From: Ido Schimmel <[email protected]>
Date: Mon, 18 Dec 2017 10:13:20 +0200
> Since commit 0ddcf43d5d4a ("ipv4: FIB Local/MAIN table collapse") the
> local table uses the same trie allocated for the main table when custom
> rules are not in use.
>
> When a net namespace is dismantled, the main table is flushed and freed
> (via an RCU callback) before the local table. In case the callback is
> invoked before the local table is iterated, a use-after-free can occur.
>
> Fix this by iterating over the FIB tables in reverse order, so that the
> main table is always freed after the local table.
>
> Fixes: 0ddcf43d5d4a ("ipv4: FIB Local/MAIN table collapse")
> Signed-off-by: Ido Schimmel <[email protected]>
> Reported-by: Fengguang Wu <[email protected]>
This is really too clever of a fix I think :-)
I would prefer if we fixed things more explicitly.
In struct fib_table you can add a "data_ref" integer. Any pointer
reference created to fib_table->__data increases this counter. It is
always done inside of RTNL locking, so should be doable without
atomics or extra locking.
For a non-aliased fib_table we go:
if (!--fib_table->data_ref)
kfree(fib_table);
And for aliased ones we do something like:
if (fib_table->tb_data != fib_table->__data) {
void *data = fib_table->fb_data;
struct fib_table *alias;
alias = container_of(data, struct fib_table, __data[0]);
if (!--alias->data_ref)
kfree(alias);
kfree(fib_table);
}
Something like that.
