linux-kernel - [PATCH 4.14 080/217] CIFS: Fix a potencially linear read overflow

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Date:   Mon, 20 Sep 2021 18:41:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Len Baker <len.baker@....com>,
        "Paulo Alcantara (SUSE)" <pc@....nz>,
        Jeff Layton <jlayton@...nel.org>,
        Steve French <stfrench@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.14 080/217] CIFS: Fix a potencially linear read overflow

From: Len Baker <len.baker@....com>

[ Upstream commit f980d055a0f858d73d9467bb0b570721bbfcdfb8 ]

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>
Reviewed-by: Paulo Alcantara (SUSE) <pc@....nz>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 9986817532b1..7932e20555d2 100644
--- a/fs/cifs/cifs_unicode.c
+++ b/fs/cifs/cifs_unicode.c
@@ -371,14 +371,9 @@ 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;
-- 
2.30.2