[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.

diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index 5aef7a47a38308dcb12b1c0f979a7b6a48bc7eea..dafcae8663c896f0ca4294d88df3e8b6b412deca 100644 (file)
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -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

diff --git a/include/asm-i386/unistd.h b/include/asm-i386/unistd.h
index b1bdc016eed50252a24799c968b35e669d44102d..f39e505e3eb4b71e21787e502d1aa55de15346bf 100644 (file)
--- a/include/asm-i386/unistd.h
+++ b/include/asm-i386/unistd.h
@@ -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> */
 

diff --git a/kernel/signal.c b/kernel/signal.c
index dbefbea7623e4eb3bb84219800256cfb1485c78a..7ac72191b30bf0e38bce5ceb99c1caf6d30af484 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -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.
  */