[PATCH 5.15.y] smb: server: Fix extension string in ksmbd_extract_shortname()

[Sasha Levin <sashal@kernel.org>]

From: Thorsten Blum <thorsten.blum@linux.dev>

[ Upstream commit 8e7d178d06e8937454b6d2f2811fa6a15656a214 ]

In ksmbd_extract_shortname(), strscpy() is incorrectly called with the
length of the source string (excluding the NUL terminator) rather than
the size of the destination buffer. This results in "__" being copied
to 'extension' rather than "___" (two underscores instead of three).

Use the destination buffer size instead to ensure that the string "___"
(three underscores) is copied correctly.

Cc: stable@vger.kernel.org
Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/ksmbd/smb_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ksmbd/smb_common.c b/fs/ksmbd/smb_common.c
index e90a1e8c1951..0438a634f4c2 100644
--- a/fs/ksmbd/smb_common.c
+++ b/fs/ksmbd/smb_common.c
@@ -508,7 +508,7 @@ int ksmbd_extract_shortname(struct ksmbd_conn *conn, const char *longname,
 
 	p = strrchr(longname, '.');
 	if (p == longname) { /*name starts with a dot*/
-		strscpy(extension, "___", strlen("___"));
+		strscpy(extension, "___", sizeof(extension));
 	} else {
 		if (p) {
 			p++;
-- 
2.39.5