| Message ID | 20210716070222.106422-1-ilias.apalodimas@linaro.org |
|---|---|
| State | New |
| Headers | show |
| Series | [1/1,v3] skbuff: Fix a potential race while recycling page_pool packets | expand |
Hello: This patch was applied to netdev/net.git (refs/heads/master): On Fri, 16 Jul 2021 10:02:18 +0300 you wrote: > 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. > > [...] Here is the summary with links: - [1/1,v3] skbuff: Fix a potential race while recycling page_pool packets https://git.kernel.org/netdev/net/c/2cc3aeb5eccc You are awesome, thank you! -- Deet-doot-dot, I am a bot. https://korg.docs.kernel.org/patchwork/pwbot.html
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 12aabcda6db2..8ec5c1136692 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; } /*
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> --- 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 Changes since v2: - Add a comment explaining why we need to reset the recycling bit net/core/skbuff.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) -- 2.32.0.rc0