_event_open" * 'exec-update-lock-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: exec: Transform exec_update_mutex into a rw_semaphore

Merge branch 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace

2020-12-16T03:29:43Z

Pull execve updates from Eric Biederman: "This set of changes ultimately fixes the interaction of posix file lock and exec. Fundamentally most of the change is just moving where unshare_files is called during exec, and tweaking the users of files_struct so that the count of files_struct is not unnecessarily played with. Along the way fcheck and related helpers were renamed to more accurately reflect what they do. There were also many other small changes that fell out, as this is the first time in a long time much of this code has been touched. Benchmarks haven't turned up any practical issues but Al Viro has observed a possibility for a lot of pounding on task_lock. So I have some changes in progress to convert put_files_struct to always rcu free files_struct. That wasn't ready for the merge window so that will have to wait until next time" * 'exec-for-v5.11' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (27 commits) exec: Move io_uring_task_cancel after the point of no return coredump: Document coredump code exclusively used by cell spufs file: Remove get_files_struct file: Rename __close_fd_get_file close_fd_get_file file: Replace ksys_close with close_fd file: Rename __close_fd to close_fd and remove the files parameter file: Merge __alloc_fd into alloc_fd file: In f_dupfd read RLIMIT_NOFILE once. file: Merge __fd_install into fd_install proc/fd: In fdinfo seq_show don't use get_files_struct bpf/task_iter: In task_file_seq_get_next use task_lookup_next_fd_rcu proc/fd: In proc_readfd_common use task_lookup_next_fd_rcu file: Implement task_lookup_next_fd_rcu kcmp: In get_file_raw_ptr use task_lookup_fd_rcu proc/fd: In tid_fd_mode use task_lookup_fd_rcu file: Implement task_lookup_fd_rcu file: Rename fcheck lookup_fd_rcu file: Replace fcheck_files with files_lookup_fd_rcu file: Factor files_lookup_fd_locked out of fcheck_files file: Rename __fcheck_files to files_lookup_fd_raw ...

exec: Transform exec_update_mutex into a rw_semaphore

2020-12-10T19:13:32Z

Recently syzbot reported[0] that there is a deadlock amongst the users of exec_update_mutex. The problematic lock ordering found by lockdep was: perf_event_open (exec_update_mutex -> ovl_i_mutex) chown (ovl_i_mutex -> sb_writes) sendfile (sb_writes -> p->lock) by reading from a proc file and writing to overlayfs proc_pid_syscall (p->lock -> exec_update_mutex) While looking at possible solutions it occured to me that all of the users and possible users involved only wanted to state of the given process to remain the same. They are all readers. The only writer is exec. There is no reason for readers to block on each other. So fix this deadlock by transforming exec_update_mutex into a rw_semaphore named exec_update_lock that only exec takes for writing. Cc: Jann Horn Cc: Vasiliy Kulikov Cc: Al Viro Cc: Bernd Edlinger Cc: Oleg Nesterov Cc: Christopher Yeoh Cc: Cyrill Gorcunov Cc: Sargun Dhillon Cc: Christian Brauner Cc: Arnd Bergmann Cc: Peter Zijlstra Cc: Ingo Molnar Cc: Arnaldo Carvalho de Melo Fixes: eea9673250db ("exec: Add exec_update_mutex to replace cred_guard_mutex") [0] https://lkml.kernel.org/r/00000000000063640c05ade8e3de@google.com Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com Link: https://lkml.kernel.org/r/87ft4mbqen.fsf@x220.int.ebiederm.org Signed-off-by: Eric W. Biederman

exec: Move io_uring_task_cancel after the point of no return

2020-12-10T18:57:13Z

Now that unshare_files happens in begin_new_exec after the point of no return, io_uring_task_cancel can also happen later. Effectively this means io_uring activities for a task are only canceled when exec succeeds. Link: https://lkml.kernel.org/r/878saih2op.fsf@x220.int.ebiederm.org Signed-off-by: Eric W. Biederman

exec: Simplify unshare_files

2020-12-10T18:39:32Z

Now that exec no longer needs to return the unshared files to their previous value there is no reason to return displaced. Instead when unshare_fd creates a copy of the file table, call put_files_struct before returning from unshare_files. Acked-by: Christian Brauner v1: https://lkml.kernel.org/r/20200817220425.9389-2-ebiederm@xmission.com Link: https://lkml.kernel.org/r/20201120231441.29911-2-ebiederm@xmission.com Signed-off-by: Eric W. Biederman

