propagate shared-frag marker through" failed to apply to 5.15-stable tree (original) (raw)

* FAILED: patch "[PATCH] net: skbuff: propagate shared-frag marker through" failed to apply to 5.15-stable tree @ 2026-05-22 7:39 gregkh 2026-05-22 19:46 ` [PATCH 5.15] net: skbuff: propagate shared-frag marker through frag-transfer helpers Ben Hutchings 0 siblings, 1 reply; 3+ messages in thread From: gregkh @ 2026-05-22 7:39 UTC (permalink / raw) To: imv4bel, aaron1esau, ben, malin89, pabeni, rajat.gupta, sd, sultan, tanjingguo Cc: stable

The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 48f6a5356a33dd78e7144ae1faef95ffc990aae0

<resolve conflicts, build, test, etc.>

git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2026052230-kilogram-proving-cd58@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 48f6a5356a33dd78e7144ae1faef95ffc990aae0 Mon Sep 17 00:00:00 2001 From: Hyunwoo Kim imv4bel@gmail.com Date: Sat, 16 May 2026 07:28:53 +0900 Subject: [PATCH] net: skbuff: propagate shared-frag marker through frag-transfer helpers

Two frag-transfer helpers (__pskb_copy_fclone() and skb_shift()) fail to propagate the SKBFL_SHARED_FRAG bit in skb_shinfo()->flags when moving frags from source to destination. _pskb_copy_fclone() defers the rest of the shinfo metadata to skb_copy_header() after copying frag descriptors, but that helper only carries over gso{size,segs, type} and never touches skb_shinfo()->flags; skb_shift() moves frag descriptors directly and leaves flags untouched. As a result, the destination skb keeps a reference to the same externally-owned or page-cache-backed pages while reporting skb_has_shared_frag() as false.

The mismatch is harmful in any in-place writer that uses skb_has_shared_frag() to decide whether shared pages must be detoured through skb_cow_data(). ESP input is one such writer (esp4.c, esp6.c), and a single nft 'dup to ' rule -- or any other nf_dup_ipv4() / xt_TEE caller -- is enough to land a pskb_copy()'d skb in esp_input() with the marker stripped, letting an unprivileged user write into the page cache of a root-owned read-only file via authencesn-ESN stray writes.

Set SKBFL_SHARED_FRAG on the destination whenever frag descriptors were actually moved from the source. skb_copy() and skb_copy_expand() share skb_copy_header() too but linearize all paged data into freshly allocated head storage and emerge with nr_frags == 0, so skb_has_shared_frag() returns false on its own; they need no change.

The same omission exists in skb_gro_receive() and skb_gro_receive_list(). The former moves the incoming skb's frag descriptors into the accumulator's last sub-skb via two paths (a direct frag-move loop and the head_frag + memcpy path); the latter chains the incoming skb whole onto p's frag_list. Downstream skb_segment() reads only skb_shinfo(p)->flags, and skb_segment_list() reuses each sub-skb's shinfo as the nskb -- both p and lp must carry the marker.

The same omission also exists in tcp_clone_payload(), which builds an MTU probe skb by moving frag descriptors from skbs on sk_write_queue into a freshly allocated nskb. The helper falls into the same family and warrants the same fix for consistency; no TCP TX-side in-place writer is currently known to reach a user page through this gap, but a future consumer depending on the marker would regress silently.

The same omission exists in skb_segment(): the per-iteration flag merge takes only head_skb's flag, and the inner switch that rebinds frag_skb to list_skb on head_skb-frags exhaustion does not fold the new frag_skb's flag into nskb. Fold frag_skb's flag at both sites so segments drawing frags from frag_list members carry the marker.

Fixes: cef401de7be8 ("net: fix possible wrong checksum generation") Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags") Suggested-by: Sabrina Dubroca sd@queasysnail.net Suggested-by: Sultan Alsawaf sultan@kerneltoast.com Suggested-by: Ben Hutchings ben@decadent.org.uk Suggested-by: Lin Ma malin89@huawei.com Suggested-by: Jingguo Tan tanjingguo@huawei.com Suggested-by: Aaron Esau aaron1esau@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Hyunwoo Kim imv4bel@gmail.com Tested-by: Rajat Gupta rajat.gupta@oss.qualcomm.com Link: https://patch.msgid.link/ageeJfJHwgzmKXbh@v4bel Signed-off-by: Paolo Abeni pabeni@redhat.com

