[PATCH 2/5] x86: fix early command-line parsing, when partial word match

Dave Hansen
2015-12-22T22:53:36Z

From: Dave Hansen <dave.hansen@linux.intel.com>

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>
Cc: Borislav Petkov <bp@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org
Cc: fenghua.yu@intel.com
Cc: yu-cheng.yu@intel.com
---

b/arch/x86/lib/cmdline.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff -puN arch/x86/lib/cmdline.c~x86-mid-option-match-command-line-parsing arch/x86/lib/cmdline.c
--- a/arch/x86/lib/cmdline.c~x86-mid-option-match-command-line-parsing 2015-12-22 11:56:59.047167827 -0800
+++ b/arch/x86/lib/cmdline.c 2015-12-22 11:56:59.050167962 -0800
@@ -72,18 +72,26 @@ int cmdline_find_option_bool(const char
*/
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)
_