init: handle bootloader identifier in kernel parameters

BootLoaders (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 userspace.  However
user space init program also don't recognize 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.

[[email protected]: use strstarts()]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Huacai Chen <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Jan Kara <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: chenhuacai

init/main.c

@@ -544,13 +544,25 @@ 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))
 		return 0;
 
 	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;