[PATCH v4.9.y] netfilter: nf_tables: disallow non-stateful expression in sets earlier

[PATCH v4.9.y] netfilter: nf_tables: disallow non-stateful expression in sets earlier

[Ajay Kaher]

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 v4.9.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 ec460ae..0aad9b8 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1756,23 +1756,27 @@ 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:
 	module_put(info.ops->type->owner);
-err1:
+err_expr_parse:
 	return ERR_PTR(err);
 }
 
diff --git a/net/netfilter/nft_dynset.c b/net/netfilter/nft_dynset.c
index 81adbfa..5c25ffe 100644
--- a/net/netfilter/nft_dynset.c
+++ b/net/netfilter/nft_dynset.c
@@ -196,9 +196,6 @@ static int nft_dynset_init(const struct nft_ctx *ctx,
 		if (IS_ERR(priv->expr))
 			return PTR_ERR(priv->expr);
 
-		err = -EOPNOTSUPP;
-		if (!(priv->expr->ops->type->flags & NFT_EXPR_STATEFUL))
-			goto err1;
 	} else if (set->flags & NFT_SET_EVAL)
 		return -EINVAL;
 
-- 
2.7.4

Re: [PATCH v4.9.y] netfilter: nf_tables: disallow non-stateful expression in sets earlier

[Greg KH]

On Tue, Jun 07, 2022 at 09:55:21AM +0530, Ajay Kaher wrote:
> 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 v4.9.y]
> Signed-off-by: Ajay Kaher <akaher@vmware.com>

Both now queued up, thanks.

greg k-h