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From:   Len Baker <len.baker@gmx.com>
To:     Steve French <sfrench@samba.org>, Jeff Layton <jlayton@kernel.org>,
        Suresh Jayaraman <sjayaraman@suse.de>
Cc:     Len Baker <len.baker@gmx.com>, linux-cifs@vger.kernel.org,
        samba-technical@lists.samba.org, linux-kernel@vger.kernel.org,
        Kees Cook <keescook@chromium.org>,
        linux-hardening@vger.kernel.org
Subject: [PATCH] CIFS: Fix a potencially linear read overflow
Date:   Tue, 17 Aug 2021 12:27:09 +0200
Message-Id: <20210817102709.15046-1-len.baker@gmx.com>
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

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 n=
ew functions")
Signed-off-by: Len Baker <len.baker@gmx.com>
=2D--
 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
=2D-- 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 ma=
xlen,
 		if (!dst)
 			return NULL;
 		cifs_from_utf16(dst, (__le16 *) src, len, maxlen, codepage,
-			       NO_MAP_UNI_RSVD);
+				NO_MAP_UNI_RSVD);
 	} else {
-		len =3D strnlen(src, maxlen);
-		len++;
-		dst =3D kmalloc(len, GFP_KERNEL);
-		if (!dst)
-			return NULL;
-		strlcpy(dst, src, len);
+		dst =3D kstrndup(src, maxlen, GFP_KERNEL);
 	}

 	return dst;
=2D-
2.25.1