This adds the pidfd_open() syscall. It allows a caller to retrieve pollable pidfds for a process which did not get created via CLONE_PIDFD, i.e. for a process that is created via traditional fork()/clone() calls that is only referenced by a PID:
int pidfd = pidfd_open(1234, 0); ret = pidfd_send_signal(pidfd, SIGSTOP, NULL, 0);
With the introduction of pidfds through CLONE_PIDFD it is possible to created pidfds at process creation time. However, a lot of processes get created with traditional PID-based calls such as fork() or clone() (without CLONE_PIDFD). For these processes a caller can currently not create a pollable pidfd. This is a huge problem for Android's low memory killer (LMK) and service managers such as systemd. Both are examples of tools that want to make use of pidfds to get reliable notification of process exit for non-parents (pidfd polling) and race-free signal sending (pidfd_send_signal()). They intend to switch to this API for process supervision/management as soon as possible. Having no way to get pollable pidfds from PID-only processes is one of the biggest blockers for them in adopting this api. With pidfd_open() making it possible to retrieve pidfd for PID-based processes we enable them to adopt this api.
In line with Arnd's recent changes to consolidate syscall numbers across architectures, I have added the pidfd_open() syscall to all architectures at the same time.
Signed-off-by: Christian Brauner christian@brauner.io Acked-by: Geert Uytterhoeven geert@linux-m68k.org Cc: Arnd Bergmann arnd@arndb.de Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Kees Cook keescook@chromium.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Jann Horn jannh@google.com Cc: David Howells dhowells@redhat.com Cc: Andy Lutomirsky luto@kernel.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Oleg Nesterov oleg@redhat.com Cc: Aleksa Sarai cyphar@cyphar.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Al Viro viro@zeniv.linux.org.uk Cc: linux-api@vger.kernel.org --- v1: - kbuild test robot lkp@intel.com: - add missing entry for pidfd_open to arch/arm/tools/syscall.tbl - Oleg Nesterov oleg@redhat.com: - use simpler thread-group leader check --- arch/alpha/kernel/syscalls/syscall.tbl | 1 + arch/arm/tools/syscall.tbl | 1 + arch/arm64/include/asm/unistd32.h | 2 + arch/ia64/kernel/syscalls/syscall.tbl | 1 + arch/m68k/kernel/syscalls/syscall.tbl | 1 + arch/microblaze/kernel/syscalls/syscall.tbl | 1 + arch/mips/kernel/syscalls/syscall_n32.tbl | 1 + arch/parisc/kernel/syscalls/syscall.tbl | 1 + arch/powerpc/kernel/syscalls/syscall.tbl | 1 + arch/s390/kernel/syscalls/syscall.tbl | 1 + arch/sh/kernel/syscalls/syscall.tbl | 1 + arch/sparc/kernel/syscalls/syscall.tbl | 1 + arch/x86/entry/syscalls/syscall_32.tbl | 1 + arch/x86/entry/syscalls/syscall_64.tbl | 1 + arch/xtensa/kernel/syscalls/syscall.tbl | 1 + include/linux/pid.h | 1 + include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 4 +- kernel/fork.c | 2 +- kernel/pid.c | 50 +++++++++++++++++++++ 20 files changed, 72 insertions(+), 2 deletions(-)
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl index 165f268beafc..ddc3c93ad7a7 100644 --- a/arch/alpha/kernel/syscalls/syscall.tbl +++ b/arch/alpha/kernel/syscalls/syscall.tbl @@ -467,3 +467,4 @@ 535 common io_uring_setup sys_io_uring_setup 536 common io_uring_enter sys_io_uring_enter 537 common io_uring_register sys_io_uring_register +538 common pidfd_open sys_pidfd_open diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl index 0393917eaa57..fc41fb34a636 100644 --- a/arch/arm/tools/syscall.tbl +++ b/arch/arm/tools/syscall.tbl @@ -441,3 +441,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h index 23f1a44acada..350e2049b4a9 100644 --- a/arch/arm64/include/asm/unistd32.h +++ b/arch/arm64/include/asm/unistd32.h @@ -874,6 +874,8 @@ __SYSCALL(__NR_io_uring_setup, sys_io_uring_setup) __SYSCALL(__NR_io_uring_enter, sys_io_uring_enter) #define __NR_io_uring_register 427 __SYSCALL(__NR_io_uring_register, sys_io_uring_register) +#define __NR_pidfd_open 428 +__SYSCALL(__NR_pidfd_open, sys_pidfd_open)