diff --git a/net/core/gro.c b/net/core/gro.c index 31d21de5b15a..9f8960789b2c 100644 --- a/net/core/gro.c +++ b/net/core/gro.c @@ -213,10 +213,12 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) p->data_len += len; p->truesize += delta_truesize; p->len += len; + skb_shinfo(p)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; if (lp != p) { lp->data_len += len; lp->truesize += delta_truesize; lp->len += len; + skb_shinfo(lp)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; } NAPI_GRO_CB(skb)->same_flow = 1; return 0; @@ -244,6 +246,8 @@ int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) p->truesize += skb->truesize; p->len += skb->len;

diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 9c4e8d331d6d..44ac121cfccb 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -2248,6 +2248,7 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom, skb_frag_ref(skb, i); } skb_shinfo(n)->nr_frags = i; + skb_shinfo(n)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG; }

 if (skb_has_frag_list(skb)) {

@@ -4349,6 +4350,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen) tgt->ip_summed = CHECKSUM_PARTIAL; skb->ip_summed = CHECKSUM_PARTIAL;

@@ -4959,7 +4962,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_copy_from_linear_data_offset(head_skb, offset, skb_put(nskb, hsize), hsize);

@@ -4976,6 +4980,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags; frag_skb = list_skb; + + skb_shinfo(nskb)->flags |= skb_shinfo(frag_skb)->flags & SKBFL_SHARED_FRAG; + if (!skb_headlen(list_skb)) { BUG_ON(!nfrags); } else { diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index f9d8755705f7..6e4bb411dc04 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -2626,6 +2626,7 @@ static int tcp_clone_payload(struct sock *sk, struct sk_buff *to, todo = min_t(int, skb_frag_size(fragfrom), probe_size - len); len += todo; + skb_shinfo(to)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG; if (lastfrag && skb_frag_page(fragfrom) == skb_frag_page(lastfrag) && skb_frag_off(fragfrom) == skb_frag_off(lastfrag) +

^ permalink raw reply related [flat|nested] 3+ messages in thread


* [PATCH 5.15] net: skbuff: propagate shared-frag marker through frag-transfer helpers 2026-05-22 7:39 FAILED: patch "[PATCH] net: skbuff: propagate shared-frag marker through" failed to apply to 5.15-stable tree gregkh **@ 2026-05-22 19:46 Ben Hutchings** 2026-05-23 6:04 Harshit Mogalapalli 0 siblings, 1 reply; 3+ messages in thread From: Ben Hutchings @ 2026-05-22 19:46 UTC (permalink / raw) To: gregkh Cc: imv4bel, aaron1esau, ben, malin89, pabeni, rajat.gupta, sd, sultan, tanjingguo, stable

[-- Attachment #1: Type: text/plain, Size: 6103 bytes --]

From: Hyunwoo Kim imv4bel@gmail.com

commit 48f6a5356a33dd78e7144ae1faef95ffc990aae0 upstream.

Two frag-transfer helpers (__pskb_copy_fclone() and skb_shift()) fail to propagate the SKBFL_SHARED_FRAG bit in skb_shinfo()->flags when moving frags from source to destination. _pskb_copy_fclone() defers the rest of the shinfo metadata to skb_copy_header() after copying frag descriptors, but that helper only carries over gso{size,segs, type} and never touches skb_shinfo()->flags; skb_shift() moves frag descriptors directly and leaves flags untouched. As a result, the destination skb keeps a reference to the same externally-owned or page-cache-backed pages while reporting skb_has_shared_frag() as false.

The mismatch is harmful in any in-place writer that uses skb_has_shared_frag() to decide whether shared pages must be detoured through skb_cow_data(). ESP input is one such writer (esp4.c, esp6.c), and a single nft 'dup to ' rule -- or any other nf_dup_ipv4() / xt_TEE caller -- is enough to land a pskb_copy()'d skb in esp_input() with the marker stripped, letting an unprivileged user write into the page cache of a root-owned read-only file via authencesn-ESN stray writes.

Set SKBFL_SHARED_FRAG on the destination whenever frag descriptors were actually moved from the source. skb_copy() and skb_copy_expand() share skb_copy_header() too but linearize all paged data into freshly allocated head storage and emerge with nr_frags == 0, so skb_has_shared_frag() returns false on its own; they need no change.

The same omission exists in skb_gro_receive() and skb_gro_receive_list(). The former moves the incoming skb's frag descriptors into the accumulator's last sub-skb via two paths (a direct frag-move loop and the head_frag + memcpy path); the latter chains the incoming skb whole onto p's frag_list. Downstream skb_segment() reads only skb_shinfo(p)->flags, and skb_segment_list() reuses each sub-skb's shinfo as the nskb -- both p and lp must carry the marker.

