linux-kernel - [PATCH] drivers/base: Fix length checks in create_syslog_header()/dev_vprintk

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Message-ID: <1388164698.26981.73.camel@deadeye.wl.decadent.org.uk>
Date:	Fri, 27 Dec 2013 18:18:18 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Joe Perches <joe@...ches.com>,
	Kay Sievers <kay@...y.org>
Subject: [PATCH] drivers/base: Fix length checks in
 create_syslog_header()/dev_vprintk_emit()

snprintf() returns the number of bytes that could have been written
(excluding the null), not the actual number of bytes written.  Given a
long enough subsystem or device name, these functions will advance
beyond the end of the on-stack buffer in dev_vprintk_exit(), resulting
in an information leak or stack corruption.  I don't know whether such
a long name is currently possible.

In case snprintf() returns a value >= the buffer size, do not add
structured logging information.  Also WARN the first time this
happens, so we can fix the driver or increase the buffer size.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/base/core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67b180d..989a93c 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2022,6 +2022,8 @@ create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
 		return 0;
 
 	pos += snprintf(hdr + pos, hdrlen - pos, "SUBSYSTEM=%s", subsys);
+	if (pos >= hdrlen)
+		goto overflow;
 
 	/*
 	 * Add device identifier DEVICE=:
@@ -2053,7 +2055,14 @@ create_syslog_header(const struct device *dev, char *hdr, size_t hdrlen)
 				"DEVICE=+%s:%s", subsys, dev_name(dev));
 	}
 
+	if (pos >= hdrlen)
+		goto overflow;
+
 	return pos;
+
+overflow:
+	dev_WARN_ONCE(dev, 1, "device/subsystem name too long");
+	return 0;
 }
 EXPORT_SYMBOL(create_syslog_header);
 

-- 
Ben Hutchings
Computers are not intelligent.	They only think they are.

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