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

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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)

[[email protected]: 3270 fix]
[[email protected]: various post-viro fixes]
Signed-off-by: Peter Zijlstra <[email protected]>
Acked-by: Alan Cox <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Prarit Bhargava <[email protected]>
Cc: Chris Wright <[email protected]>
Cc: Roland McGrath <[email protected]>
Cc: Stephen Smalley <[email protected]>
Cc: James Morris <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Jan Kara <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Peter Zijlstra 2006-12-08 02:36:04 -08:00 • committed by Linus Torvalds
commit 24ec839c43
12 changed files with 186 additions and 132 deletions
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9
kernel/acct.c
View file

@ -428,6 +428,7 @@ static void do_acct_process(struct file *file)
u64 elapsed;
u64 run_time;
struct timespec uptime;
struct tty_struct *tty;
/*
* First check to see if there is enough free_space to continue
@ -485,12 +486,8 @@ static void do_acct_process(struct file *file)
#endif
mutex_lock(&tty_mutex);
/* FIXME: Whoever is responsible for current->signal locking needs
to use the same locking all over the kernel and document it */
read_lock(&tasklist_lock);
ac.ac_tty = current->signal->tty ?
old_encode_dev(tty_devnum(current->signal->tty)) : 0;
read_unlock(&tasklist_lock);
tty = get_current_tty();
ac.ac_tty = tty ? old_encode_dev(tty_devnum(tty)) : 0;
mutex_unlock(&tty_mutex);
spin_lock_irq(&current->sighand->siglock);