On Mon, Feb 1, 2021 at 8:09 AM Marco Elver <el...@google.com> wrote: > > Avoid the assumption that ksize(kmalloc(S)) == ksize(kmalloc(S)): when > cloning an skb, save and restore truesize after pskb_expand_head(). This > can occur if the allocator decides to service an allocation of the same > size differently (e.g. use a different size class, or pass the > allocation on to KFENCE). > > Because truesize is used for bookkeeping (such as sk_wmem_queued), a > modified truesize of a cloned skb may result in corrupt bookkeeping and > relevant warnings (such as in sk_stream_kill_queues()). > > Link: https://lkml.kernel.org/r/X9JR/j6dmmoy1...@elver.google.com > Reported-by: syzbot+7b99aafdcc2eedea6...@syzkaller.appspotmail.com > Suggested-by: Eric Dumazet <eduma...@google.com> > Signed-off-by: Marco Elver <el...@google.com> > --- > net/core/skbuff.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 2af12f7e170c..3787093239f5 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -3289,7 +3289,19 @@ EXPORT_SYMBOL(skb_split); > */ > static int skb_prepare_for_shift(struct sk_buff *skb) > { > - return skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC); > + int ret = 0; > + > + if (skb_cloned(skb)) { > + /* Save and restore truesize: pskb_expand_head() may > reallocate > + * memory where ksize(kmalloc(S)) != ksize(kmalloc(S)), but we > + * cannot change truesize at this point. > + */ > + unsigned int save_truesize = skb->truesize; > + > + ret = pskb_expand_head(skb, 0, 0, GFP_ATOMIC); > + skb->truesize = save_truesize; > + } > + return ret;
just a few days ago we found out that this also fixes a syzkaller issue on MPTCP (https://github.com/multipath-tcp/mptcp_net-next/issues/136). I confirmed that this patch fixes the issue for us as well: Tested-by: Christoph Paasch <christoph.paa...@gmail.com> > } > > /** > > base-commit: 14e8e0f6008865d823a8184a276702a6c3cbef3d > -- > 2.30.0.365.g02bc693789-goog >
