From 414776621d1006e57e80e6db7fdc3837897aaa64 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Wed, 7 Aug 2019 17:03:59 -0700 Subject: net/tls: prevent skb_orphan() from leaking TLS plain text with offload sk_validate_xmit_skb() and drivers depend on the sk member of struct sk_buff to identify segments requiring encryption. Any operation which removes or does not preserve the original TLS socket such as skb_orphan() or skb_clone() will cause clear text leaks. Make the TCP socket underlying an offloaded TLS connection mark all skbs as decrypted, if TLS TX is in offload mode. Then in sk_validate_xmit_skb() catch skbs which have no socket (or a socket with no validation) and decrypted flag set. Note that CONFIG_SOCK_VALIDATE_XMIT, CONFIG_TLS_DEVICE and sk->sk_validate_xmit_skb are slightly interchangeable right now, they all imply TLS offload. The new checks are guarded by CONFIG_TLS_DEVICE because that's the option guarding the sk_buff->decrypted member. Second, smaller issue with orphaning is that it breaks the guarantee that packets will be delivered to device queues in-order. All TLS offload drivers depend on that scheduling property. This means skb_orphan_partial()'s trick of preserving partial socket references will cause issues in the drivers. We need a full orphan, and as a result netem delay/throttling will cause all TLS offload skbs to be dropped. Reusing the sk_buff->decrypted flag also protects from leaking clear text when incoming, decrypted skb is redirected (e.g. by TC). See commit 0608c69c9a80 ("bpf: sk_msg, sock{map|hash} redirect through ULP") for justification why the internal flag is safe. The only location which could leak the flag in is tcp_bpf_sendmsg(), which is taken care of by clearing the previously unused bit. v2: - remove superfluous decrypted mark copy (Willem); - remove the stale doc entry (Boris); - rely entirely on EOR marking to prevent coalescing (Boris); - use an internal sendpages flag instead of marking the socket (Boris). v3 (Willem): - reorganize the can_skb_orphan_partial() condition; - fix the flag leak-in through tcp_bpf_sendmsg. Signed-off-by: Jakub Kicinski Acked-by: Willem de Bruijn Reviewed-by: Boris Pismenny Signed-off-by: David S. Miller --- include/linux/skbuff.h | 8 ++++++++ include/linux/socket.h | 3 +++ include/net/sock.h | 10 +++++++++- 3 files changed, 20 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index d8af86d995d6..ba5583522d24 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1374,6 +1374,14 @@ static inline void skb_copy_hash(struct sk_buff *to, const struct sk_buff *from) to->l4_hash = from->l4_hash; }; +static inline void skb_copy_decrypted(struct sk_buff *to, + const struct sk_buff *from) +{ +#ifdef CONFIG_TLS_DEVICE + to->decrypted = from->decrypted; +#endif +} + #ifdef NET_SKBUFF_DATA_USES_OFFSET static inline unsigned char *skb_end_pointer(const struct sk_buff *skb) { diff --git a/include/linux/socket.h b/include/linux/socket.h index 97523818cb14..fc0bed59fc84 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -292,6 +292,9 @@ struct ucred { #define MSG_BATCH 0x40000 /* sendmmsg(): more messages coming */ #define MSG_EOF MSG_FIN #define MSG_NO_SHARED_FRAGS 0x80000 /* sendpage() internal : page frags are not shared */ +#define MSG_SENDPAGE_DECRYPTED 0x100000 /* sendpage() internal : page may carry + * plain text and require encryption + */ #define MSG_ZEROCOPY 0x4000000 /* Use user data in kernel path */ #define MSG_FASTOPEN 0x20000000 /* Send data in TCP SYN */ diff --git a/include/net/sock.h b/include/net/sock.h index 228db3998e46..2c53f1a1d905 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2482,6 +2482,7 @@ static inline bool sk_fullsock(const struct sock *sk) /* Checks if this SKB belongs to an HW offloaded socket * and whether any SW fallbacks are required based on dev. + * Check decrypted mark in case skb_orphan() cleared socket. */ static inline struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb, struct net_device *dev) @@ -2489,8 +2490,15 @@ static inline struct sk_buff *sk_validate_xmit_skb(struct sk_buff *skb, #ifdef CONFIG_SOCK_VALIDATE_XMIT struct sock *sk = skb->sk; - if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb) + if (sk && sk_fullsock(sk) && sk->sk_validate_xmit_skb) { skb = sk->sk_validate_xmit_skb(sk, dev, skb); +#ifdef CONFIG_TLS_DEVICE + } else if (unlikely(skb->decrypted)) { + pr_warn_ratelimited("unencrypted skb with no associated socket - dropping\n"); + kfree_skb(skb); + skb = NULL; +#endif + } #endif return skb; -- cgit v1.2.3