[PATCH V4] init: Handle bootloader identifier in kernel parameters

[Huacai Chen <chenhuacai@loongson.cn>]

BootLoader (Grub, LILO, etc) may pass an identifier such as "BOOT_IMAGE=
/boot/vmlinuz-x.y.z" to kernel parameters. But these identifiers are not
recognized by the kernel itself so will be passed to user space. However
user space init program also doesn't recognized it.

KEXEC/KDUMP (kexec-tools) may also pass an identifier such as "kexec" on
some architectures.

We cannot change BootLoader's behavior, because this behavior exists for
many years, and there are already user space programs search BOOT_IMAGE=
in /proc/cmdline to obtain the kernel image locations:

https://github.com/linuxdeepin/deepin-ab-recovery/blob/master/util.go
(search getBootOptions)
https://github.com/linuxdeepin/deepin-ab-recovery/blob/master/main.go
(search getKernelReleaseWithBootOption)

So the the best way is handle (ignore) it by the kernel itself, which
can avoid such boot warnings (if we use something like init=/bin/bash,
bootloader identifier can even cause a crash):

Kernel command line: BOOT_IMAGE=(hd0,1)/vmlinuz-6.x root=/dev/sda3 ro console=tty
Unknown kernel command line parameters "BOOT_IMAGE=(hd0,1)/vmlinuz-6.x", will be passed to user space.

Cc: stable@vger.kernel.org
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
V2: Update comments and commit messages.
V3: Document bootloader identifiers.
V4: Use strstarts() instead of strncmp().

 init/main.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/init/main.c b/init/main.c
index 0ee0ee7b7c2c..9b5150166bcf 100644
--- a/init/main.c
+++ b/init/main.c
@@ -544,6 +544,12 @@ static int __init unknown_bootoption(char *param, char *val,
 				     const char *unused, void *arg)
 {
 	size_t len = strlen(param);
+	/*
+	 * Well-known bootloader identifiers:
+	 * 1. LILO/Grub pass "BOOT_IMAGE=...";
+	 * 2. kexec/kdump (kexec-tools) pass "kexec".
+	 */
+	const char *bootloader[] = { "BOOT_IMAGE=", "kexec", NULL };
 
 	/* Handle params aliased to sysctls */
 	if (sysctl_is_alias(param))
@@ -551,6 +557,12 @@ static int __init unknown_bootoption(char *param, char *val,
 
 	repair_env_string(param, val);
 
+	/* Handle bootloader identifier */
+	for (int i = 0; bootloader[i]; i++) {
+		if (strstarts(param, bootloader[i]))
+			return 0;
+	}
+
 	/* Handle obsolete-style parameters */
 	if (obsolete_checksetup(param))
 		return 0;
-- 
2.47.3