exec: Move unshare_files to fix posix file locking during exec

2020-12-10T18:39:24Z

Many moons ago the binfmts were doing some very questionable things with file descriptors and an unsharing of the file descriptor table was added to make things better[1][2]. The helper steal_lockss was added to avoid breaking the userspace programs[3][4][6]. Unfortunately it turned out that steal_locks did not work for network file systems[5], so it was removed to see if anyone would complain[7][8]. It was thought at the time that NPTL would not be affected as the unshare_files happened after the other threads were killed[8]. Unfortunately because there was an unshare_files in binfmt_elf.c before the threads were killed this analysis was incorrect. This unshare_files in binfmt_elf.c resulted in the unshares_files happening whenever threads were present. Which led to unshare_files being moved to the start of do_execve[9]. Later the problems were rediscovered and the suggested approach was to readd steal_locks under a different name[10]. I happened to be reviewing patches and I noticed that this approach was a step backwards[11]. I proposed simply moving unshare_files[12] and it was pointed out that moving unshare_files without auditing the code was also unsafe[13]. There were then several attempts to solve this[14][15][16] and I even posted this set of changes[17]. Unfortunately because auditing all of execve is time consuming this change did not make it in at the time. Well now that I am cleaning up exec I have made the time to read through all of the binfmts and the only playing with file descriptors is either the security modules closing them in security_bprm_committing_creds or is in the generic code in fs/exec.c. None of it happens before begin_new_exec is called. So move unshare_files into begin_new_exec, after the point of no return. If memory is very very very low and the application calling exec is sharing file descriptor tables between processes we might fail past the point of no return. Which is unfortunate but no different than any of the other places where we allocate memory after the point of no return. This movement allows another process that shares the file table, or another thread of the same process and that closes files or changes their close on exec behavior and races with execve to cause some unexpected things to happen. There is only one time of check to time of use race and it is just there so that execve fails instead of an interpreter failing when it tries to open the file it is supposed to be interpreting. Failing later if userspace is being silly is not a problem. With this change it the following discription from the removal of steal_locks[8] finally becomes true. Apps using NPTL are not affected, since all other threads are killed before execve. Apps using LinuxThreads are only affected if they - have multiple threads during exec (LinuxThreads doesn't kill other threads, the app may do it with pthread_kill_other_threads_np()) - rely on POSIX locks being inherited across exec Both conditions are documented, but not their interaction. Apps using clone() natively are affected if they - use clone(CLONE_FILES) - rely on POSIX locks being inherited across exec I have investigated some paths to make it possible to solve this without moving unshare_files but they all look more complicated[18]. Reported-by: Daniel P. Berrangé Reported-by: Jeff Layton History-tree: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git [1] 02cda956de0b ("[PATCH] unshare_files" [2] 04e9bcb4d106 ("[PATCH] use new unshare_files helper") [3] 088f5d7244de ("[PATCH] add steal_locks helper") [4] 02c541ec8ffa ("[PATCH] use new steal_locks helper") [5] https://lkml.kernel.org/r/E1FLIlF-0007zR-00@dorka.pomaz.szeredi.hu [6] https://lkml.kernel.org/r/0060321191605.GB15997@sorel.sous-sol.org [7] https://lkml.kernel.org/r/E1FLwjC-0000kJ-00@dorka.pomaz.szeredi.hu [8] c89681ed7d0e ("[PATCH] remove steal_locks()") [9] fd8328be874f ("[PATCH] sanitize handling of shared descriptor tables in failing execve()") [10] https://lkml.kernel.org/r/20180317142520.30520-1-jlayton@kernel.org [11] https://lkml.kernel.org/r/87r2nwqk73.fsf@xmission.com [12] https://lkml.kernel.org/r/87bmfgvg8w.fsf@xmission.com [13] https://lkml.kernel.org/r/20180322111424.GE30522@ZenIV.linux.org.uk [14] https://lkml.kernel.org/r/20180827174722.3723-1-jlayton@kernel.org [15] https://lkml.kernel.org/r/20180830172423.21964-1-jlayton@kernel.org [16] https://lkml.kernel.org/r/20180914105310.6454-1-jlayton@kernel.org [17] https://lkml.kernel.org/r/87a7ohs5ow.fsf@xmission.com [18] https://lkml.kernel.org/r/87pn8c1uj6.fsf_-_@x220.int.ebiederm.org Acked-by: Christian Brauner v1: https://lkml.kernel.org/r/20200817220425.9389-1-ebiederm@xmission.com Link: https://lkml.kernel.org/r/20201120231441.29911-1-ebiederm@xmission.com Signed-off-by: Eric W. Biederman

