linux-hardening - [PATCH v5 1/3] Fix unefficient call to memset before memcpu in nla

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20201113111133.15011-2-laniel_francis@privacyrequired.com>
Date:   Fri, 13 Nov 2020 12:11:31 +0100
From:   laniel_francis@...vacyrequired.com
To:     linux-hardening@...r.kernel.org, netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, keescook@...omium.org,
        Francis Laniel <laniel_francis@...vacyrequired.com>
Subject: [PATCH v5 1/3] Fix unefficient call to memset before memcpu in nla_strlcpy.

From: Francis Laniel <laniel_francis@...vacyrequired.com>

Before this commit, nla_strlcpy first memseted dst to 0 then wrote src into it.
This is inefficient because bytes whom number is less than src length are written
twice.

This patch solves this issue by first writing src into dst then fill dst with
0's.
Note that, in the case where src length is higher than dst, only 0 is written.
Otherwise there are as many 0's written to fill dst.

For example, if src is "foo\0" and dst is 5 bytes long, the result will be:
1. "fooGG" after memcpy (G means garbage).
2. "foo\0\0" after memset.

Signed-off-by: Francis Laniel <laniel_francis@...vacyrequired.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
---
 lib/nlattr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/nlattr.c b/lib/nlattr.c
index 74019c8ebf6b..07156e581997 100644
--- a/lib/nlattr.c
+++ b/lib/nlattr.c
@@ -731,8 +731,9 @@ size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize)
 	if (dstsize > 0) {
 		size_t len = (srclen >= dstsize) ? dstsize - 1 : srclen;

-		memset(dst, 0, dstsize);
 		memcpy(dst, src, len);
+		/* Zero pad end of dst. */
+		memset(dst + len, 0, dstsize - len);
 	}

 	return srclen;
-- 
2.20.1