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Bump version to 6.12.0-124.56.3

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net: skbuff: propagate shared-frag marker through frag-transfer helpers

Replace 124.56.2's partial fix (which was a backport of Hyunwoo Kim's
v1 patch covering only __pskb_copy_fclone() and skb_try_coalesce())
with a backport of the upstream v3 patch:
https://lore.kernel.org/all/agW4vC0r8QOUKtRT@v4bel/

v3 also covers skb_shift() (the new hunk added in v2) and
skb_gro_receive() / skb_gro_receive_list() (the audit follow-up
suggested by Sultan Alsawaf in agVpIsaSherjHTYg@sultan-box).

All five sites moved frag descriptors between skbs without
propagating the SKBFL_SHARED_FRAG marker, so destinations could end
up referencing externally-owned or page-cache-backed pages while
reporting skb_has_shared_frag() as false. Combined with ESP-over-UDP
and UDP GRO, or any nf_dup_ipv4 / xt_TEE caller, this lets an
unprivileged user trigger in-place ESP decryption over root-owned
page-cache pages (CVE-2026-46300, "Fragnesia").
This commit is contained in:
eabdullin 2026-05-14 14:28:05 +03:00
parent c3f0a68cfa
commit 42132178bc
2 changed files with 71 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

90
1100-net-skbuff-propagate-shared-frag-marker.patch
View File

@ -1,27 +1,28 @@
From: Andrew Lukoshko <alukoshko@almalinux.org>
Subject: [PATCH AlmaLinux 10] net: skbuff: propagate shared-frag marker through pskb_copy()
From: Eduard Abdullin <eabdullin@almalinux.org>
Subject: [PATCH AlmaLinux 10] net: skbuff: propagate shared-frag marker through frag-transfer helpers
Backport of upstream patch posted at
https://lore.kernel.org/all/agRfuVOeMI5pbHhY@v4bel/
(sibling to the xfrm/esp shared-frag fix upstream commit f4c50a4034e6,
already merged into 6.12.0-124.56.1 via the c10s import).
Backport of upstream v3 patch posted at
https://lore.kernel.org/all/agW4vC0r8QOUKtRT@v4bel/
(sibling to upstream commit f4c50a4034e6 "xfrm: esp: avoid in-place
decrypt on shared skb frags", already part of 6.12.0-124.56.1 via the
c10s import).
__pskb_copy_fclone() shallow-copies the source's frag descriptors and
bumps each page's refcount via skb_frag_ref(), then defers the rest
of the shinfo metadata to skb_copy_header(). That helper only carries
over gso_{size,segs,type} and never touches skb_shinfo()->flags, so
the destination skb keeps a reference to the same externally-owned or
page-cache-backed pages while reporting skb_has_shared_frag() as
false.
Three frag-transfer helpers (__pskb_copy_fclone(), skb_try_coalesce(),
and skb_shift()) and the GRO accumulator helpers (skb_gro_receive()
and skb_gro_receive_list()) fail to propagate the SKBFL_SHARED_FRAG
bit in skb_shinfo()->flags when moving frag descriptors from source
to destination. 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 <local>' 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.
esp6.c). Combined with an nft 'dup to <local>' rule, an
nf_dup_ipv4() / xt_TEE caller, or ESP-over-UDP with UDP GRO, this
lets an unprivileged user write into the page cache of a root-owned
read-only file via authencesn-ESN stray writes (CVE-2026-46300,
"Fragnesia").
Set SKBFL_SHARED_FRAG on the destination whenever frag descriptors
were actually moved from the source. skb_copy() and skb_copy_expand()
@ -29,18 +30,50 @@ 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.
Verified to apply with `patch -p1 -F0` (no offset, no fuzz, no rejects)
against kernel-6.12.0-124.56.1.el10_1.
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 plus a
"merge:" fallback that chains the whole skb onto frag_list; 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.
Fixes: cef401de7be8 ("net: fix possible wrong checksum generation")
Fixes: f4c50a4034e6 ("xfrm: esp: avoid in-place decrypt on shared skb frags")
Reported-by: Sultan Alsawaf <sultan@kerneltoast.com>
Reported-by: William Bowling <vakzz@zellic.io>
Reported-by: Hyunwoo Kim <imv4bel@gmail.com>
Signed-off-by: Andrew Lukoshko <alukoshko@almalinux.org>
Signed-off-by: Eduard Abdullin <eabdullin@almalinux.org>
---
net/core/skbuff.c | 3 +++
1 file changed, 3 insertions(+)
net/core/gro.c | 4 ++++
net/core/skbuff.c | 5 +++++
2 files changed, 9 insertions(+)
--- 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;
+ skb_shinfo(p)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG;
+
NAPI_GRO_CB(skb)->same_flow = 1;
return 0;
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2123,6 +2123,7 @@ struct sk_buff *__pskb_copy_fclone(struct sk_buff *skb, int headroom,
@ -51,7 +84,16 @@ Signed-off-by: Andrew Lukoshko <alukoshko@almalinux.org>
}
if (skb_has_frag_list(skb)) {
@@ -6028,6 +6029,8 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
@@ -4198,6 +4199,8 @@ int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen)
tgt->ip_summed = CHECKSUM_PARTIAL;
skb->ip_summed = CHECKSUM_PARTIAL;
+ skb_shinfo(tgt)->flags |= skb_shinfo(skb)->flags & SKBFL_SHARED_FRAG;
+
skb_len_add(skb, -shiftlen);
skb_len_add(tgt, shiftlen);
@@ -6028,6 +6031,8 @@ bool skb_try_coalesce(struct sk_buff *to, struct sk_buff *from,
from_shinfo->frags,
from_shinfo->nr_frags * sizeof(skb_frag_t));
to_shinfo->nr_frags += from_shinfo->nr_frags;

7
kernel.spec
View File

@ -176,13 +176,13 @@ Summary: The Linux kernel
%define specrpmversion 6.12.0
%define specversion 6.12.0
%define patchversion 6.12
%define pkgrelease 124.56.2
%define pkgrelease 124.56.3
%define kversion 6
%define tarfile_release 6.12.0-124.56.1.el10_1
# This is needed to do merge window version magic
%define patchlevel 12
# This allows pkg_release to have configurable %%{?dist} tag
%define specrelease 124.56.2%{?buildid}%{?dist}
%define specrelease 124.56.3%{?buildid}%{?dist}
# This defines the kabi tarball version
%define kabiversion 6.12.0-124.56.1.el10_1
@ -4379,6 +4379,9 @@ fi\
#
#
%changelog
* Thu May 14 2026 Eduard Abdullin <eabdullin@almalinux.org> - 6.12.0-124.56.3
- net: skbuff: propagate shared-frag marker through frag-transfer helpers
* Wed May 13 2026 Andrew Lukoshko <alukoshko@almalinux.org> - 6.12.0-124.56.2
- net: skbuff: propagate shared-frag marker through pskb_copy()