linux-kernel - Re: [PATCH] x86,boot: standardize strcmp()

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Date:	Tue, 17 Mar 2015 15:28:00 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Arjun Sreedharan <arjun024@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86,boot: standardize strcmp()

On Tue, Mar 17, 2015 at 08:46:08AM +0100, Ingo Molnar wrote:
> I'd also add the following to the changelog:

Added:

---
From: Arjun Sreedharan <arjun024@...il.com>
Date: Mon, 16 Mar 2015 21:07:47 +0530
Subject: [PATCH] x86/boot: Standardize strcmp()

strcmp() is always expected to return 0 when arguments are equal,
negative when its first argument @str1 is less than its second argument
@str2 and a positive value otherwise. Previously strcmp("a", "b")
returned 1. Now it gives -1, as it is supposed to.

Until now this bug never triggered, because all uses for strcmp() in the
boot code tested for nonzero:

  triton:~/tip> git grep strcmp arch/x86/boot/
  arch/x86/boot/boot.h:int strcmp(const char *str1, const char *str2);
  arch/x86/boot/edd.c:            if (!strcmp(eddarg, "skipmbr") || !strcmp(eddarg, "skip")) {
  arch/x86/boot/edd.c:            else if (!strcmp(eddarg, "off"))
  arch/x86/boot/edd.c:            else if (!strcmp(eddarg, "on"))

should in the future strcmp() be used in a comparative way in the boot
code, it might have led to (not so subtle) bugs.

Signed-off-by: Arjun Sreedharan <arjun024@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
Link: http://lkml.kernel.org/r/1426520267-1803-1-git-send-email-arjun024@gmail.com
Signed-off-by: Borislav Petkov <bp@...e.de>
---
 arch/x86/boot/string.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index 493f3fd9f139..318b8465d302 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -30,7 +30,7 @@ int strcmp(const char *str1, const char *str2)
 	int delta = 0;
 
 	while (*s1 || *s2) {
-		delta = *s2 - *s1;
+		delta = *s1 - *s2;
 		if (delta)
 			return delta;
 		s1++;
-- 
2.3.3

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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