netdev - [PATCH net-next 1/3] pktgen: fix out-of-bounds access in pgctrl

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Date:	Fri, 21 Feb 2014 21:38:34 +0100
From:	Mathias Krause <minipli@...glemail.com>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, Mathias Krause <minipli@...glemail.com>
Subject: [PATCH net-next 1/3] pktgen: fix out-of-bounds access in pgctrl_write()

If a privileged user writes an empty string to /proc/net/pktgen/pgctrl
the code for stripping the (then non-existent) '\n' actually writes the
zero byte at index -1 of data[]. The then still uninitialized array will
very likely fail the command matching tests and the pr_warning() at the
end will therefore leak stack bytes to the kernel log.

Fix those issues by simply ensuring we're passed a non-empty string as
the user API apparently expects a trailing '\n' for all commands.

Cc: "David S. Miller" <davem@...emloft.net>
Signed-off-by: Mathias Krause <minipli@...glemail.com>
---
 net/core/pktgen.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index fdac61cac1..cc07c43494 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -485,6 +485,9 @@ static ssize_t pgctrl_write(struct file *file, const char __user *buf,
 		goto out;
 	}

+	if (count == 0)
+		return -EINVAL;
+
 	if (count > sizeof(data))
 		count = sizeof(data);

@@ -492,7 +495,7 @@ static ssize_t pgctrl_write(struct file *file, const char __user *buf,
 		err = -EFAULT;
 		goto out;
 	}
-	data[count - 1] = 0;	/* Make string */
+	data[count - 1] = 0;	/* Strip trailing '\n' and terminate string */

 	if (!strcmp(data, "stop"))
 		pktgen_stop_all_threads_ifs(pn);
-- 
1.7.10.4

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