CVE-2023-54243

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ebtables: fix table blob use-after-free

We are not allowed to return an error at this point. Looking at the code it looks like ret is always 0 at this point, but its not.

t = find_table_lock(net, repl->name, &ret, &ebt_mutex);

... this can return a valid table, with ret != 0.

This bug causes update of table->private with the new blob, but then frees the blob right away in the caller.

Syzbot report:

BUG: KASAN: vmalloc-out-of-bounds in __ebt_unregister_table+0xc00/0xcd0 net/bridge/netfilter/ebtables.c:1168 Read of size 4 at addr ffffc90005425000 by task kworker/u4:4/74 Workqueue: netns cleanup_net Call Trace: kasan_report+0xbf/0x1f0 mm/kasan/report.c:517 __ebt_unregister_table+0xc00/0xcd0 net/bridge/netfilter/ebtables.c:1168 ebt_unregister_table+0x35/0x40 net/bridge/netfilter/ebtables.c:1372 ops_exit_list+0xb0/0x170 net/core/net_namespace.c:169 cleanup_net+0x4ee/0xb10 net/core/net_namespace.c:613 ...

ip(6)tables appears to be ok (ret should be 0 at this point) but make this more obvious.

A use-after-free vulnerability exists in the Linux kernel netfilter ebtables path where a table’s private blob may be replaced but then freed on an unexpected error return, leaving a dangling pointer. A local attacker with low privileges (typically requiring CAP_NET_ADMIN in a network namespace) could trigger it by performing table replacement in a way that hits the inconsistent find_table_lock() return state and then causing table teardown (e.g., via netns cleanup), leading to kernel memory corruption and a crash.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.