From a593f70831b68740fb7db69e0556ca72dac8c7a8 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 17 May 2018 14:06:35 -0700 Subject: bpf: sockmap update rollback on error can incorrectly dec prog refcnt If the user were to only attach one of the parse or verdict programs then it is possible a subsequent sockmap update could incorrectly decrement the refcnt on the program. This happens because in the rollback logic, after an error, we have to decrement the program reference count when its been incremented. However, we only increment the program reference count if the user has both a verdict and a parse program. The reason for this is because, at least at the moment, both are required for any one to be meaningful. The problem fixed here is in the rollback path we decrement the program refcnt even if only one existing. But we never incremented the refcnt in the first place creating an imbalance. This patch fixes the error path to handle this case. Fixes: 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support") Reported-by: Daniel Borkmann Signed-off-by: John Fastabend Acked-by: Martin KaFai Lau Signed-off-by: Daniel Borkmann --- kernel/bpf/sockmap.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'kernel/bpf/sockmap.c') diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c index 098eca568c2b..f03aaa8daadd 100644 --- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c @@ -1717,10 +1717,10 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops, if (tx_msg) { tx_msg = bpf_prog_inc_not_zero(stab->bpf_tx_msg); if (IS_ERR(tx_msg)) { - if (verdict) - bpf_prog_put(verdict); - if (parse) + if (parse && verdict) { bpf_prog_put(parse); + bpf_prog_put(verdict); + } return PTR_ERR(tx_msg); } } @@ -1805,10 +1805,10 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops, out_free: smap_release_sock(psock, sock); out_progs: - if (verdict) - bpf_prog_put(verdict); - if (parse) + if (parse && verdict) { bpf_prog_put(parse); + bpf_prog_put(verdict); + } if (tx_msg) bpf_prog_put(tx_msg); write_unlock_bh(&sock->sk_callback_lock); -- cgit From 9617456054a6160f5e11e892b713fade78aea2e9 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 17 May 2018 14:06:40 -0700 Subject: bpf: parse and verdict prog attach may race with bpf map update In the sockmap design BPF programs (SK_SKB_STREAM_PARSER, SK_SKB_STREAM_VERDICT and SK_MSG_VERDICT) are attached to the sockmap map type and when a sock is added to the map the programs are used by the socket. However, sockmap updates from both userspace and BPF programs can happen concurrently with the attach and detach of these programs. To resolve this we use the bpf_prog_inc_not_zero and a READ_ONCE() primitive to ensure the program pointer is not refeched and possibly NULL'd before the refcnt increment. This happens inside a RCU critical section so although the pointer reference in the map object may be NULL (by a concurrent detach operation) the reference from READ_ONCE will not be free'd until after grace period. This ensures the object returned by READ_ONCE() is valid through the RCU criticl section and safe to use as long as we "know" it may be free'd shortly. Daniel spotted a case in the sock update API where instead of using the READ_ONCE() program reference we used the pointer from the original map, stab->bpf_{verdict|parse|txmsg}. The problem with this is the logic checks the object returned from the READ_ONCE() is not NULL and then tries to reference the object again but using the above map pointer, which may have already been NULL'd by a parallel detach operation. If this happened bpf_porg_inc_not_zero could dereference a NULL pointer. Fix this by using variable returned by READ_ONCE() that is checked for NULL. Fixes: 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support") Reported-by: Daniel Borkmann Signed-off-by: John Fastabend Acked-by: Martin KaFai Lau Signed-off-by: Daniel Borkmann --- kernel/bpf/sockmap.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'kernel/bpf/sockmap.c') diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c index f03aaa8daadd..95a84b2f10ce 100644 --- a/kernel/bpf/sockmap.c +++ b/kernel/bpf/sockmap.c @@ -1703,11 +1703,11 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops, * we increment the refcnt. If this is the case abort with an * error. */ - verdict = bpf_prog_inc_not_zero(stab->bpf_verdict); + verdict = bpf_prog_inc_not_zero(verdict); if (IS_ERR(verdict)) return PTR_ERR(verdict); - parse = bpf_prog_inc_not_zero(stab->bpf_parse); + parse = bpf_prog_inc_not_zero(parse); if (IS_ERR(parse)) { bpf_prog_put(verdict); return PTR_ERR(parse); @@ -1715,7 +1715,7 @@ static int sock_map_ctx_update_elem(struct bpf_sock_ops_kern *skops, } if (tx_msg) { - tx_msg = bpf_prog_inc_not_zero(stab->bpf_tx_msg); + tx_msg = bpf_prog_inc_not_zero(tx_msg); if (IS_ERR(tx_msg)) { if (parse && verdict) { bpf_prog_put(parse); -- cgit