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authorIlias Apalodimas <ilias.apalodimas@linaro.org>2021-07-16 10:02:18 +0300
committerDavid S. Miller <davem@davemloft.net>2021-07-16 11:37:00 -0700
commit2cc3aeb5ecccec0d266813172fcd82b4b5fa5803 (patch)
tree2f8486b71126e60458c257fd72c0561a8e68b8e6 /net
parent20192d9c9f6ae447c461285c915502ffbddf5696 (diff)
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skbuff: Fix a potential race while recycling page_pool packets
As Alexander points out, when we are trying to recycle a cloned/expanded SKB we might trigger a race. The recycling code relies on the pp_recycle bit to trigger, which we carry over to cloned SKBs. If that cloned SKB gets expanded or if we get references to the frags, call skb_release_data() and overwrite skb->head, we are creating separate instances accessing the same page frags. Since the skb_release_data() will first try to recycle the frags, there's a potential race between the original and cloned SKB, since both will have the pp_recycle bit set. Fix this by explicitly those SKBs not recyclable. The atomic_sub_return effectively limits us to a single release case, and when we are calling skb_release_data we are also releasing the option to perform the recycling, or releasing the pages from the page pool. Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling") Reported-by: Alexander Duyck <alexanderduyck@fb.com> Suggested-by: Alexander Duyck <alexanderduyck@fb.com> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com> Acked-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/skbuff.c13
1 files changed, 12 insertions, 1 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index f63de967ac25..0fe97d660790 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -663,7 +663,7 @@ static void skb_release_data(struct sk_buff *skb)
if (skb->cloned &&
atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
&shinfo->dataref))
- return;
+ goto exit;
skb_zcopy_clear(skb, true);
@@ -674,6 +674,17 @@ static void skb_release_data(struct sk_buff *skb)
kfree_skb_list(shinfo->frag_list);
skb_free_head(skb);
+exit:
+ /* When we clone an SKB we copy the reycling bit. The pp_recycle
+ * bit is only set on the head though, so in order to avoid races
+ * while trying to recycle fragments on __skb_frag_unref() we need
+ * to make one SKB responsible for triggering the recycle path.
+ * So disable the recycling bit if an SKB is cloned and we have
+ * additional references to to the fragmented part of the SKB.
+ * Eventually the last SKB will have the recycling bit set and it's
+ * dataref set to 0, which will trigger the recycling
+ */
+ skb->pp_recycle = 0;
}
/*