x86/boot: Fix early command-line parsing when partial word matches

cmdline_find_option_bool() keeps track of position in two strings:

 1. the command-line
 2. the option we are searchign for in the command-line

We plow through each character in the command-line one at a time, always
moving forward. We move forward in the option ('opptr') when we match
characters in 'cmdline'. We reset the 'opptr' only when we go in to the
'st_wordstart' state.

But, if we fail to match an option because we see a space
(state=st_wordcmp, *opptr='\0',c=' '), we set state='st_wordskip' and
'break', moving to the next character. But, that move to the next
character is the one *after* the ' '. This means that we will miss a
'st_wordstart' state.

For instance, if we have

  cmdline = "foo fool";

and are searching for "fool", we have:

	  "fool"
  opptr = ----^

           "foo fool"
   c = --------^

We see that 'l' != ' ', set state=st_wordskip, break, and then move 'c', so:

          "foo fool"
  c = ---------^

and are still in state=st_wordskip. We will stay in wordskip until we
have skipped "fool", thus missing the option we were looking for. This
*only* happens when you have a partially- matching word followed by a
matching one.

To fix this, we always fall *into* the 'st_wordskip' state when we set
it.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: yu-cheng.yu@intel.com
Link: http://lkml.kernel.org/r/20151222225239.8E1DCA58@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 13 insertions, 5 deletions

diff --git a/arch/x86/lib/cmdline.c b/arch/x86/lib/cmdline.c
index 49548bed2301..ff8d1beead6c 100644
--- a/arch/x86/lib/cmdline.c
+++ b/arch/x86/lib/cmdline.c
@@ -72,18 +72,26 @@ int cmdline_find_option_bool(const char *cmdline, const char *option)
                                  */
                                 if (!c || myisspace(c))
                                         return wstart;
-                                else
-                                        state = st_wordskip;
+                                /*
+                                 * We hit the end of the option, but _not_
+                                 * the end of a word on the cmdline.  Not
+                                 * a match.
+                                 */
                         } else if (!c) {
                                 /*
                                  * Hit the NULL terminator on the end of
                                  * cmdline.
                                  */
                                 return 0;
-                        } else if (c != *opptr++) {
-                                state = st_wordskip;
+                        } else if (c == *opptr++) {
+                                /*
+                                 * We are currently matching, so continue
+                                 * to the next character on the cmdline.
+                                 */
+                                break;
                         }
-                        break;
+                        state = st_wordskip;
+                        /* fall through */
 
                 case st_wordskip:
                         if (!c)