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[PATCH] fork: fix race in setting child's pgrp and tty

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In fork, child should recopy parent's pgrp/tty after it has tasklist_lock.
Otherwise following a setpgid() on the parent, *after* copy_signal(), the
child will own a stale pgrp (which may be reused); (eg.  if copy_mm()
sleeps a long while due to memory pressure).  Similar issue for the tty.

Signed-off-by: Oren Laadan <orenl@cs.columbia.edu>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oren Laadan 2006-01-08 01:03:51 -08:00 committed by Linus Torvalds
parent fb86a35b9d
commit 9a5d3023e6
1 changed files with 3 additions and 6 deletions
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9
kernel/fork.c
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@ -811,9 +811,6 @@ static inline int copy_signal(unsigned long clone_flags, struct task_struct * ts
sig->it_prof_expires = cputime_zero; sig->it_prof_expires = cputime_zero;
sig->it_prof_incr = cputime_zero; sig->it_prof_incr = cputime_zero;
sig->tty = current->signal->tty;
sig->pgrp = process_group(current);
sig->session = current->signal->session;
sig->leader = 0; /* session leadership doesn't inherit */ sig->leader = 0; /* session leadership doesn't inherit */
sig->tty_old_pgrp = 0; sig->tty_old_pgrp = 0;
@ -1136,15 +1133,15 @@ static task_t *copy_process(unsigned long clone_flags,
attach_pid(p, PIDTYPE_PID, p->pid); attach_pid(p, PIDTYPE_PID, p->pid);
attach_pid(p, PIDTYPE_TGID, p->tgid); attach_pid(p, PIDTYPE_TGID, p->tgid);
if (thread_group_leader(p)) { if (thread_group_leader(p)) {
p->signal->tty = current->signal->tty;
p->signal->pgrp = process_group(current);
p->signal->session = current->signal->session;
attach_pid(p, PIDTYPE_PGID, process_group(p)); attach_pid(p, PIDTYPE_PGID, process_group(p));
attach_pid(p, PIDTYPE_SID, p->signal->session); attach_pid(p, PIDTYPE_SID, p->signal->session);
if (p->pid) if (p->pid)
__get_cpu_var(process_counts)++; __get_cpu_var(process_counts)++;
} }
if (!current->signal->tty && p->signal->tty)
p->signal->tty = NULL;
nr_threads++; nr_threads++;
total_forks++; total_forks++;
write_unlock_irq(&tasklist_lock); write_unlock_irq(&tasklist_lock);