Commit 62133cb1 authored by Ulrich Drepper's avatar Ulrich Drepper Committed by Steve French

[PATCH] tgkill patch for safe inter-thread signals

This is the updated versions of the patch Ingo sent some time ago to
implement a new tgkill() syscall which specifies the target thread
without any possibility of ambiguity or thread ID wrap races, by passing
in both the thread group _and_ the thread ID as the arguments.

This is really needed since many/most people still run with limited PID
ranges (maybe due to legacy apps breaking) and the PID reuse can cause
problems.
parent f597d1de
......@@ -876,5 +876,6 @@ ENTRY(sys_call_table)
.long sys_clock_nanosleep
.long sys_statfs64
.long sys_fstatfs64
.long sys_tgkill
nr_syscalls=(.-sys_call_table)/4
......@@ -275,8 +275,9 @@
#define __NR_clock_nanosleep (__NR_timer_create+8)
#define __NR_statfs64 268
#define __NR_fstatfs64 269
#define __NR_tgkill 270
#define NR_syscalls 270
#define NR_syscalls 271
/* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */
......
......@@ -579,8 +579,8 @@ static int rm_from_queue(unsigned long mask, struct sigpending *s)
/*
* Bad permissions for sending the signal
*/
static inline int check_kill_permission(int sig, struct siginfo *info,
struct task_struct *t)
static int check_kill_permission(int sig, struct siginfo *info,
struct task_struct *t)
{
int error = -EINVAL;
if (sig < 0 || sig > _NSIG)
......@@ -2088,6 +2088,52 @@ sys_kill(int pid, int sig)
return kill_something_info(sig, &info, pid);
}
/**
* sys_tkill - send signal to one specific thread
* @tgid: the thread group ID of the thread
* @pid: the PID of the thread
* @sig: signal to be sent
*
* This syscall also checks the tgid and returns -ESRCH even if the PID
* exists but it's not belonging to the target process anymore. This
* method solves the problem of threads exiting and PIDs getting reused.
*/
asmlinkage long sys_tgkill(int tgid, int pid, int sig)
{
struct siginfo info;
int error;
struct task_struct *p;
/* This is only valid for single tasks */
if (pid <= 0 || tgid <= 0)
return -EINVAL;
info.si_signo = sig;
info.si_errno = 0;
info.si_code = SI_TKILL;
info.si_pid = current->tgid;
info.si_uid = current->uid;
read_lock(&tasklist_lock);
p = find_task_by_pid(pid);
error = -ESRCH;
if (p && (p->tgid == tgid)) {
error = check_kill_permission(sig, &info, p);
/*
* The null signal is a permissions and process existence
* probe. No signal is actually delivered.
*/
if (!error && sig && p->sighand) {
spin_lock_irq(&p->sighand->siglock);
handle_stop_signal(sig, p);
error = specific_send_sig_info(sig, &info, p);
spin_unlock_irq(&p->sighand->siglock);
}
}
read_unlock(&tasklist_lock);
return error;
}
/*
* Send a signal to only one task, even if it's a CLONE_THREAD task.
*/
......
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