[PATCH 5.15.y 2/2] bpf: Reject fragmented frames in devmap

[Sasha Levin <sashal@kernel.org>]

From: Zhao Zhang <zzhan461@ucr.edu>

[ Upstream commit aa496720618f1a6054f1c870bf10b4f6c99bf656 ]

Devmap broadcast redirects clone the packet for all but the last
destination.

For native XDP, that clone path copies only the linear xdp_frame data,
while fragmented frames keep skb_shared_info in tailroom outside the
linear area. Cloning such a frame leaves XDP_FLAGS_HAS_FRAGS set but
without valid frag metadata, and the later free path can interpret
uninitialized tail data as skb_shared_info, leading to an out-of-bounds
access during frame return.

Reject fragmented native XDP frames in dev_map_enqueue_clone().

Add the same restriction to the generic XDP clone path in
dev_map_redirect_clone(). Generic XDP represents fragmented packets as
nonlinear skbs, and rejecting them here keeps clone-based broadcast
support aligned between native and generic XDP.

Fixes: e624d4ed4aa8 ("xdp: Extend xdp_redirect_map with broadcast support")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:GPT-5.4
Signed-off-by: Zhao Zhang <zzhan461@ucr.edu>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/21c2d153dd25603d359069a02bf06779b51f6423.1780385378.git.zzhan461@ucr.edu
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/bpf/devmap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 6ad4b068abc770..713e2627850a47 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -551,6 +551,10 @@ static int dev_map_enqueue_clone(struct bpf_dtab_netdev *obj,
 {
 	struct xdp_frame *nxdpf;
 
+	/* Frags live outside the linear frame and cannot be cloned safely. */
+	if (unlikely(xdp_frame_has_frags(xdpf)))
+		return -EOPNOTSUPP;
+
 	nxdpf = xdpf_clone(xdpf);
 	if (!nxdpf)
 		return -ENOMEM;
@@ -696,6 +700,9 @@ static int dev_map_redirect_clone(struct bpf_dtab_netdev *dst,
 	struct sk_buff *nskb;
 	int err;
 
+	if (unlikely(skb_is_nonlinear(skb)))
+		return -EOPNOTSUPP;
+
 	nskb = skb_clone(skb, GFP_ATOMIC);
 	if (!nskb)
 		return -ENOMEM;
-- 
2.53.0