Messages in this thread Patch in this message | | | Subject | [PATCH] tty reference count fix | From | Paul Fulghum <> | Date | Mon, 13 Feb 2006 14:13:30 -0600 |
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Fix hole where tty structure can be released when reference count is non zero. Existing code can sleep without tty_sem protection between deciding to release the tty structure (setting local variables tty_closing and otty_closing) and setting TTY_CLOSING to prevent further opens. An open can occur during this interval causing release_dev() to free the tty structure while it is still referenced.
This should fix bugzilla.kernel.org [Bug 6041] New: Unable to handle kernel paging request
In Bug 6041, tty_open() oopes on accessing the tty structure it has successfully claimed. Bug was on SMP machine with the same tty being opened and closed by multiple processes, and DEBUG_PAGEALLOC enabled.
Signed-off-by: Paul Fulghum <paulkf@microgate.com> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Jesper Juhl <jesper.juhl@gmail.com>
--- linux/drivers/char/tty_io.c 2006-02-10 15:54:00.000000000 -0600 +++ b/drivers/char/tty_io.c 2006-02-13 13:14:33.000000000 -0600 @@ -1841,7 +1841,6 @@ static void release_dev(struct file * fi tty_closing = tty->count <= 1; o_tty_closing = o_tty && (o_tty->count <= (pty_master ? 1 : 0)); - up(&tty_sem); do_sleep = 0; if (tty_closing) { @@ -1869,6 +1868,7 @@ static void release_dev(struct file * fi printk(KERN_WARNING "release_dev: %s: read/write wait queue " "active!\n", tty_name(tty, buf)); + up(&tty_sem); schedule(); } @@ -1877,8 +1877,6 @@ static void release_dev(struct file * fi * both sides, and we've completed the last operation that could * block, so it's safe to proceed with closing. */ - - down(&tty_sem); if (pty_master) { if (--o_tty->count < 0) { printk(KERN_WARNING "release_dev: bad pty slave count " @@ -1892,7 +1890,6 @@ static void release_dev(struct file * fi tty->count, tty_name(tty, buf)); tty->count = 0; } - up(&tty_sem); /* * We've decremented tty->count, so we need to remove this file @@ -1937,6 +1934,8 @@ static void release_dev(struct file * fi read_unlock(&tasklist_lock); } + up(&tty_sem); + /* check whether both sides are closing ... */ if (!tty_closing || (o_tty && !o_tty_closing)) return;
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