smb: client: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

In cifssmb.c:
Using strncpy with a length argument equal to strlen(src) is generally
dangerous because it can cause string buffers to not be NUL-terminated.
In this case, however, there was extra effort made to ensure the buffer
was NUL-terminated via a manual NUL-byte assignment. In an effort to rid
the kernel of strncpy() use, let's swap over to using strscpy() which
guarantees NUL-termination on the destination buffer.

To handle the case where ea_name is NULL, let's use the ?: operator to
substitute in an empty string, thereby allowing strscpy to still
NUL-terminate the destintation string.

Interesting note: this flex array buffer may go on to also have some
value encoded after the NUL-termination:
|	if (ea_value_len)
|		memcpy(parm_data->list.name + name_len + 1,
|			ea_value, ea_value_len);

Now for smb2ops.c and smb2transport.c:
Both of these cases are simple, strncpy() is used to copy string
literals which have a length less than the destination buffer's size. We
can simply swap in the new 2-argument version of strscpy() introduced in
Commit e6584c3964f2f ("string: Allow 2-argument strscpy()").

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index 5aee555515730d78031734da95526ee729416216..23b5709ddc311c7366e33505528711363d151a14 100644 (file)
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -5854,10 +5854,8 @@ SetEARetry:
        parm_data->list.EA_flags = 0;
        /* we checked above that name len is less than 255 */
        parm_data->list.name_len = (__u8)name_len;
-       /* EA names are always ASCII */
-       if (ea_name)
-               strncpy(parm_data->list.name, ea_name, name_len);
-       parm_data->list.name[name_len] = '\0';
+       /* EA names are always ASCII and NUL-terminated */
+       strscpy(parm_data->list.name, ea_name ?: "", name_len + 1);
        parm_data->list.value_len = cpu_to_le16(ea_value_len);
        /* caller ensures that ea_value_len is less than 64K but
        we need to ensure that it fits within the smb */

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 2ed456948f34ca0cd88dbe626429694456a681e2..35bf7eb315cdfc1ce92643d7950f8a8dc50a261b 100644 (file)
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3913,7 +3913,7 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
                strcat(message, "W");
        }
        if (!new_oplock)
-               strncpy(message, "None", sizeof(message));
+               strscpy(message, "None");
 
        cinode->oplock = new_oplock;
        cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,

diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 5a3ca62d2f07f72584392975221cbc9b12276fe8..1d6e54f7879e6a5e8034a90d30471fecc02d2d1b 100644 (file)
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -659,7 +659,7 @@ smb2_sign_rqst(struct smb_rqst *rqst, struct TCP_Server_Info *server)
        }
        spin_unlock(&server->srv_lock);
        if (!is_binding && !server->session_estab) {
-               strncpy(shdr->Signature, "BSRSPYL", 8);
+               strscpy(shdr->Signature, "BSRSPYL");
                return 0;
        }