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Subject[patch] More ptrace fixes for 2.5.33
Ingo,

Thanks for your collected resync patch this morning. Here are the changes I
have on top of BK-curr + that patch:

- Fix some bugs I introduced in zap_thread
- Improve the check for traced children in sys_wait4
- Fix parent links when using CLONE_PTRACE

(My thanks to OGAWA Hirofumi for pointing out the first bit.) Are the wait4
changes about what you had in mind?


The only other issue I know of is something else Hirofumi pointed out
earlier; there are problems when a tracing process dies unexpectedly. I'll
come back to that later.

diff -up -r /big/kernel/linux-2.5/kernel/exit.c /big/kernel/linux-2.5-fixes/kernel/exit.c
--- linux-2.5/kernel/exit.c 2002-09-06 14:16:06.000000000 -0400
+++ linux-2.5-fixes/kernel/exit.c 2002-09-06 14:14:32.000000000 -0400
@@ -449,15 +449,19 @@ static inline void forget_original_paren

static inline void zap_thread(task_t *p, task_t *father, int traced)
{
- /* If we were tracing the thread, release it; otherwise preserve the
- ptrace links. */
+ /* If someone else is tracing this thread, preserve the ptrace links. */
if (unlikely(traced)) {
task_t *trace_task = p->parent;
+ int ptrace_flag = p->ptrace;
+ BUG_ON (ptrace_flag == 0);
+
__ptrace_unlink(p);
- p->ptrace = 1;
+ p->ptrace = ptrace_flag;
__ptrace_link(p, trace_task);
} else {
- p->ptrace = 0;
+ /* Otherwise, if we were tracing this thread, untrace it. */
+ ptrace_unlink (p);
+
list_del_init(&p->sibling);
p->parent = p->real_parent;
list_add_tail(&p->sibling, &p->parent->children);
@@ -646,6 +650,41 @@ asmlinkage long sys_exit(int error_code)
do_exit((error_code&0xff)<<8);
}

+static inline int eligible_child(pid_t pid, int options, task_t *p)
+{
+ if (pid>0) {
+ if (p->pid != pid)
+ return 0;
+ } else if (!pid) {
+ if (p->pgrp != current->pgrp)
+ return 0;
+ } else if (pid != -1) {
+ if (p->pgrp != -pid)
+ return 0;
+ }
+
+ /*
+ * Do not consider detached threads that are
+ * not ptraced:
+ */
+ if (p->exit_signal == -1 && !p->ptrace)
+ return 0;
+
+ /* Wait for all children (clone and not) if __WALL is set;
+ * otherwise, wait for clone children *only* if __WCLONE is
+ * set; otherwise, wait for non-clone children *only*. (Note:
+ * A "clone" child here is one that reports to its parent
+ * using a signal other than SIGCHLD.) */
+ if (((p->exit_signal != SIGCHLD) ^ ((options & __WCLONE) != 0))
+ && !(options & __WALL))
+ return 0;
+
+ if (security_ops->task_wait(p))
+ return 0;
+
+ return 1;
+}
+
asmlinkage long sys_wait4(pid_t pid,unsigned int * stat_addr, int options, struct rusage * ru)
{
int flag, retval;
@@ -666,34 +705,8 @@ repeat:
struct list_head *_p;
list_for_each(_p,&tsk->children) {
p = list_entry(_p,struct task_struct,sibling);
- if (pid>0) {
- if (p->pid != pid)
- continue;
- } else if (!pid) {
- if (p->pgrp != current->pgrp)
- continue;
- } else if (pid != -1) {
- if (p->pgrp != -pid)
- continue;
- }
- /*
- * Do not consider detached threads that are
- * not ptraced:
- */
- if (p->exit_signal == -1 && !p->ptrace)
- continue;
- /* Wait for all children (clone and not) if __WALL is set;
- * otherwise, wait for clone children *only* if __WCLONE is
- * set; otherwise, wait for non-clone children *only*. (Note:
- * A "clone" child here is one that reports to its parent
- * using a signal other than SIGCHLD.) */
- if (((p->exit_signal != SIGCHLD) ^ ((options & __WCLONE) != 0))
- && !(options & __WALL))
+ if (!eligible_child(pid, options, p))
continue;
-
- if (security_ops->task_wait(p))
- continue;
-
flag = 1;
switch (p->state) {
case TASK_STOPPED:
@@ -738,12 +751,21 @@ repeat:
continue;
}
}
+ if (!flag) {
+ list_for_each (_p,&tsk->ptrace_children) {
+ p = list_entry(_p,struct task_struct,ptrace_list);
+ if (!eligible_child(pid, options, p))
+ continue;
+ flag = 1;
+ break;
+ }
+ }
if (options & __WNOTHREAD)
break;
tsk = next_thread(tsk);
} while (tsk != current);
read_unlock(&tasklist_lock);
- if (flag || !list_empty(&current->ptrace_children)) {
+ if (flag) {
retval = 0;
if (options & WNOHANG)
goto end_wait4;
diff -up -r -x setup -x bzImage -x bvmlinux -x '*.bin*' -x '*.a' -x '*.o' -x '.*' -x .config -x .config.old -x vmlinux -x System.map -x BitKeeper -x ChangeSet -x SCCS /big/kernel/linux-2.5/kernel/fork.c /big/kernel/linux-2.5-fixes/kernel/fork.c
--- /big/kernel/linux-2.5/kernel/fork.c 2002-09-05 17:09:41.000000000 -0400
+++ /big/kernel/linux-2.5-fixes/kernel/fork.c 2002-09-06 14:14:32.000000000 -0400
@@ -836,13 +836,11 @@ static struct task_struct *copy_process(
write_lock_irq(&tasklist_lock);

/* CLONE_PARENT re-uses the old parent */
- p->real_parent = current->real_parent;
- p->parent = current->parent;
- if (!(clone_flags & CLONE_PARENT)) {
+ if (clone_flags & CLONE_PARENT)
+ p->real_parent = current->real_parent;
+ else
p->real_parent = current;
- if (!(p->ptrace & PT_PTRACED))
- p->parent = current;
- }
+ p->parent = p->real_parent;

if (clone_flags & CLONE_THREAD) {
p->tgid = current->tgid;
@@ -850,7 +848,8 @@ static struct task_struct *copy_process(
}

SET_LINKS(p);
- ptrace_link(p, p->parent);
+ if (p->ptrace & PT_PTRACED)
+ __ptrace_link(p, current->parent);
hash_pid(p);
nr_threads++;
write_unlock_irq(&tasklist_lock);
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer
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