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Ivanov" To: steffen.klassert@secunet.com, herbert@gondor.apana.org.au, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, saakashkumar@marvell.com Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linux.dev, "Nikola Z. Ivanov" Subject: [PATCH net] net/xfrm: Refuse to allocate xfrm_state with SPI value 0 Date: Sun, 21 Sep 2025 05:27:01 +0300 Message-ID: <20250921022701.530305-1-zlatistiv@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Reported by syzkaller: "KASAN: slab-use-after-free Read in xfrm_alloc_spi" Before commit 94f39804d891 ("xfrm: Duplicate SPI Handling") xfrm_alloc_spi would report spi=3D0 as unavailable. Add this behaviour back by adding 1 to the "low" value when it is passed as= 0. Allocating xfrm_state with spi=3D0 leads to UAF or CPU stall. Fixes: 94f39804d891 ("xfrm: Duplicate SPI Handling") Signed-off-by: Nikola Z. Ivanov --- This should probably be sanitized in verify_spi_info but doing so will change the interface. The bug is easily reploducible by issuing some iproute commands: root@syzkaller:~# ip xfrm state allocspi mode tunnel proto esp src 192.168.= 1.100 dst 192.168.1.200 min 0 max 3 src 192.168.1.100 dst 192.168.1.200 proto esp spi 0x00000001 reqid 0 mode tunnel replay-window 0 anti-replay context: seq 0x0, oseq 0x0, bitmap 0x00000000 sel src 192.168.1.100/32 dst 192.168.1.200/32 root@syzkaller:~# ip xfrm state allocspi mode tunnel proto esp src 192.168.= 1.100 dst 192.168.1.200 min 0 max 3 src 192.168.1.100 dst 192.168.1.200 proto esp spi 0x00000000 reqid 0 mode tunnel replay-window 0 anti-replay context: seq 0x0, oseq 0x0, bitmap 0x00000000 sel src 192.168.1.100/32 dst 192.168.1.200/32 root@syzkaller:~# ip xfrm state allocspi mode tunnel proto esp src 192.168.= 1.100 dst 192.168.1.200 min 0 max 3 src 192.168.1.100 dst 192.168.1.200 proto esp spi 0x00000003 reqid 0 mode tunnel replay-window 0 anti-replay context: seq 0x0, oseq 0x0, bitmap 0x00000000 sel src 192.168.1.100/32 dst 192.168.1.200/32 root@syzkaller:~# ip xfrm state allocspi mode tunnel proto esp src 192.168.= 1.100 dst 192.168.1.200 min 0 max 3 [ 34.267077] rcu: INFO: rcu_preempt self-detected stall on CPU [ 34.267107] rcu: 1-....: (1 GPs behind) idle=3D8b84/1/0x400000000000= 0000 softirq=3D9934/9935 fqs=3D5250 [ 34.269110] rcu: (t=3D21004 jiffies g=3D5953 q=3D571 ncpus=3D2) [ 34.271123] CPU: 1 UID: 0 PID: 296 Comm: ip Not tainted 6.17.0-rc6-00004= -ge6f19f124217-dirty #55 PREEMPT(voluntary) [ 34.271123] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS = 1.17.0-5.fc42 04/01/2014 [ 34.271123] RIP: 0010:xfrm_alloc_spi+0x2d5/0xe60 net/xfrm/xfrm_state.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c index 78fcbb89cf32..4414346a24d7 100644 --- a/net/xfrm/xfrm_state.c +++ b/net/xfrm/xfrm_state.c @@ -2566,7 +2566,9 @@ int xfrm_alloc_spi(struct xfrm_state *x, u32 low, u32= high, unsigned int h; struct xfrm_state *x0; int err =3D -ENOENT; - u32 range =3D high - low + 1; + if (low =3D=3D 0) + low =3D 1; + u32 range =3D high + 1 - low; __be32 newspi =3D 0; =20 spin_lock_bh(&x->lock); --=20 2.51.0