[PATCH 5.10 190/236] CIFS: Fix a potencially linear read overflow

Greg Kroah-Hartman
2021-09-13T13:47:41Z

From: Len Baker <len.baker@gmx.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@gmx.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.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 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;
--
2.30.2