net: skbuff: fix pskb_carve leaking zcopy pages When SKBFL_MANAGED_FRAG_REFS is set, frag pages are not refcounted but their lifetime is controlled by the attached ubuf_info. To make a copy of the skb_shared_info, we either should clear the flag and reference the frags, or keep the flag and have frags unreferenced. pskb_carve_inside_header() and pskb_carve_inside_nonlinear() don't follow the rule and thus can leak page references. Let's clear SKBFL_MANAGED_FRAG_REFS from the original skb to fix it. It's the simplest way to address it, but there are more performant ways to do that if it ever becomes a problem. Link: https://lore.kernel.org/all/20260523085809.26331-1-nvminh232@clc.fitus.edu.vn/ Fixes: 753f1ca4e1e50 ("net: introduce managed frags infrastructure") Reported-by: Minh Nguyen <minhnguyen.080505@gmail.com> Reported-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/1e2086aa69217d7f9c8da3d38f5be7160f1b4cd1.1779993185.git.asml.silence@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 0d3cc11..c02f0a5 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c
@@ -6823,6 +6823,11 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off, skb_copy_from_linear_data_offset(skb, off, data, new_hlen); skb->len -= off; + /* Remove SKBFL_MANAGED_FRAG_REFS instead of trying to honour it + * while refcounting frags below. + */ + skb_zcopy_downgrade_managed(skb); + memcpy((struct skb_shared_info *)(data + size), skb_shinfo(skb), offsetof(struct skb_shared_info, @@ -6936,6 +6941,11 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off, return -ENOMEM; size = SKB_WITH_OVERHEAD(size); + /* Remove SKBFL_MANAGED_FRAG_REFS instead of trying to honour it + * while refcounting frags below. + */ + skb_zcopy_downgrade_managed(skb); + memcpy((struct skb_shared_info *)(data + size), skb_shinfo(skb), offsetof(struct skb_shared_info, frags[0])); if (skb_orphan_frags(skb, gfp_mask)) {