/* * Please add new compat syscalls above this comment and update diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl index 56e3d0b685e1..7115f6dd347a 100644 --- a/arch/ia64/kernel/syscalls/syscall.tbl +++ b/arch/ia64/kernel/syscalls/syscall.tbl @@ -348,3 +348,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl index df4ec3ec71d1..44bf12b16ffe 100644 --- a/arch/m68k/kernel/syscalls/syscall.tbl +++ b/arch/m68k/kernel/syscalls/syscall.tbl @@ -427,3 +427,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl index 4964947732af..0d32e5152dc0 100644 --- a/arch/microblaze/kernel/syscalls/syscall.tbl +++ b/arch/microblaze/kernel/syscalls/syscall.tbl @@ -433,3 +433,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl index 9392dfe33f97..726e107b3c9f 100644 --- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl @@ -366,3 +366,4 @@ 425 n32 io_uring_setup sys_io_uring_setup 426 n32 io_uring_enter sys_io_uring_enter 427 n32 io_uring_register sys_io_uring_register +428 n32 pidfd_open sys_pidfd_open diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl index fe8ca623add8..83b46b568d51 100644 --- a/arch/parisc/kernel/syscalls/syscall.tbl +++ b/arch/parisc/kernel/syscalls/syscall.tbl @@ -424,3 +424,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl index 00f5a63c8d9a..5294d04d7fa5 100644 --- a/arch/powerpc/kernel/syscalls/syscall.tbl +++ b/arch/powerpc/kernel/syscalls/syscall.tbl @@ -509,3 +509,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl index 061418f787c3..dcdb838adf49 100644 --- a/arch/s390/kernel/syscalls/syscall.tbl +++ b/arch/s390/kernel/syscalls/syscall.tbl @@ -430,3 +430,4 @@ 425 common io_uring_setup sys_io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open sys_pidfd_open diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl index 480b057556ee..8e66edfbc521 100644 --- a/arch/sh/kernel/syscalls/syscall.tbl +++ b/arch/sh/kernel/syscalls/syscall.tbl @@ -430,3 +430,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl index a1dd24307b00..d6f3bc686939 100644 --- a/arch/sparc/kernel/syscalls/syscall.tbl +++ b/arch/sparc/kernel/syscalls/syscall.tbl @@ -473,3 +473,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl index 4cd5f982b1e5..1af6b469160a 100644 --- a/arch/x86/entry/syscalls/syscall_32.tbl +++ b/arch/x86/entry/syscalls/syscall_32.tbl @@ -438,3 +438,4 @@ 425 i386 io_uring_setup sys_io_uring_setup __ia32_sys_io_uring_setup 426 i386 io_uring_enter sys_io_uring_enter __ia32_sys_io_uring_enter 427 i386 io_uring_register sys_io_uring_register __ia32_sys_io_uring_register +428 i386 pidfd_open sys_pidfd_open __ia32_sys_pidfd_open diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index 64ca0d06259a..c18e6ebe3387 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -355,6 +355,7 @@ 425 common io_uring_setup __x64_sys_io_uring_setup 426 common io_uring_enter __x64_sys_io_uring_enter 427 common io_uring_register __x64_sys_io_uring_register +428 common pidfd_open __x64_sys_pidfd_open
