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Date: Thu, 7 Jan 2021 09:39:13 +0900 From: Dongseok Yi <dseok.yi@...sung.com> To: "David S. Miller" <davem@...emloft.net>, Willem de Bruijn <willemb@...gle.com> Cc: Jakub Kicinski <kuba@...nel.org>, Miaohe Lin <linmiaohe@...wei.com>, Paolo Abeni <pabeni@...hat.com>, Florian Westphal <fw@...len.de>, Al Viro <viro@...iv.linux.org.uk>, Guillaume Nault <gnault@...hat.com>, Yunsheng Lin <linyunsheng@...wei.com>, Steffen Klassert <steffen.klassert@...unet.com>, Yadu Kishore <kyk.segfault@...il.com>, Marco Elver <elver@...gle.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, namkyu78.kim@...sung.com, Dongseok Yi <dseok.yi@...sung.com> Subject: [PATCH net v2] net: fix use-after-free when UDP GRO with shared fraglist skbs in fraglist could be shared by a BPF filter loaded at TC. It triggers skb_ensure_writable -> pskb_expand_head -> skb_clone_fraglist -> skb_get on each skb in the fraglist. While tcpdump, sk_receive_queue of PF_PACKET has the original fraglist. But the same fraglist is queued to PF_INET (or PF_INET6) as the fraglist chain made by skb_segment_list. If the new skb (not fraglist) is queued to one of the sk_receive_queue, multiple ptypes can see this. The skb could be released by ptypes and it causes use-after-free. [ 4443.426215] ------------[ cut here ]------------ [ 4443.426222] refcount_t: underflow; use-after-free. [ 4443.426291] WARNING: CPU: 7 PID: 28161 at lib/refcount.c:190 refcount_dec_and_test_checked+0xa4/0xc8 [ 4443.426726] pstate: 60400005 (nZCv daif +PAN -UAO) [ 4443.426732] pc : refcount_dec_and_test_checked+0xa4/0xc8 [ 4443.426737] lr : refcount_dec_and_test_checked+0xa0/0xc8 [ 4443.426808] Call trace: [ 4443.426813] refcount_dec_and_test_checked+0xa4/0xc8 [ 4443.426823] skb_release_data+0x144/0x264 [ 4443.426828] kfree_skb+0x58/0xc4 [ 4443.426832] skb_queue_purge+0x64/0x9c [ 4443.426844] packet_set_ring+0x5f0/0x820 [ 4443.426849] packet_setsockopt+0x5a4/0xcd0 [ 4443.426853] __sys_setsockopt+0x188/0x278 [ 4443.426858] __arm64_sys_setsockopt+0x28/0x38 [ 4443.426869] el0_svc_common+0xf0/0x1d0 [ 4443.426873] el0_svc_handler+0x74/0x98 [ 4443.426880] el0_svc+0x8/0xc Fixes: 3a1296a38d0c (net: Support GRO/GSO fraglist chaining.) Signed-off-by: Dongseok Yi <dseok.yi@...sung.com> Acked-by: Willem de Bruijn <willemb@...gle.com> --- net/core/skbuff.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) v2: Expand the commit message to clarify a BPF filter loaded diff --git a/net/core/skbuff.c b/net/core/skbuff.c index f62cae3..1dcbda8 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3655,7 +3655,8 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb, unsigned int delta_truesize = 0; unsigned int delta_len = 0; struct sk_buff *tail = NULL; - struct sk_buff *nskb; + struct sk_buff *nskb, *tmp; + int err; skb_push(skb, -skb_network_offset(skb) + offset); @@ -3665,11 +3666,28 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb, nskb = list_skb; list_skb = list_skb->next; + err = 0; + if (skb_shared(nskb)) { + tmp = skb_clone(nskb, GFP_ATOMIC); + if (tmp) { + kfree_skb(nskb); + nskb = tmp; + err = skb_unclone(nskb, GFP_ATOMIC); + } else { + err = -ENOMEM; + } + } + if (!tail) skb->next = nskb; else tail->next = nskb; + if (unlikely(err)) { + nskb->next = list_skb; + goto err_linearize; + } + tail = nskb; delta_len += nskb->len; -- 2.7.4
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