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rlimits: allow setrlimit to non-current tasks 

Add locking to allow setrlimit accept task parameter other than
current.

Namely, lock tasklist_lock for read and check whether the task
structure has sighand non-null. Do all the signal processing under
that lock still held.

There are some points:
1) security_task_setrlimit is now called with that lock held. This is
   not new, many security_* functions are called with this lock held
   already so it doesn't harm (all this security_* stuff does almost
   the same).
2) task->sighand->siglock (in update_rlimit_cpu) is nested in
   tasklist_lock. This dependence is already existing.
3) tsk->alloc_lock is nested in tasklist_lock. This is OK too, already
   existing dependence.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
This commit is contained in:
Jiri Slaby 2009-08-28 14:08:17 +02:00
parent 7855c35da7
commit 1c1e618ddd
1 changed files with 10 additions and 1 deletions
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11
kernel/sys.c
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@ -1272,6 +1272,7 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
#endif
/* make sure you are allowed to change @tsk limits before calling this */
int do_setrlimit(struct task_struct *tsk, unsigned int resource,
struct rlimit *new_rlim)
{
@ -1285,9 +1286,16 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
return -EPERM;
/* protect tsk->signal and tsk->sighand from disappearing */
read_lock(&tasklist_lock);
if (!tsk->sighand) {
retval = -ESRCH;
goto out;
}
retval = security_task_setrlimit(tsk->group_leader, resource, new_rlim);
if (retval)
return retval;
goto out;
if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
/*
@ -1322,6 +1330,7 @@ int do_setrlimit(struct task_struct *tsk, unsigned int resource,
update_rlimit_cpu(tsk, new_rlim->rlim_cur);
out:
read_unlock(&tasklist_lock);
return retval;
}