Commit b0d62e6d authored by Jason Baron's avatar Jason Baron Committed by Linus Torvalds
Browse files

[PATCH] fix disassociate_ctty vs. fork race



Race is as follows. Process A forks process B, both being part of the same
session. Then, A calls disassociate_ctty while B forks C:

A				B
====				====
				fork()
				  copy_signal()
dissasociate_ctty()		....
				  attach_pid(p, PIDTYPE_SID, p->signal->session);

Now, C can have current->signal->tty pointing to a freed tty structure, as
it hasn't yet been added to the session group (to have its controlling tty
cleared on the diassociate_ctty() call).

This has shown up as an oops but could be even more serious.  I haven't
tried to create a test case, but a customer has verified that the patch
below resolves the issue, which was occuring quite frequently.  I'll try
and post the test case if i can.

The patch simply checks for a NULL tty *after* it has been attached to the
proper session group and clears it as necessary.  Alternatively, we could
simply do the tty assignment after the the process is added to the proper
session group.
Signed-off-by: default avatarJason Baron <jbaron@redhat.com>
Cc: Roland McGrath <roland@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent f76baf93
......@@ -1116,6 +1116,9 @@ static task_t *copy_process(unsigned long clone_flags,
__get_cpu_var(process_counts)++;
}
if (!current->signal->tty && p->signal->tty)
p->signal->tty = NULL;
nr_threads++;
total_forks++;
write_unlock_irq(&tasklist_lock);
......
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