linux-kernel - [PATCH] printk: Fix panic caused by passing log_buf

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Message-ID: <1537285354-430044-1-git-send-email-zhe.he@windriver.com>
Date:   Tue, 18 Sep 2018 23:42:34 +0800
From:   <zhe.he@...driver.com>
To:     <pmladek@...e.com>, <sergey.senozhatsky@...il.com>,
        <rostedt@...dmis.org>, <linux-kernel@...r.kernel.org>
CC:     <zhe.he@...driver.com>
Subject: [PATCH] printk: Fix panic caused by passing log_buf_len to command line

From: He Zhe <zhe.he@...driver.com>

log_buf_len_setup does not check input argument before passing it to
simple_strtoull. The argument would be a NULL pointer if "log_buf_len",
without its value, is set in command line and thus causes the following
panic.

PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1
[    0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70
...
[    0.000000] Call Trace:
[    0.000000]  simple_strtoull+0x29/0x70
[    0.000000]  memparse+0x26/0x90
[    0.000000]  log_buf_len_setup+0x17/0x22
[    0.000000]  do_early_param+0x57/0x8e
[    0.000000]  parse_args+0x208/0x320
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_options+0x29/0x2d
[    0.000000]  ? rdinit_setup+0x30/0x30
[    0.000000]  parse_early_param+0x36/0x4d
[    0.000000]  setup_arch+0x336/0x99e
[    0.000000]  start_kernel+0x6f/0x4ee
[    0.000000]  x86_64_start_reservations+0x24/0x26
[    0.000000]  x86_64_start_kernel+0x6f/0x72
[    0.000000]  secondary_startup_64+0xa4/0xb0

This patch adds a check to prevent the panic, adds KBUILD_MODNAME to
prints and correct bare use of 'unsigned'.

Signed-off-by: He Zhe <zhe.he@...driver.com>
Cc: stable@...r.kernel.org
Cc: pmladek@...e.com
Cc: sergey.senozhatsky@...il.com
Cc: rostedt@...dmis.org
---
 kernel/printk/printk.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9bf5404..f6d4030 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -16,6 +16,8 @@
  *	01Mar01 Andrew Morton
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/tty.h>
@@ -1048,7 +1050,14 @@ static void __init log_buf_len_update(unsigned size)
 /* save requested log_buf_len since it's too early to process it */
 static int __init log_buf_len_setup(char *str)
 {
-	unsigned size = memparse(str, &str);
+	unsigned int size;
+
+	if (!str) {
+		pr_err("Config string not provided\n");
+		return -EINVAL;
+	}
+
+	size = memparse(str, &str);
 
 	log_buf_len_update(size);
 
-- 
2.7.4