[PATCH v2 1/2] mm/page_alloc: Fix panic caused by passing debug_guardpage_minorder or kernelcore to command line

[zhe.he]

From: He Zhe <zhe.he@xxxxxxxxxxxxx>

debug_guardpage_minorder_setup and cmdline_parse_kernelcore do not check
input argument before using it. The argument would be a NULL pointer if
"debug_guardpage_minorder" or "kernelcore", without its value, is set in
command line and thus causes the following panic.

PANIC: early exception 0xe3 IP 10:ffffffffa08146f1 error 0 cr2 0x0
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #11
[    0.000000] RIP: 0010:parse_option_str+0x11/0x90
...
[    0.000000] Call Trace:
[    0.000000]  cmdline_parse_kernelcore+0x19/0x41
[    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 adds KBUILD_MODNAME to
prints.

Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: akpm@xxxxxxxxxxxxxxxxxxxx
Cc: mhocko@xxxxxxxx
Cc: vbabka@xxxxxxx
Cc: pasha.tatashin@xxxxxxxxxx
Cc: mgorman@xxxxxxxxxxxxxxxxxxx
Cc: aaron.lu@xxxxxxxxx
Cc: osalvador@xxxxxxx
Cc: iamjoonsoo.kim@xxxxxxx
---
v2:
Use more clear error info
Split the addition of KBUILD_MODNAME out

 mm/page_alloc.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 89d2a2a..f34cae1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -630,6 +630,12 @@ static int __init debug_guardpage_minorder_setup(char *buf)
 {
 	unsigned long res;
 
+	if (!buf) {
+		pr_err("kernel option debug_guardpage_minorder requires an \
+			argument\n");
+		return -EINVAL;
+	}
+
 	if (kstrtoul(buf, 10, &res) < 0 ||  res > MAX_ORDER / 2) {
 		pr_err("Bad debug_guardpage_minorder value\n");
 		return 0;
@@ -6952,6 +6958,11 @@ static int __init cmdline_parse_core(char *p, unsigned long *core,
  */
 static int __init cmdline_parse_kernelcore(char *p)
 {
+	if (!p) {
+		pr_err("kernel option kernelcore requires an argument\n");
+		return -EINVAL;
+	}
+
 	/* parse kernelcore=mirror */
 	if (parse_option_str(p, "mirror")) {
 		mirrored_kernelcore = true;
-- 
2.7.4