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authorAlexandre SIMON <Alexandre.Simon@univ-lorraine.fr>2013-02-01 15:31:54 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-02-21 10:04:57 -0800
commitce0030c00f95cf9110d9cdcd41e901e1fb814417 (patch)
tree40b124b99205bd469ed156b682d7f0f4e5726e5a
parent9ad3bfb9e26197c378d6c239180ed7bcf7c29fd8 (diff)
printk: fix buffer overflow when calling log_prefix function from call_console_drivers
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>
-rw-r--r--include/linux/syslog.h6
-rw-r--r--kernel/printk.c13
2 files changed, 18 insertions, 1 deletions
diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index 38911391a139..ce4c66556059 100644
--- 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 */
diff --git a/kernel/printk.c b/kernel/printk.c
index b663c2c95d39..e95c66223d33 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -638,8 +638,19 @@ static void call_console_drivers(unsigned start, unsigned end)
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) {