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skbuff: revert "skbuff: remove some unnecessary operation in skb_segment_list()"

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the commit 1ddc3229ad ("skbuff: remove some unnecessary operation
in skb_segment_list()") introduces an issue very similar to the
one already fixed by commit 53475c5dd8 ("net: fix use-after-free when
UDP GRO with shared fraglist").

If the GSO skb goes though skb_clone() and pskb_expand_head() before
entering skb_segment_list(), the latter  will unshare the frag_list
skbs and will release the old list. With the reverted commit in place,
when skb_segment_list() completes, skb->next points to the just
released list, and later on the kernel will hit UaF.

Note that since commit e0e3070a9b ("udp: properly complete L4 GRO
over UDP tunnel packet") the critical scenario can be reproduced also
receiving UDP over vxlan traffic with:

NIC (NETIF_F_GRO_FRAGLIST enabled) -> vxlan -> UDP sink

Attaching a packet socket to the NIC will cause skb_clone() and the
tunnel decapsulation will call pskb_expand_head().

Fixes: 1ddc3229ad ("skbuff: remove some unnecessary operation in skb_segment_list()")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Paolo Abeni 2021-04-14 12:48:48 +02:00 committed by David S. Miller
parent 73d7de66aa
commit 17c3df7078
1 changed files with 12 additions and 3 deletions
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15
net/core/skbuff.c
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@ -3773,13 +3773,13 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
unsigned int tnl_hlen = skb_tnl_header_len(skb);
unsigned int delta_truesize = 0;
unsigned int delta_len = 0;
struct sk_buff *tail = NULL;
struct sk_buff *nskb, *tmp;
int err;
skb_push(skb, -skb_network_offset(skb) + offset);
skb_shinfo(skb)->frag_list = NULL;
skb->next = list_skb;
do {
nskb = list_skb;
@ -3797,8 +3797,17 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
}
}
if (unlikely(err))
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;
delta_truesize += nskb->truesize;
@ -3825,7 +3834,7 @@ struct sk_buff *skb_segment_list(struct sk_buff *skb,
skb_gso_reset(skb);
skb->prev = nskb;
skb->prev = tail;
if (skb_needs_linearize(skb, features) &&
__skb_linearize(skb))