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From: John Ogness <john.ogness@linutronix.de>
Date: Sun, 17 Feb 2019 03:11:20 +0100
Subject: [PATCH] printk: only allow kernel to emergency message
Emergency messages exist as a mechanism for the kernel to
communicate critical information to users. It is not meant for
use by userspace. Only allow facility=0 messages to be
processed by the emergency message code.
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/printk/printk.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1754,7 +1754,8 @@ static void printk_write_history(struct
* The console_lock must be held.
*/
static void call_console_drivers(u64 seq, const char *ext_text, size_t ext_len,
- const char *text, size_t len, int level)
+ const char *text, size_t len, int level,
+ int facility)
{
struct console *con;
@@ -1774,13 +1775,14 @@ static void call_console_drivers(u64 seq
con->wrote_history = 1;
con->printk_seq = seq - 1;
}
- if (con->write_atomic && level < emergency_console_loglevel) {
+ if (con->write_atomic && level < emergency_console_loglevel &&
+ facility == 0) {
/* skip emergency messages, already printed */
if (con->printk_seq < seq)
con->printk_seq = seq;
continue;
}
- if (con->flags & CON_BOOT) {
+ if (con->flags & CON_BOOT && facility == 0) {
/* skip emergency messages, already printed */
if (con->printk_seq < seq)
con->printk_seq = seq;
@@ -1951,7 +1953,10 @@ asmlinkage int vprintk_emit(int facility
* - text points to beginning of text
* - there is room before text for prefix
*/
- printk_emergency(rbuf, level & 7, ts_nsec, cpu, text, text_len);
+ if (facility == 0) {
+ /* only the kernel can create emergency messages */
+ printk_emergency(rbuf, level & 7, ts_nsec, cpu, text, text_len);
+ }
if ((lflags & LOG_CONT) || !(lflags & LOG_NEWLINE)) {
cont_add(ctx, cpu, caller_id, facility, level, lflags, text, text_len);
@@ -2715,8 +2720,8 @@ static int printk_kthread_func(void *dat
&len, printk_time);
console_lock();
- call_console_drivers(master_seq, ext_text,
- ext_len, text, len, msg->level);
+ call_console_drivers(master_seq, ext_text, ext_len, text, len,
+ msg->level, msg->facility);
if (len > 0 || ext_len > 0)
printk_delay(msg->level);
console_unlock();
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