Messages in this thread Patch in this message | | | From | Ilias Apalodimas <> | Subject | [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets | Date | Fri, 9 Jul 2021 09:29:39 +0300 |
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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 skbb_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> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org> --- Changes since v1: - Set the recycle bit to 0 during skb_release_data instead of the individual fucntions triggering the issue, in order to catch all cases net/core/skbuff.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 12aabcda6db2..f91f09a824be 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 +674,8 @@ static void skb_release_data(struct sk_buff *skb) kfree_skb_list(shinfo->frag_list); skb_free_head(skb); +exit: + skb->pp_recycle = 0; } /* -- 2.32.0.rc0
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