[PATCH v3 1/2] printk: Fix panic caused by passing log_buf_len to command line

[zhe.he]

From: He Zhe <zhe.he@xxxxxxxxxxxxx>

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 and a check to report if someone is
setting it over 4G.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: pmladek@xxxxxxxx
Cc: sergey.senozhatsky@xxxxxxxxx
Cc: rostedt@xxxxxxxxxxx
---
v2:
Split out the addition of pr_fmt and the unsigned update
v3:
Remove error message for NULL pointer
Add check and error message for over 4G use

 kernel/printk/printk.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9bf5404..1c932b6 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1037,18 +1037,29 @@ void log_buf_vmcoreinfo_setup(void)
 static unsigned long __initdata new_log_buf_len;
 
 /* we practice scaling the ring buffer by powers of 2 */
-static void __init log_buf_len_update(unsigned size)
+static void __init log_buf_len_update(u64 size)
 {
+	if (size > UINT_MAX) {
+		size = UINT_MAX;
+		pr_err("log_buf over 4G is not supported.\n");
+	}
+
 	if (size)
 		size = roundup_pow_of_two(size);
 	if (size > log_buf_len)
-		new_log_buf_len = size;
+		new_log_buf_len = (unsigned long)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);
+	u64 size;
+
+	if (!str) {
+		return -EINVAL;
+	}
+
+	size = memparse(str, &str);
 
 	log_buf_len_update(size);
 
-- 
2.7.4