From 55667441c84fa5e0911a0aac44fb059c15ba6da2 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Tue, 22 Oct 2019 07:57:46 -0700 Subject: net/flow_dissector: switch to siphash UDP IPv6 packets auto flowlabels are using a 32bit secret (static u32 hashrnd in net/core/flow_dissector.c) and apply jhash() over fields known by the receivers. Attackers can easily infer the 32bit secret and use this information to identify a device and/or user, since this 32bit secret is only set at boot time. Really, using jhash() to generate cookies sent on the wire is a serious security concern. Trying to change the rol32(hash, 16) in ip6_make_flowlabel() would be a dead end. Trying to periodically change the secret (like in sch_sfq.c) could change paths taken in the network for long lived flows. Let's switch to siphash, as we did in commit df453700e8d8 ("inet: switch IP ID generator to siphash") Using a cryptographically strong pseudo random function will solve this privacy issue and more generally remove other weak points in the stack. Packet schedulers using skb_get_hash_perturb() benefit from this change. Fixes: b56774163f99 ("ipv6: Enable auto flow labels by default") Fixes: 42240901f7c4 ("ipv6: Implement different admin modes for automatic flow labels") Fixes: 67800f9b1f4e ("ipv6: Call skb_get_hash_flowi6 to get skb->hash in ip6_make_flowlabel") Fixes: cb1ce2ef387b ("ipv6: Implement automatic flow label generation on transmit") Signed-off-by: Eric Dumazet Reported-by: Jonathan Berger Reported-by: Amit Klein Reported-by: Benny Pinkas Cc: Tom Herbert Signed-off-by: David S. Miller --- include/linux/skbuff.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux/skbuff.h') diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 7914fdaf4226..a391147c03d4 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1354,7 +1354,8 @@ static inline __u32 skb_get_hash_flowi6(struct sk_buff *skb, const struct flowi6 return skb->hash; } -__u32 skb_get_hash_perturb(const struct sk_buff *skb, u32 perturb); +__u32 skb_get_hash_perturb(const struct sk_buff *skb, + const siphash_key_t *perturb); static inline __u32 skb_get_hash_raw(const struct sk_buff *skb) { -- cgit v1.3-18-gd494 From d7d16a89350ab263484c0aa2b523dd3a234e4a80 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 23 Oct 2019 22:44:48 -0700 Subject: net: add skb_queue_empty_lockless() Some paths call skb_queue_empty() without holding the queue lock. We must use a barrier in order to not let the compiler do strange things, and avoid KCSAN splats. Adding a barrier in skb_queue_empty() might be overkill, I prefer adding a new helper to clearly identify points where the callers might be lockless. This might help us finding real bugs. The corresponding WRITE_ONCE() should add zero cost for current compilers. Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- include/linux/skbuff.h | 33 ++++++++++++++++++++++++--------- 1 file changed, 24 insertions(+), 9 deletions(-) (limited to 'include/linux/skbuff.h') diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index a391147c03d4..64a395c7f689 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -1495,6 +1495,19 @@ static inline int skb_queue_empty(const struct sk_buff_head *list) return list->next == (const struct sk_buff *) list; } +/** + * skb_queue_empty_lockless - check if a queue is empty + * @list: queue head + * + * Returns true if the queue is empty, false otherwise. + * This variant can be used in lockless contexts. + */ +static inline bool skb_queue_empty_lockless(const struct sk_buff_head *list) +{ + return READ_ONCE(list->next) == (const struct sk_buff *) list; +} + + /** * skb_queue_is_last - check if skb is the last entry in the queue * @list: queue head @@ -1848,9 +1861,11 @@ static inline void __skb_insert(struct sk_buff *newsk, struct sk_buff *prev, struct sk_buff *next, struct sk_buff_head *list) { - newsk->next = next; - newsk->prev = prev; - next->prev = prev->next = newsk; + /* see skb_queue_empty_lockless() for the opposite READ_ONCE() */ + WRITE_ONCE(newsk->next, next); + WRITE_ONCE(newsk->prev, prev); + WRITE_ONCE(next->prev, newsk); + WRITE_ONCE(prev->next, newsk); list->qlen++; } @@ -1861,11 +1876,11 @@ static inline void __skb_queue_splice(const struct sk_buff_head *list, struct sk_buff *first = list->next; struct sk_buff *last = list->prev; - first->prev = prev; - prev->next = first; + WRITE_ONCE(first->prev, prev); + WRITE_ONCE(prev->next, first); - last->next = next; - next->prev = last; + WRITE_ONCE(last->next, next); + WRITE_ONCE(next->prev, last); } /** @@ -2006,8 +2021,8 @@ static inline void __skb_unlink(struct sk_buff *skb, struct sk_buff_head *list) next = skb->next; prev = skb->prev; skb->next = skb->prev = NULL; - next->prev = prev; - prev->next = next; + WRITE_ONCE(next->prev, prev); + WRITE_ONCE(prev->next, next); } /** -- cgit v1.3-18-gd494