# # x32-specific system call numbers start at 512 to avoid cache impact diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl index 30084eaf8422..21ee795f3003 100644 --- a/arch/xtensa/kernel/syscalls/syscall.tbl +++ b/arch/xtensa/kernel/syscalls/syscall.tbl @@ -398,3 +398,4 @@ 425 common io_uring_setup sys_io_uring_setup 426 common io_uring_enter sys_io_uring_enter 427 common io_uring_register sys_io_uring_register +428 common pidfd_open sys_pidfd_open diff --git a/include/linux/pid.h b/include/linux/pid.h index 3c8ef5a199ca..c938a92eab99 100644 --- a/include/linux/pid.h +++ b/include/linux/pid.h @@ -67,6 +67,7 @@ struct pid extern struct pid init_struct_pid;
extern const struct file_operations pidfd_fops; +extern int pidfd_create(struct pid *pid);
static inline struct pid *get_pid(struct pid *pid) { diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index e2870fe1be5b..989055e0b501 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -929,6 +929,7 @@ asmlinkage long sys_clock_adjtime32(clockid_t which_clock, struct old_timex32 __user *tx); asmlinkage long sys_syncfs(int fd); asmlinkage long sys_setns(int fd, int nstype); +asmlinkage long sys_pidfd_open(pid_t pid, unsigned int flags); asmlinkage long sys_sendmmsg(int fd, struct mmsghdr __user *msg, unsigned int vlen, unsigned flags); asmlinkage long sys_process_vm_readv(pid_t pid, diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index dee7292e1df6..94a257a93d20 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -832,9 +832,11 @@ __SYSCALL(__NR_io_uring_setup, sys_io_uring_setup) __SYSCALL(__NR_io_uring_enter, sys_io_uring_enter) #define __NR_io_uring_register 427 __SYSCALL(__NR_io_uring_register, sys_io_uring_register) +#define __NR_pidfd_open 428 +__SYSCALL(__NR_pidfd_open, sys_pidfd_open)
#undef __NR_syscalls -#define __NR_syscalls 428 +#define __NR_syscalls 429
/* * 32 bit systems traditionally used different diff --git a/kernel/fork.c b/kernel/fork.c index 737db1828437..980cc1d2b8d4 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1714,7 +1714,7 @@ const struct file_operations pidfd_fops = { * Return: On success, a cloexec pidfd is returned. * On error, a negative errno number will be returned. */ -static int pidfd_create(struct pid *pid) +int pidfd_create(struct pid *pid) { int fd;
diff --git a/kernel/pid.c b/kernel/pid.c index 20881598bdfa..4afca3d6dcb8 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -38,6 +38,7 @@ #include <linux/syscalls.h> #include <linux/proc_ns.h> #include <linux/proc_fs.h> +#include <linux/sched/signal.h> #include <linux/sched/task.h> #include <linux/idr.h>
@@ -451,6 +452,55 @@ struct pid *find_ge_pid(int nr, struct pid_namespace *ns) return idr_get_next(&ns->idr, &nr); }
+/** + * pidfd_open() - Open new pid file descriptor. + * + * @pid: pid for which to retrieve a pidfd + * @flags: flags to pass + * + * This creates a new pid file descriptor with the O_CLOEXEC flag set for + * the process identified by @pid. Currently, the process identified by + * @pid must be a thread-group leader. This restriction currently exists + * for all aspects of pidfds including pidfd creation (CLONE_PIDFD cannot + * be used with CLONE_THREAD) and pidfd polling (only supports thread group + * leaders). + * + * Return: On success, a cloexec pidfd is returned. + * On error, a negative errno number will be returned. + */ +SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags) +{ + int fd, ret; + struct pid *p; + struct task_struct *tsk; + + if (flags) + return -EINVAL; + + if (pid <= 0) + return -EINVAL; + + p = find_get_pid(pid); + if (!p) + return -ESRCH; + + ret = 0; + rcu_read_lock(); + /* + * If this returns non-NULL the pid was used as a thread-group + * leader. Note, we race with exec here: If it changes the + * thread-group leader we might return the old leader. + */ + tsk = pid_task(p, PIDTYPE_TGID); + if (!tsk) + ret = -ESRCH; + rcu_read_unlock(); + + fd = ret ?: pidfd_create(p); + put_pid(p); + return fd; +} + void __init pid_idr_init(void) { /* Verify no one has done anything silly: */