linux-hardening - [PATCH] CIFS: Fix a potencially linear read overflow

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Date:   Tue, 17 Aug 2021 12:27:09 +0200
From:   Len Baker <len.baker@....com>
To:     Steve French <sfrench@...ba.org>, Jeff Layton <jlayton@...nel.org>,
        Suresh Jayaraman <sjayaraman@...e.de>
Cc:     Len Baker <len.baker@....com>, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-kernel@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH] CIFS: Fix a potencially linear read overflow

strlcpy() reads the entire source buffer first. This read may exceed the
destination size limit. This is both inefficient and can lead to linear
read overflows if a source string is not NUL-terminated.

Also, the strnlen() call does not avoid the read overflow in the strlcpy
function when a not NUL-terminated string is passed.

So, replace this block by a call to kstrndup() that avoids this type of
overflow and does the same.

Fixes: 066ce6899484d ("cifs: rename cifs_strlcpy_to_host and make it use new functions")
Signed-off-by: Len Baker <len.baker@....com>
---
 fs/cifs/cifs_unicode.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/fs/cifs/cifs_unicode.c b/fs/cifs/cifs_unicode.c
index 9bd03a231032..171ad8b42107 100644
--- a/fs/cifs/cifs_unicode.c
+++ b/fs/cifs/cifs_unicode.c
@@ -358,14 +358,9 @@ cifs_strndup_from_utf16(const char *src, const int maxlen,
 		if (!dst)
 			return NULL;
 		cifs_from_utf16(dst, (__le16 *) src, len, maxlen, codepage,
-			       NO_MAP_UNI_RSVD);
+				NO_MAP_UNI_RSVD);
 	} else {
-		len = strnlen(src, maxlen);
-		len++;
-		dst = kmalloc(len, GFP_KERNEL);
-		if (!dst)
-			return NULL;
-		strlcpy(dst, src, len);
+		dst = kstrndup(src, maxlen, GFP_KERNEL);
 	}

 	return dst;
--
2.25.1