linux-kernel - [PATCH 01/15] Char: lp, protect LPGETSTATUS with port

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Date:	Tue,  7 May 2013 16:18:09 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	jirislaby@...il.com
Cc:	linux-kernel@...r.kernel.org,
	"salina@...ibm.com" <salina@...ibm.com>, okir@...e.de,
	Jiri Slaby <jslaby@...e.cz>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH 01/15] Char: lp, protect LPGETSTATUS with port_mutex

From: "salina@...ibm.com" <salina@...ibm.com>

The patch fixes a problem in the lp driver that can cause oopses as
follows:
process A:	calls lp_write, which in turn calls
		parport_ieee1284_write_compat, and that invokes
		parport_wait_peripheral
process B:	meanwhile does an ioctl(LPGETSTATUS), which call
		lp_release_parport when done. This function will set
		physport->cad = NULL.
process A:	parport_wait_peripheral tries to dereference
		physport->cad and dies

So, protect that code with the port_mutex in order to protect against
simultaneous calls to lp_read/lp_write.

Similar protection is probably required for ioctl(LPRESET)...

This patch was done by IBM a while back and we (at suse) have that
since at least 2004 in our repos. Let's make it upstream.

Signed-off-by: okir@...e.de
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/char/lp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/char/lp.c b/drivers/char/lp.c
index dafd9ac..0913d79 100644
--- a/drivers/char/lp.c
+++ b/drivers/char/lp.c
@@ -622,9 +622,12 @@ static int lp_do_ioctl(unsigned int minor, unsigned int cmd,
 				return -EFAULT;
 			break;
 		case LPGETSTATUS:
+			if (mutex_lock_interruptible(&lp_table[minor].port_mutex))
+				return -EINTR;
 			lp_claim_parport_or_block (&lp_table[minor]);
 			status = r_str(minor);
 			lp_release_parport (&lp_table[minor]);
+			mutex_unlock(&lp_table[minor].port_mutex);
 
 			if (copy_to_user(argp, &status, sizeof(int)))
 				return -EFAULT;
-- 
1.8.2.1

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