The same omission also exists in tcp_clone_payload(), which builds an MTU probe skb by moving frag descriptors from skbs on sk_write_queue into a freshly allocated nskb. The helper falls into the same family and warrants the same fix for consistency; no TCP TX-side in-place writer is currently known to reach a user page through this gap, but a future consumer depending on the marker would regress silently.

The same omission exists in skb_segment(): the per-iteration flag merge takes only head_skb's flag, and the inner switch that rebinds frag_skb to list_skb on head_skb-frags exhaustion does not fold the new frag_skb's flag into nskb. Fold frag_skb's flag at both sites so segments drawing frags from frag_list members carry the marker.

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 aadb87aa5e7e..a8d09eff26f1 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1661,6 +1661,7 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom, skb_frag_ref(skb, i); } skb_shinfo(n)->nr_frags = i; + skb_shinfo(n)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG; }

 if (skb_has_frag_list(skb)) {

@@ -3650,6 +3651,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen) tgt->ip_summed = CHECKSUM_PARTIAL; skb->ip_summed = CHECKSUM_PARTIAL;

@@ -4017,6 +4020,8 @@ int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) p->truesize += skb->truesize; p->len += skb->len;

@@ -4251,7 +4256,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_copy_from_linear_data_offset(head_skb, offset, skb_put(nskb, hsize), hsize);

@@ -4268,6 +4274,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags; frag_skb = list_skb; + + skb_shinfo(nskb)->flags |= skb_shinfo(frag_skb)->flags & SKBFL_SHARED_FRAG; + if (!skb_headlen(list_skb)) { BUG_ON(!nfrags); } else { @@ -4490,10 +4499,12 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) p->data_len += len; p->truesize += delta_truesize; p->len += len; + skb_shinfo(p)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; if (lp != p) { lp->data_len += len; lp->truesize += delta_truesize; lp->len += len; + skb_shinfo(lp)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; } NAPI_GRO_CB(skb)->same_flow = 1; return 0;

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^ permalink raw reply related [flat|nested] 3+ messages in thread


* Re: [PATCH 5.15] net: skbuff: propagate shared-frag marker through frag-transfer helpers 2026-05-22 19:46 [[PATCH 5.15] net: skbuff: propagate shared-frag marker through frag-transfer helpers](#m3d33daf8cb59a3584bd53fe73b2b933fedad5d30) Ben Hutchings **@ 2026-05-23 6:04 Harshit Mogalapalli** 0 siblings, 0 replies; 3+ messages in thread From: Harshit Mogalapalli @ 2026-05-23 6:04 UTC (permalink / raw) To: Ben Hutchings, gregkh Cc: imv4bel, aaron1esau, ben, malin89, pabeni, rajat.gupta, sd, sultan, tanjingguo, stable

On 23/05/26 01:16, Ben Hutchings wrote:

From: Hyunwoo Kim imv4bel@gmail.com

commit 48f6a5356a33dd78e7144ae1faef95ffc990aae0 upstream.

Two frag-transfer helpers (__pskb_copy_fclone() and skb_shift()) fail to propagate the SKBFL_SHARED_FRAG bit in skb_shinfo()->flags when moving frags from source to destination. _pskb_copy_fclone() defers the rest of the shinfo metadata to skb_copy_header() after copying frag descriptors, but that helper only carries over gso{size,segs, type} and never touches skb_shinfo()->flags; skb_shift() moves frag descriptors directly and leaves flags untouched. As a result, the destination skb keeps a reference to the same externally-owned or page-cache-backed pages while reporting skb_has_shared_frag() as false.

The mismatch is harmful in any in-place writer that uses skb_has_shared_frag() to decide whether shared pages must be detoured through skb_cow_data(). ESP input is one such writer (esp4.c, esp6.c), and a single nft 'dup to ' rule -- or any other nf_dup_ipv4() / xt_TEE caller -- is enough to land a pskb_copy()'d skb in esp_input() with the marker stripped, letting an unprivileged user write into the page cache of a root-owned read-only file via authencesn-ESN stray writes.

Set SKBFL_SHARED_FRAG on the destination whenever frag descriptors were actually moved from the source. skb_copy() and skb_copy_expand() share skb_copy_header() too but linearize all paged data into freshly allocated head storage and emerge with nr_frags == 0, so skb_has_shared_frag() returns false on its own; they need no change.

