CVE-2024-42109

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

netfilter: nf_tables: unconditionally flush pending work before notifier

syzbot reports:

KASAN: slab-uaf in nft_ctx_update include/net/netfilter/nf_tables.h:1831

KASAN: slab-uaf in nft_commit_release net/netfilter/nf_tables_api.c:9530

KASAN: slab-uaf int nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597

Read of size 2 at addr ffff88802b0051c4 by task kworker/1:1/45

[..]

Workqueue: events nf_tables_trans_destroy_work

Call Trace:

nft_ctx_update include/net/netfilter/nf_tables.h:1831 [inline]

nft_commit_release net/netfilter/nf_tables_api.c:9530 [inline]

nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597

Problem is that the notifier does a conditional flush, but its possible

that the table-to-be-removed is still referenced by transactions being

processed by the worker, so we need to flush unconditionally.

We could make the flush_work depend on whether we found a table to delete

in nf-next to avoid the flush for most cases.

AFAICS this problem is only exposed in nf-next, with

commit e169285f8c56 ("netfilter: nf_tables: do not store nft_ctx in transaction objects"),

with this commit applied there is an unconditional fetch of

table->family which is whats triggering the above splat.