From b0d0c96dadefface6828bd75be28ec9b0818f8e5 Mon Sep 17 00:00:00 2001 From: Ilias Apalodimas Date: Thu, 11 Nov 2021 16:29:17 +0800 Subject: [PATCH] skbuff: Fix a potential race while recycling page_pool packets mainline inclusion from mainline-v5.14-rc3 commit 2cc3aeb5eccc category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I4CVS3 CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=2cc3aeb5eccc ---------------------------------------------------------------------- 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 Suggested-by: Alexander Duyck Reviewed-by: Alexander Duyck Acked-by: Jesper Dangaard Brouer Signed-off-by: Ilias Apalodimas Signed-off-by: David S. Miller Reviewed-by: Yongxin Li Signed-off-by: Junxin Chen Signed-off-by: Zheng Zengkai --- net/core/skbuff.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index e7bf21d7d531..f73ea11c0874 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -616,7 +616,7 @@ 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); @@ -627,6 +627,17 @@ 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; } /* -- GitLab