The same omission exists in skb_gro_receive() and skb_gro_receive_list(). The former moves the incoming skb's frag descriptors into the accumulator's last sub-skb via two paths (a direct frag-move loop and the head_frag + memcpy path); the latter chains the incoming skb whole onto p's frag_list. Downstream skb_segment() reads only skb_shinfo(p)->flags, and skb_segment_list() reuses each sub-skb's shinfo as the nskb -- both p and lp must carry the marker.

The same omission also exists in tcp_clone_payload(), which builds an MTU probe skb by moving frag descriptors from skbs on sk_write_queue into a freshly allocated nskb. The helper falls into the same family and warrants the same fix for consistency; no TCP TX-side in-place writer is currently known to reach a user page through this gap, but a future consumer depending on the marker would regress silently.

The same omission exists in skb_segment(): the per-iteration flag merge takes only head_skb's flag, and the inner switch that rebinds frag_skb to list_skb on head_skb-frags exhaustion does not fold the new frag_skb's flag into nskb. Fold frag_skb's flag at both sites so segments drawing frags from frag_list members carry the marker.

Fixes: cef401de7be8 ("net: fix possible wrong checksum generation") Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags") Suggested-by: Sabrina Dubroca sd@queasysnail.net Suggested-by: Sultan Alsawaf sultan@kerneltoast.com Suggested-by: Ben Hutchings ben@decadent.org.uk Suggested-by: Lin Ma malin89@huawei.com Suggested-by: Jingguo Tan tanjingguo@huawei.com Suggested-by: Aaron Esau aaron1esau@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Hyunwoo Kim imv4bel@gmail.com Tested-by: Rajat Gupta rajat.gupta@oss.qualcomm.com Link: https://patch.msgid.link/ageeJfJHwgzmKXbh@v4bel Signed-off-by: Paolo Abeni pabeni@redhat.com [bwh: Backported to 5.15:

right

right as we don't have commit: 736013292e3c ("tcp: let tcp_mtu_probe() build headless packets")

Right, looks good, as we don't have commit: ede57d58e6f3 ("net: helper function skb_len_add") in 5.15.y

LGTM.

So from a backport point of view.

Reviewed-by: Harshit Mogalapalli harshit.m.mogalapalli@oracle.com

thanks, Harshit

Signed-off-by: Ben Hutchings benh@debian.org

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 aadb87aa5e7e..a8d09eff26f1 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1661,6 +1661,7 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom, skb_frag_ref(skb, i); } skb_shinfo(n)->nr_frags = i; + skb_shinfo(n)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG; }

  if (skb_has_frag_list(skb)) {

@@ -3650,6 +3651,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen) tgt->ip_summed = CHECKSUM_PARTIAL; skb->ip_summed = CHECKSUM_PARTIAL;

@@ -4017,6 +4020,8 @@ int skb_gro_receive_list(struct sk_buff *p, struct sk_buff *skb) p->truesize += skb->truesize; p->len += skb->len;

@@ -4251,7 +4256,8 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, skb_copy_from_linear_data_offset(head_skb, offset, skb_put(nskb, hsize), hsize);

@@ -4268,6 +4274,9 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, nfrags = skb_shinfo(list_skb)->nr_frags; frag = skb_shinfo(list_skb)->frags; frag_skb = list_skb; + + skb_shinfo(nskb)->flags |= skb_shinfo(frag_skb)->flags & SKBFL_SHARED_FRAG; + if (!skb_headlen(list_skb)) { BUG_ON(!nfrags); } else { @@ -4490,10 +4499,12 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) p->data_len += len; p->truesize += delta_truesize; p->len += len; + skb_shinfo(p)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; if (lp != p) { lp->data_len += len; lp->truesize += delta_truesize; lp->len += len; + skb_shinfo(lp)->flags |= skbinfo->flags & SKBFL_SHARED_FRAG; } NAPI_GRO_CB(skb)->same_flow = 1; return 0;

^ permalink raw reply [flat|nested] 3+ messages in thread


end of thread, other threads:[~2026-05-23 6:05 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2026-05-22 7:39 FAILED: patch "[PATCH] net: skbuff: propagate shared-frag marker through" failed to apply to 5.15-stable tree gregkh 2026-05-22 19:46 [[PATCH 5.15] net: skbuff: propagate shared-frag marker through frag-transfer helpers](#m3d33daf8cb59a3584bd53fe73b2b933fedad5d30) Ben Hutchings 2026-05-23 6:04 Harshit Mogalapalli


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