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tty: audit: Simplify first-use allocation 

The first-use tty audit buffer allocation is a potential race
amongst multiple attempts at 'first-use'; only one 'winner' is
acceptable.

The successful buffer assignment occurs if tty_audit_buf == NULL
(which will also be the return from cmpxchg()); otherwise, another
racer 'won' and this buffer allocation is freed.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Peter Hurley 2016-01-09 22:55:36 -08:00 committed by Greg Kroah-Hartman
parent 5493090fc2
commit fbaa122718
1 changed files with 7 additions and 15 deletions
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22
drivers/tty/tty_audit.c
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@ -181,30 +181,22 @@ int tty_audit_push(void)
*/
static struct tty_audit_buf *tty_audit_buf_get(void)
{
struct tty_audit_buf *buf, *buf2;
unsigned long flags;
struct tty_audit_buf *buf;
buf = current->signal->tty_audit_buf;
if (buf)
return buf;
buf2 = tty_audit_buf_alloc();
if (buf2 == NULL) {
buf = tty_audit_buf_alloc();
if (buf == NULL) {
audit_log_lost("out of memory in TTY auditing");
return NULL;
}
spin_lock_irqsave(&current->sighand->siglock, flags);
buf = current->signal->tty_audit_buf;
if (!buf) {
current->signal->tty_audit_buf = buf2;
buf = buf2;
buf2 = NULL;
}
spin_unlock_irqrestore(&current->sighand->siglock, flags);
if (buf2)
tty_audit_buf_free(buf2);
return buf;
/* Race to use this buffer, free it if another wins */
if (cmpxchg(&current->signal->tty_audit_buf, NULL, buf) != NULL)
tty_audit_buf_free(buf);
return current->signal->tty_audit_buf;
}
/**