exec: Don't open code get_close_on_exec

2020-12-10T18:39:00Z

Al Viro pointed out that using the phrase "close_on_exec(fd, rcu_dereference_raw(current->files->fdt))" instead of wrapping it in rcu_read_lock(), rcu_read_unlock() is a very questionable optimization[1]. Once wrapped with rcu_read_lock()/rcu_read_unlock() that phrase becomes equivalent the helper function get_close_on_exec so simplify the code and make it more robust by simply using get_close_on_exec. [1] https://lkml.kernel.org/r/20201207222214.GA4115853@ZenIV.linux.org.uk Suggested-by: Al Viro Link: https://lkml.kernel.org/r/87k0tqr6zi.fsf_-_@x220.int.ebiederm.org Signed-off-by: Eric W. Biederman

kernel: Implement selective syscall userspace redirection

2020-12-02T14:07:56Z

Introduce a mechanism to quickly disable/enable syscall handling for a specific process and redirect to userspace via SIGSYS. This is useful for processes with parts that require syscall redirection and parts that don't, but who need to perform this boundary crossing really fast, without paying the cost of a system call to reconfigure syscall handling on each boundary transition. This is particularly important for Windows games running over Wine. The proposed interface looks like this: prctl(PR_SET_SYSCALL_USER_DISPATCH, , , , [selector]) The range [,+) is a part of the process memory map that is allowed to by-pass the redirection code and dispatch syscalls directly, such that in fast paths a process doesn't need to disable the trap nor the kernel has to check the selector. This is essential to return from SIGSYS to a blocked area without triggering another SIGSYS from rt_sigreturn. selector is an optional pointer to a char-sized userspace memory region that has a key switch for the mechanism. This key switch is set to either PR_SYS_DISPATCH_ON, PR_SYS_DISPATCH_OFF to enable and disable the redirection without calling the kernel. The feature is meant to be set per-thread and it is disabled on fork/clone/execv. Internally, this doesn't add overhead to the syscall hot path, and it requires very little per-architecture support. I avoided using seccomp, even though it duplicates some functionality, due to previous feedback that maybe it shouldn't mix with seccomp since it is not a security mechanism. And obviously, this should never be considered a security mechanism, since any part of the program can by-pass it by using the syscall dispatcher. For the sysinfo benchmark, which measures the overhead added to executing a native syscall that doesn't require interception, the overhead using only the direct dispatcher region to issue syscalls is pretty much irrelevant. The overhead of using the selector goes around 40ns for a native (unredirected) syscall in my system, and it is (as expected) dominated by the supervisor-mode user-address access. In fact, with SMAP off, the overhead is consistently less than 5ns on my test box. Signed-off-by: Gabriel Krisman Bertazi Signed-off-by: Thomas Gleixner Reviewed-by: Andy Lutomirski Acked-by: Peter Zijlstra (Intel) Acked-by: Kees Cook Link: https://lore.kernel.org/r/20201127193238.821364-4-krisman@collabora.com

parisc: Make user stack size configurable

2020-11-11T13:59:08Z

On parisc we need to initialize the memory layout for the user stack at process start time to a fixed size, which up until now was limited to the size as given by CONFIG_MAX_STACK_SIZE_MB at compile time. This hard limit was too small and showed problems when compiling ruby2.7, qmlcachegen and some Qt packages. This patch changes two things: a) It increases the default maximum stack size to 100MB. b) Users can modify the stack hard limit size with ulimit and then newly forked processes will use the given stack size which can even be bigger than the default 100MB. Reported-by: John David Anglin Signed-off-by: Helge Deller