Re: [PATCH net] esp: do not unref managed frag pages in esp_ssg_unref()

On Sun, Jul 12, 2026 at 06:05:30PM +0100, Maher Azzouzi wrote:

esp_ssg_unref() releases the page references held on the source
scatterlist after the AEAD operation completes.  It calls
skb_page_unref() on every frag page for an out-of-place transform
(req->src != req->dst), and in the error path of esp_output_tail()
(already_unref == true) on the request's own scatterlist.

This is wrong when the skb carries managed frags
(SKBFL_MANAGED_FRAG_REFS).  Managed frags are owned by a zerocopy ubuf
and the skb does not hold a per-frag page reference; io_uring SEND_ZC
with a registered buffer attaches the bvec pages this way via
io_sg_from_iter().  The rest of the stack honours this invariant:
skb_release_data() skips the per-frag unref when SKBFL_MANAGED_FRAG_REFS
is set, and skb_zcopy_managed() is the guard used at the other unref
sites.

esp_ssg_unref() is missing that guard, so for a managed-frag skb it
drops a page reference the skb never acquired.  This can underflow the
page reference count and free a page that is still in use.

Guard the function with skb_zcopy_managed() so both unref paths are
skipped for managed-frag skbs, matching skb_release_data().

Fixes: cac2661c53f3 ("esp4: Avoid skb_cow_data whenever possible")
Fixes: 03e2a30f6a27 ("esp6: Avoid skb_cow_data whenever possible")
Signed-off-by: Maher Azzouzi <redacted>

Applied to the ipsec tree, thanks a lot!