2010-11-14 17:06:17

by Vasily Kulikov

Subject: [PATCH] net: ipv4: tcp_probe: cleanup snprintf() use

snprintf() returns number of bytes that were copied if there is no overflow.
This code uses return value as number of copied bytes. Theoretically format
string '%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n' may be expanded
up to 163 bytes. In reality tv.tv_sec is just few bytes instead of 20, 2 ports
are just 5 bytes each instead of 10, length is 5 bytes instead of 10. The rest
is an unstrusted input. Theoretically if tv_sec is big then copy_to_user() would
overflow tbuf.

tbuf was increased to fit in 163 bytes. snprintf() is used to follow return
value semantic.

Signed-off-by: Vasiliy Kulikov <[email protected]>
---
Compile tested.

Format length:
20 for '%lu'
1 for '.'
9 for '%09lu'
1 for ' '
15 for '%pI4'
1 for ':'
10 for '%u'
1 for ' '
15 for '%pI4'
1 for ':'
10 for '%u'
1 for ' '
11 for '%d'
1 for ' '
10 for '%#x'
1 for ' '
10 for '%#x'
1 for ' '
10 for '%u'
1 for ' '
10 for '%u'
1 for ' '
10 for '%u'
1 for ' '
10 for '%u'
1 for '\n'
163 for '%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n'

net/ipv4/tcp_probe.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_probe.c b/net/ipv4/tcp_probe.c
index 6211e21..3b7bf19 100644
--- a/net/ipv4/tcp_probe.c
+++ b/net/ipv4/tcp_probe.c
@@ -154,7 +154,7 @@ static int tcpprobe_sprint(char *tbuf, int n)
struct timespec tv
= ktime_to_timespec(ktime_sub(p->tstamp, tcp_probe.start));

- return snprintf(tbuf, n,
+ return scnprintf(tbuf, n,
"%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n",
(unsigned long) tv.tv_sec,
(unsigned long) tv.tv_nsec,
@@ -174,7 +174,7 @@ static ssize_t tcpprobe_read(struct file *file, char __user *buf,
return -EINVAL;

while (cnt < len) {
- char tbuf[128];
+ char tbuf[164];
int width;

/* Wait for data in buffer */
--
1.7.0.4

2010-11-17 20:29:57

by David Miller

Subject: Re: [PATCH] net: ipv4: tcp_probe: cleanup snprintf() use

From: Vasiliy Kulikov <[email protected]>
Date: Sun, 14 Nov 2010 20:06:08 +0300

> snprintf() returns number of bytes that were copied if there is no overflow.
> This code uses return value as number of copied bytes. Theoretically format
> string '%lu.%09lu %pI4:%u %pI4:%u %d %#x %#x %u %u %u %u\n' may be expanded
> up to 163 bytes. In reality tv.tv_sec is just few bytes instead of 20, 2 ports
> are just 5 bytes each instead of 10, length is 5 bytes instead of 10. The rest
> is an unstrusted input. Theoretically if tv_sec is big then copy_to_user() would
> overflow tbuf.
>
> tbuf was increased to fit in 163 bytes. snprintf() is used to follow return
> value semantic.
>
> Signed-off-by: Vasiliy Kulikov <[email protected]>

Applied, thanks.