[PATCH bpf v3] bpf: Fix NULL pointer dereference in bpf_sk_storage_clone and diag paths

[Weiming Shi <bestswngs@gmail.com>]

bpf_selem_unlink_nofail() sets SDATA(selem)->smap to NULL before
removing the selem from the storage hlist. A concurrent RCU reader in
bpf_sk_storage_clone() can observe the selem still on the list with
smap already NULL, causing a NULL pointer dereference.

 general protection fault, probably for non-canonical address 0xdffffc000000000a:
 KASAN: null-ptr-deref in range [0x0000000000000050-0x0000000000000057]
 RIP: 0010:bpf_sk_storage_clone+0x1cd/0xaa0 net/core/bpf_sk_storage.c:174
 Call Trace:
  <IRQ>
  sk_clone+0xfed/0x1980 net/core/sock.c:2591
  inet_csk_clone_lock+0x30/0x760 net/ipv4/inet_connection_sock.c:1222
  tcp_create_openreq_child+0x35/0x2680 net/ipv4/tcp_minisocks.c:571
  tcp_v4_syn_recv_sock+0x123/0xf90 net/ipv4/tcp_ipv4.c:1729
  tcp_check_req+0x8e1/0x2580 include/net/tcp.h:855
  tcp_v4_rcv+0x1845/0x3b80 net/ipv4/tcp_ipv4.c:2347

Add a NULL check for smap in bpf_sk_storage_clone().
bpf_sk_storage_diag_put_all() and bpf_sk_storage_diag_put() have the
same unprotected dereference pattern, add NULL checks there as well and
pass the validated smap to diag_get() so it no longer performs its own
rcu_dereference.

Fixes: 5d800f87d0a5 ("bpf: Support lockless unlink when freeing map or local storage")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
v3:
  pass smap to diag_get()
v2:
  drop the NULL check in diag_get(); The caller already checks smap for
NULL.

 net/core/bpf_sk_storage.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c
index f8338acebf077..1f9bd0005883b 100644
--- a/net/core/bpf_sk_storage.c
+++ b/net/core/bpf_sk_storage.c
@@ -172,7 +172,7 @@ int bpf_sk_storage_clone(const struct sock *sk, struct sock *newsk)
 		struct bpf_map *map;
 
 		smap = rcu_dereference(SDATA(selem)->smap);
-		if (!(smap->map.map_flags & BPF_F_CLONE))
+		if (!smap || !(smap->map.map_flags & BPF_F_CLONE))
 			continue;
 
 		/* Note that for lockless listeners adding new element
@@ -534,10 +534,10 @@ bpf_sk_storage_diag_alloc(const struct nlattr *nla_stgs)
 }
 EXPORT_SYMBOL_GPL(bpf_sk_storage_diag_alloc);
 
-static int diag_get(struct bpf_local_storage_data *sdata, struct sk_buff *skb)
+static int diag_get(struct bpf_local_storage_map *smap,
+		    struct bpf_local_storage_data *sdata, struct sk_buff *skb)
 {
 	struct nlattr *nla_stg, *nla_value;
-	struct bpf_local_storage_map *smap;
 
 	/* It cannot exceed max nlattr's payload */
 	BUILD_BUG_ON(U16_MAX - NLA_HDRLEN < BPF_LOCAL_STORAGE_MAX_VALUE_SIZE);
@@ -546,7 +546,6 @@ static int diag_get(struct bpf_local_storage_data *sdata, struct sk_buff *skb)
 	if (!nla_stg)
 		return -EMSGSIZE;
 
-	smap = rcu_dereference(sdata->smap);
 	if (nla_put_u32(skb, SK_DIAG_BPF_STORAGE_MAP_ID, smap->map.id))
 		goto errout;
 
@@ -599,9 +598,11 @@ static int bpf_sk_storage_diag_put_all(struct sock *sk, struct sk_buff *skb,
 	saved_len = skb->len;
 	hlist_for_each_entry_rcu(selem, &sk_storage->list, snode) {
 		smap = rcu_dereference(SDATA(selem)->smap);
+		if (!smap)
+			continue;
 		diag_size += nla_value_size(smap->map.value_size);
 
-		if (nla_stgs && diag_get(SDATA(selem), skb))
+		if (nla_stgs && diag_get(smap, SDATA(selem), skb))
 			/* Continue to learn diag_size */
 			err = -EMSGSIZE;
 	}
@@ -633,6 +634,7 @@ int bpf_sk_storage_diag_put(struct bpf_sk_storage_diag *diag,
 	unsigned int diag_size = nla_total_size(0);
 	struct bpf_local_storage *sk_storage;
 	struct bpf_local_storage_data *sdata;
+	struct bpf_local_storage_map *smap;
 	struct nlattr *nla_stgs;
 	unsigned int saved_len;
 	int err = 0;
@@ -668,7 +670,11 @@ int bpf_sk_storage_diag_put(struct bpf_sk_storage_diag *diag,
 
 		diag_size += nla_value_size(diag->maps[i]->value_size);
 
-		if (nla_stgs && diag_get(sdata, skb))
+		smap = rcu_dereference(sdata->smap);
+		if (!smap)
+			continue;
+
+		if (nla_stgs && diag_get(smap, sdata, skb))
 			/* Continue to learn diag_size */
 			err = -EMSGSIZE;
 	}
-- 
2.43.0