linux-kernel - do_tty_write() can block even with O

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Wed, 2 May 2007 11:17:00 -0400
From:	Dave Johnson <djohnson+linux-kernel@...starentnetworks.com>
To:	linux-kernel@...r.kernel.org
Subject: do_tty_write() can block even with O_NONBLOCK?

I have two processes with the same tty open, one opens blocking and
one opens nonblocking.

If the blocking process blocks doing a write (due to flow control,
just going to fast, etc...) the nonblocking process will also block
when it writes until the blocking process unblocks.

This seems to occur because do_tty_write() isn't checking for
O_NONBLOCK when taking the tty's write mutex.

Signed-off-by: Dave Johnson <djohnson+linux-kernel@...starentnetworks.com>

===== drivers/char/tty_io.c 1.237 vs edited =====
--- 1.237/drivers/char/tty_io.c	2007-03-18 16:40:06 -04:00
+++ edited/drivers/char/tty_io.c	2007-05-01 10:53:27 -04:00
@@ -1690,9 +1690,13 @@
 	ssize_t ret = 0, written = 0;
 	unsigned int chunk;

-	/* FIXME: O_NDELAY ... */
-	if (mutex_lock_interruptible(&tty->atomic_write_lock)) {
-		return -ERESTARTSYS;
+	if (file->f_flags & O_NONBLOCK) {
+		if (!mutex_trylock(&tty->atomic_write_lock))
+			return -EAGAIN;
+	}
+	else {
+		if (mutex_lock_interruptible(&tty->atomic_write_lock))
+			return -ERESTARTSYS;
 	}

 	/*

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/