From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
stable@vger.kernel.org,
Alexandre SIMON <Alexandre.Simon@univ-lorraine.fr>
Subject: [ 1/1] printk: fix buffer overflow when calling log_prefix function from call_console_drivers
Date: Mon, 18 Feb 2013 10:24:56 -0800 [thread overview]
Message-ID: <20130218181454.976143076@linuxfoundation.org> (raw)
In-Reply-To: <20130218181454.615592566@linuxfoundation.org>
3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Alexandre SIMON <Alexandre.Simon@univ-lorraine.fr>
This patch corrects a buffer overflow in kernels from 3.0 to 3.4 when calling
log_prefix() function from call_console_drivers().
This bug existed in previous releases but has been revealed with commit
162a7e7500f9664636e649ba59defe541b7c2c60 (2.6.39 => 3.0) that made changes
about how to allocate memory for early printk buffer (use of memblock_alloc).
It disappears with commit 7ff9554bb578ba02166071d2d487b7fc7d860d62 (3.4 => 3.5)
that does a refactoring of printk buffer management.
In log_prefix(), the access to "p[0]", "p[1]", "p[2]" or
"simple_strtoul(&p[1], &endp, 10)" may cause a buffer overflow as this
function is called from call_console_drivers by passing "&LOG_BUF(cur_index)"
where the index must be masked to do not exceed the buffer's boundary.
The trick is to prepare in call_console_drivers() a buffer with the necessary
data (PRI field of syslog message) to be safely evaluated in log_prefix().
This patch can be applied to stable kernel branches 3.0.y, 3.2.y and 3.4.y.
Without this patch, one can freeze a server running this loop from shell :
$ export DUMMY=`cat /dev/urandom | tr -dc '12345AZERTYUIOPQSDFGHJKLMWXCVBNazertyuiopqsdfghjklmwxcvbn' | head -c255`
$ while true do ; echo $DUMMY > /dev/kmsg ; done
The "server freeze" depends on where memblock_alloc does allocate printk buffer :
if the buffer overflow is inside another kernel allocation the problem may not
be revealed, else the server may hangs up.
Signed-off-by: Alexandre SIMON <Alexandre.Simon@univ-lorraine.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/syslog.h | 6 ++++++
kernel/printk.c | 13 ++++++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -47,6 +47,12 @@
#define SYSLOG_FROM_CALL 0
#define SYSLOG_FROM_FILE 1
+/*
+ * Syslog priority (PRI) maximum length in char : '<[0-9]{1,3}>'
+ * See RFC5424 for details
+*/
+#define SYSLOG_PRI_MAX_LENGTH 5
+
int do_syslog(int type, char __user *buf, int count, bool from_file);
#endif /* _LINUX_SYSLOG_H */
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -638,8 +638,19 @@ static void call_console_drivers(unsigne
start_print = start;
while (cur_index != end) {
if (msg_level < 0 && ((end - cur_index) > 2)) {
+ /*
+ * prepare buf_prefix, as a contiguous array,
+ * to be processed by log_prefix function
+ */
+ char buf_prefix[SYSLOG_PRI_MAX_LENGTH+1];
+ unsigned i;
+ for (i = 0; i < ((end - cur_index)) && (i < SYSLOG_PRI_MAX_LENGTH); i++) {
+ buf_prefix[i] = LOG_BUF(cur_index + i);
+ }
+ buf_prefix[i] = '\0'; /* force '\0' as last string character */
+
/* strip log prefix */
- cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
+ cur_index += log_prefix((const char *)&buf_prefix, &msg_level, NULL);
start_print = cur_index;
}
while (cur_index != end) {
next prev parent reply other threads:[~2013-02-18 18:25 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-18 18:24 [ 0/1] 3.4.33-stable review Greg Kroah-Hartman
2013-02-18 18:24 ` Greg Kroah-Hartman [this message]
2013-02-20 13:02 ` [ 1/1] printk: fix buffer overflow when calling log_prefix function from call_console_drivers Satoru Takeuchi
2013-02-20 13:43 ` Alexandre SIMON
2013-02-20 15:56 ` Satoru Takeuchi
2013-02-19 2:50 ` [ 0/1] 3.4.33-stable review Shuah Khan
2013-02-20 2:51 ` Greg Kroah-Hartman
2013-02-20 3:31 ` Shuah Khan
2013-02-20 13:09 ` Satoru Takeuchi
2013-02-18 18:25 [ 0/1] 3.0.66-stable review Greg Kroah-Hartman
2013-02-18 18:25 ` [ 1/1] printk: fix buffer overflow when calling log_prefix function from call_console_drivers Greg Kroah-Hartman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20130218181454.976143076@linuxfoundation.org \
--to=gregkh@linuxfoundation.org \
--cc=Alexandre.Simon@univ-lorraine.fr \
--cc=linux-kernel@vger.kernel.org \
--cc=stable@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).