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authorJiri Slaby <jslaby@suse.cz>2010-11-29 10:16:54 +0100
committerGreg Kroah-Hartman <gregkh@suse.de>2010-11-29 14:52:48 -0800
commitacfa747baf73922021a047f2d87a2d866f5dbab5 (patch)
treef47037d4c02341a9e4102eddd7dc6c774e6b439d
parente2efafbf139d2bfdfe96f2901f03189fecd172e4 (diff)
TTY: open/hangup race fixup
Like in the "TTY: don't allow reopen when ldisc is changing" patch, this one fixes a TTY WARNING as described in the option 1) there: 1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this section tty_lock is held. However tty_lock is temporarily dropped in the middle of the function by tty_ldisc_hangup. The fix is to introduce a new flag which we set during the unlocked window and check it in tty_reopen too. The flag is TTY_HUPPING and is cleared after TTY_HUPPED is set. While at it, remove duplicate TTY_HUPPED set_bit. The one after calling ops->hangup seems to be more correct. But anyway, we hold tty_lock, so there should be no difference. Also document the function it does that kind of crap. Nicely reproducible with two forked children: static void do_work(const char *tty) { if (signal(SIGHUP, SIG_IGN) == SIG_ERR) exit(1); setsid(); while (1) { int fd = open(tty, O_RDWR|O_NOCTTY); if (fd < 0) continue; if (ioctl(fd, TIOCSCTTY)) continue; if (vhangup()) continue; close(fd); } exit(0); } Signed-off-by: Jiri Slaby <jslaby@suse.cz> Reported-by: <Valdis.Kletnieks@vt.edu> Reported-by: Kyle McMartin <kyle@mcmartin.ca> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: stable <stable@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/tty/tty_io.c10
-rw-r--r--include/linux/tty.h1
2 files changed, 10 insertions, 1 deletions
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 878f6d667b17..35480dd57a30 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -559,6 +559,9 @@ void __tty_hangup(struct tty_struct *tty)
tty_lock();
+ /* some functions below drop BTM, so we need this bit */
+ set_bit(TTY_HUPPING, &tty->flags);
+
/* inuse_filps is protected by the single tty lock,
this really needs to change if we want to flush the
workqueue with the lock held */
@@ -578,6 +581,10 @@ void __tty_hangup(struct tty_struct *tty)
}
spin_unlock(&tty_files_lock);
+ /*
+ * it drops BTM and thus races with reopen
+ * we protect the race by TTY_HUPPING
+ */
tty_ldisc_hangup(tty);
read_lock(&tasklist_lock);
@@ -615,7 +622,6 @@ void __tty_hangup(struct tty_struct *tty)
tty->session = NULL;
tty->pgrp = NULL;
tty->ctrl_status = 0;
- set_bit(TTY_HUPPED, &tty->flags);
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
/* Account for the p->signal references we killed */
@@ -641,6 +647,7 @@ void __tty_hangup(struct tty_struct *tty)
* can't yet guarantee all that.
*/
set_bit(TTY_HUPPED, &tty->flags);
+ clear_bit(TTY_HUPPING, &tty->flags);
tty_ldisc_enable(tty);
tty_unlock();
@@ -1311,6 +1318,7 @@ static int tty_reopen(struct tty_struct *tty)
struct tty_driver *driver = tty->driver;
if (test_bit(TTY_CLOSING, &tty->flags) ||
+ test_bit(TTY_HUPPING, &tty->flags) ||
test_bit(TTY_LDISC_CHANGING, &tty->flags))
return -EIO;
diff --git a/include/linux/tty.h b/include/linux/tty.h
index c7ea9bc8897c..021bfd2f0860 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -367,6 +367,7 @@ struct tty_file_private {
#define TTY_HUPPED 18 /* Post driver->hangup() */
#define TTY_FLUSHING 19 /* Flushing to ldisc in progress */
#define TTY_FLUSHPENDING 20 /* Queued buffer flush pending */
+#define TTY_HUPPING 21 /* ->hangup() in progress */
#define TTY_WRITE_FLUSH(tty) tty_write_flush((tty))