[PATCH] tty: ->signal->tty locking

Fix the locking of signal->tty.

Use ->sighand->siglock to protect ->signal->tty; this lock is already used
by most other members of ->signal/->sighand.  And unless we are 'current'
or the tasklist_lock is held we need ->siglock to access ->signal anyway.

(NOTE: sys_unshare() is broken wrt ->sighand locking rules)

Note that tty_mutex is held over tty destruction, so while holding
tty_mutex any tty pointer remains valid.  Otherwise the lifetime of ttys
are governed by their open file handles.  This leaves some holes for tty
access from signal->tty (or any other non file related tty access).

It solves the tty SLAB scribbles we were seeing.

(NOTE: the change from group_send_sig_info to __group_send_sig_info needs to
       be examined by someone familiar with the security framework, I think
       it is safe given the SEND_SIG_PRIV from other __group_send_sig_info
       invocations)

[schwidefsky@de.ibm.com: 3270 fix]
[akpm@osdl.org: various post-viro fixes]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Alan Cox <alan@redhat.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Cc: Roland McGrath <roland@redhat.com>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Cc: James Morris <jmorris@namei.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Jan Kara <jack@ucw.cz>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/arch/um/kernel/exec.c b/arch/um/kernel/exec.c
index 0561c43b4685..8d56ec6cca79 100644
--- a/arch/um/kernel/exec.c
+++ b/arch/um/kernel/exec.c
@@ -39,12 +39,13 @@ static long execve1(char *file, char __user * __user *argv,
                     char __user *__user *env)
 {
         long error;
+        struct tty_struct *tty;
 
 #ifdef CONFIG_TTY_LOG
         mutex_lock(&tty_mutex);
-        task_lock(current);     /* FIXME:  is this needed ? */
-        log_exec(argv, current->signal->tty);
-        task_unlock(current);
+        tty = get_current_tty();
+        if (tty)
+                log_exec(argv, tty);
         mutex_unlock(&tty_mutex);
 #endif
         error = do_execve(file, argv, env, &current->thread.regs);