From: Pablo Neira Ayuso pablo@netfilter.org

commit 520778042ccca019f3ffa136dd0ca565c486cedd upstream.

Since 3e135cd499bf ("netfilter: nft_dynset: dynamic stateful expression instantiation"), it is possible to attach stateful expressions to set elements.

cd5125d8f518 ("netfilter: nf_tables: split set destruction in deactivate and destroy phase") introduces conditional destruction on the object to accomodate transaction semantics.

nft_expr_init() calls expr->ops->init() first, then check for NFT_STATEFUL_EXPR, this stills allows to initialize a non-stateful lookup expressions which points to a set, which might lead to UAF since the set is not properly detached from the set->binding for this case. Anyway, this combination is non-sense from nf_tables perspective.

This patch fixes this problem by checking for NFT_STATEFUL_EXPR before expr->ops->init() is called.

The reporter provides a KASAN splat and a poc reproducer (similar to those autogenerated by syzbot to report use-after-free errors). It is unknown to me if they are using syzbot or if they use similar automated tool to locate the bug that they are reporting.

For the record, this is the KASAN splat.

[ 85.431824] ================================================================== [ 85.432901] BUG: KASAN: use-after-free in nf_tables_bind_set+0x81b/0xa20 [ 85.433825] Write of size 8 at addr ffff8880286f0e98 by task poc/776 [ 85.434756] [ 85.434999] CPU: 1 PID: 776 Comm: poc Tainted: G W 5.18.0+ #2 [ 85.436023] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014

Fixes: 0b2d8a7b638b ("netfilter: nf_tables: add helper functions for expression handling") Reported-and-tested-by: Aaron Adams edg-e@nccgroup.com Signed-off-by: Pablo Neira Ayuso pablo@netfilter.org [Ajay: Regenerated the patch for v4.19.y] Signed-off-by: Ajay Kaher akaher@vmware.com --- net/netfilter/nf_tables_api.c | 16 ++++++++++------ net/netfilter/nft_dynset.c | 3 --- 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c index 9cc8e92..ab68076 100644 --- a/net/netfilter/nf_tables_api.c +++ b/net/netfilter/nf_tables_api.c @@ -2167,27 +2167,31 @@ struct nft_expr *nft_expr_init(const struct nft_ctx *ctx,

err = nf_tables_expr_parse(ctx, nla, &info); if (err < 0) - goto err1; + goto err_expr_parse; + + err = -EOPNOTSUPP; + if (!(info.ops->type->flags & NFT_EXPR_STATEFUL)) + goto err_expr_stateful;

err = -ENOMEM; expr = kzalloc(info.ops->size, GFP_KERNEL); if (expr == NULL) - goto err2; + goto err_expr_stateful;

err = nf_tables_newexpr(ctx, &info, expr); if (err < 0) - goto err3; + goto err_expr_new;

return expr; -err3: +err_expr_new: kfree(expr); -err2: +err_expr_stateful: owner = info.ops->type->owner; if (info.ops->type->release_ops) info.ops->type->release_ops(info.ops);

module_put(owner); -err1: +err_expr_parse: return ERR_PTR(err); }

diff --git a/net/netfilter/nft_dynset.c b/net/netfilter/nft_dynset.c index 4e54404..cc076d5 100644 --- a/net/netfilter/nft_dynset.c +++ b/net/netfilter/nft_dynset.c @@ -193,9 +193,6 @@ static int nft_dynset_init(const struct nft_ctx *ctx, return PTR_ERR(priv->expr);

err = -EOPNOTSUPP; - if (!(priv->expr->ops->type->flags & NFT_EXPR_STATEFUL)) - goto err1; - if (priv->expr->ops->type->flags & NFT_EXPR_GC) { if (set->flags & NFT_SET_TIMEOUT) goto err1;