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Miller" Cc: Jakub Kicinski , Paolo Abeni , Eric Dumazet , David Ahern , Alexey Kuznetsov , Willem de Bruijn , Willem de Bruijn , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Maoyi Xie Subject: [PATCH net v8 0/2] ipv6: flowlabel: per-netns budget for unprivileged callers Date: Wed, 6 May 2026 16:24:14 +0800 Message-Id: <20260506082416.2259567-1-maoyixie.tju@gmail.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Maoyi Xie This series fixes the cross-tenant DoS in net/ipv6/ip6_flowlabel.c. v1 through v6 were single-patch postings, each in its own thread. v6 review pointed out that the existing fl_size read in mem_check() and the corresponding write in fl_intern() are not in the same critical section. v7 split the work into 2 patches. Patch 1/2 is a prerequisite. It moves spin_lock_bh(&ip6_fl_lock) and the matching unlock from fl_intern() into its only caller ipv6_flowlabel_get(), so the mem_check() call runs under the same critical section as the fl_intern() insert. With all writers and the read of fl_size under the lock, fl_size is converted from atomic_t to plain int. This is independent of the per-netns budget. It also makes 2/2 backportable without conflicts. Patch 2/2 is the v6 patch, rebased on 1/2. - flowlabel_count is plain int rather than atomic_t, since the previous patch put all writers and readers under ip6_fl_lock. - In ip6_fl_gc(), fl_free() is now placed below the fl_size and flowlabel_count decrements, removing the v6 cache of fl->fl_net. - In ip6_fl_purge(), fl_free() stays in its original position. The function argument net is used for flowlabel_count. - mem_check() uses spaces around the / operator on all four expressions, addressing the checkpatch note in v6 review. Numeric budget (preserved from v6): pre-patch: global non-CAP_NET_ADMIN budget = FL_MAX_SIZE - FL_MAX_SIZE/4 = 4096 - 1024 = 3072 per-actor reach = 3072 post-patch: FL_MAX_SIZE doubled to 8192 global non-CAP_NET_ADMIN budget = 8192 - 2048 = 6144 per-netns ceiling = 6144 / 2 = 3072 per-actor reach = 3072 (preserved) CAP_NET_ADMIN against init_user_ns still bypasses both caps. Reproducer (KASAN VM, 4 cores, qemu): unprivileged netns A holds 3072 flowlabels via 100 procs. Fresh unprivileged netns B then allocates 32 flowlabels (the FL_MAX_PER_SOCK ceiling for one socket), the same as a clean baseline. Without the per-netns ceiling, netns A could push fl_size past FL_MAX_SIZE - FL_MAX_SIZE / 4 and netns B would see allocations denied. v8: - 1/2: replaced the "Caller must hold ip6_fl_lock" comment in fl_intern() with lockdep_assert_held(&ip6_fl_lock), matching the runtime check already used in mem_check(), per Willem's review. - 1/2: added Fixes: 1da177e4c3f4 trailer to match 2/2, per Willem's review. - Carried forward Reviewed-by: Willem de Bruijn on both patches. - No code change beyond the lockdep_assert_held swap. v7: - 2-patch series: 1/2 (lock prep) and 2/2 (v6 rebased on 1/2). - 2/2: flowlabel_count int, fl_free() reorder removed in ip6_fl_purge(), checkpatch / spacing in mem_check() fixed. v6: rebased onto current net (resolves the conflict on include/net/netns/ipv6.h that v5 hit). fl_free() restored to its pre-series position, with fl->fl_net cached locally in ip6_fl_gc(). v5: replaced the per-netns ceiling FL_MAX_SIZE/8 with the computed unpriv_user_limit = (FL_MAX_SIZE - FL_MAX_SIZE/4)/2, which evaluates to 3072. v4: addressed Willem's v3 review on netdev. Dropped the flowlabel_has_excl cacheline argument in favour of "fills the existing 4-byte hole after ipmr_seq". v3: addressed Willem's review on the private security@ thread. Merged FL_MAX_SIZE doubling, dropped test data, moved flowlabel_count near ipmr_seq, inlined fl->fl_net in ip6_fl_gc(). v2: per-netns counter + cap, sent to security@ as a 2-patch series. v1: fix-shape sketch in original disclosure. Maoyi Xie (2): ipv6: flowlabel: take ip6_fl_lock across mem_check and fl_intern ipv6: flowlabel: enforce per-netns limit for unprivileged callers include/net/netns/ipv6.h | 1 + net/ipv6/ip6_flowlabel.c | 46 +++++++++++++++++++++++++++------------- 2 files changed, 32 insertions(+), 15 deletions(-) base-commit: ebb639024ebd47a13a511cce6ae630c15e4b3126 -- 2.34.1