network: fix a potential divide-by-zero (#37705)

In function `tc_init`, hz is parsed from the content of file
`"/proc/net/psched"` and can be 0.
In function `hierarchy_token_bucket_class_verify`, hz is directly used
as a divisor in
`htb->buffer = htb->rate / hz + htb->mtu;` without any check. This adds a check on hz before using it as a divisor.

Co-authored-by: jinyaoguo <[email protected]>
(cherry picked from commit 1a596054a0f937bfc244580f07510759a0e45657)
(cherry picked from commit e2c9fdd5c0f84eb234e122fe8fce9c4d949882cd)
(cherry picked from commit 64206ad1372a7df4c96c1fd8cd363a6032eaeadf)

Author: 2 people

src/network/tc/htb.c

@@ -470,6 +470,8 @@ static int hierarchy_token_bucket_class_verify(TClass *tclass) {
         if (r < 0)
                 return log_error_errno(r, "Failed to read /proc/net/psched: %m");
 
+        /* Kernel would never hand us 0 Hz. */
+        assert(hz > 0);
         if (htb->buffer == 0)
                 htb->buffer = htb->rate / hz + htb->mtu;
         if (htb->ceil_buffer == 0)