3.0.66-stable review

This is the start of the stable review cycle for the 3.0.66 release. There is 1 patch in this series, which will be posted as a response to this one. If anyone has any issues with it being applied, please let me know.

Responses should be made by Wed Feb 20 18:22:38 UTC 2013. Anything received after that time might be too late.

The whole patch series can be found in one patch at:

	kernel.org/pub/linux/kernel/v3.0/stable-review/patch-3.0.66-rc1.gz

and the diffstat can be found below.

thanks,

greg k-h

-------------
Pseudo-Shortlog of commits:

Greg Kroah-Hartman <[email protected]>

    Linux 3.0.66-rc1

Alexandre SIMON <[email protected]>
printk: fix buffer overflow when calling log_prefix function from call_console_drivers

-------------

Diffstat:

 Makefile               |  4 ++--
 include/linux/syslog.h |  6 ++++++
 kernel/printk.c        | 13 ++++++++++++-
 3 files changed, 20 insertions(+), 3 deletions(-)

3.0-stable review patch. If anyone has any objections, please let me know.

------------------

From: Alexandre SIMON <[email protected]>

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.

---
 include/linux/syslog.h |    6 ++++++
 kernel/printk.c        |   13 ++++++++++++-
 2 files changed, 18 insertions(+), 1 deletion(-)

@@ -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 */

@@ -633,8 +633,19 @@ 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) {

Patches applied cleanly to 3.0.65, and 3.4.32 Compiled and booted on the following systems:
HP EliteBook 6930p Intel(R) Core(TM)2 Duo CPU T9400 @ 2.53GHz HP ProBook 6475b AMD A10-4600M APU with Radeon(tm) HD Graphics

Reviewed patches

Skipped Cross-compile tests

-- Shuah

At Mon, 18 Feb 2013 19:49:17 -0700,

+1.

This kernel can be built and boot without any problem. Building a kernel with this kernel also works fine.
* Its dmesg also looks correct. *

- Build Machine: debian wheezy x86_64
CPU: Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz x 4
memory: 8GB

- Test machine: debian wheezy x86_64(KVM guest on the Build Machine)
vCPU: x2
memory: 2GB

Thanks,
Satoru