This is a note to let you know that I've just added the patch titled

skbuff: in skb_copy_ubufs unclone before releasing zerocopy

to the 4.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: skbuff-in-skb_copy_ubufs-unclone-before-releasing-zerocopy.patch and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Sun Dec 31 11:12:48 CET 2017

From: Willem de Bruijn willemb@google.com Date: Thu, 28 Dec 2017 12:38:13 -0500 Subject: skbuff: in skb_copy_ubufs unclone before releasing zerocopy

From: Willem de Bruijn willemb@google.com

skb_copy_ubufs must unclone before it is safe to modify its skb_shared_info with skb_zcopy_clear.

Commit b90ddd568792 ("skbuff: skb_copy_ubufs must release uarg even without user frags") ensures that all skbs release their zerocopy state, even those without frags.

But I forgot an edge case where such an skb arrives that is cloned.

The stack does not build such packets. Vhost/tun skbs have their frags orphaned before cloning. TCP skbs only attach zerocopy state when a frag is added.

But if TCP packets can be trimmed or linearized, this might occur. Tracing the code I found no instance so far (e.g., skb_linearize ends up calling skb_zcopy_clear if !skb->data_len).

Still, it is non-obvious that no path exists. And it is fragile to rely on this.

Fixes: b90ddd568792 ("skbuff: skb_copy_ubufs must release uarg even without user frags") Signed-off-by: Willem de Bruijn willemb@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/skbuff.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1181,12 +1181,12 @@ int skb_copy_ubufs(struct sk_buff *skb, int i, new_frags; u32 d_off;

- if (!num_frags) - goto release; - if (skb_shared(skb) || skb_unclone(skb, gfp_mask)) return -EINVAL;

+ if (!num_frags) + goto release; + new_frags = (__skb_pagelen(skb) + PAGE_SIZE - 1) >> PAGE_SHIFT; for (i = 0; i < new_frags; i++) { page = alloc_page(gfp_mask);

Patches currently in stable-queue which might be from willemb@google.com are

queue-4.14/skbuff-skb_copy_ubufs-must-release-uarg-even-without-user-frags.patch queue-4.14/sock-free-skb-in-skb_complete_tx_timestamp-on-error.patch queue-4.14/skbuff-orphan-frags-before-zerocopy-clone.patch queue-4.14/skbuff-in-skb_copy_ubufs-unclone-before-releasing-zerocopy.patch