[PATCH 5.9 208/255] bootconfig: Extend the magic check range to the preceding 3 bytes

Greg Kroah-Hartman
2020-11-17T13:45:10Z

From: Masami Hiramatsu <mhiramat@kernel.org>

commit 50b8a742850fce7293bed45753152c425f7e931b upstream.

Since Grub may align the size of initrd to 4 if user pass
initrd from cpio, we have to check the preceding 3 bytes as well.

Link: https://lkml.kernel.org/r/160520205132.303174.4876760192433315429.stgit@devnote2

Cc: stable@vger.kernel.org
Fixes: 85c46b78da58 ("bootconfig: Add bootconfig magic word for indicating bootconfig explicitly")
Reported-by: Chen Yu <yu.chen.surf@gmail.com>
Tested-by: Chen Yu <yu.chen.surf@gmail.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
init/main.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)

--- a/init/main.c
+++ b/init/main.c
@@ -267,14 +267,24 @@ static void * __init get_boot_config_fro
u32 size, csum;
char *data;
u32 *hdr;
+ int i;

if (!initrd_end)
return NULL;

data = (char *)initrd_end - BOOTCONFIG_MAGIC_LEN;
- if (memcmp(data, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN))
- return NULL;
+ /*
+ * Since Grub may align the size of initrd to 4, we must
+ * check the preceding 3 bytes as well.
+ */
+ for (i = 0; i < 4; i++) {
+ if (!memcmp(data, BOOTCONFIG_MAGIC, BOOTCONFIG_MAGIC_LEN))
+ goto found;
+ data--;
+ }
+ return NULL;

+found:
hdr = (u32 *)(data - 8);
size = hdr[0];
csum = hdr[1];