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Mon, 12 Aug 2024 11:30:25 -0700 (PDT) Received: from [192.168.0.235] ([38.34.87.7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2d1c9c5e053sm8838414a91.2.2024.08.12.11.30.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Aug 2024 11:30:24 -0700 (PDT) Message-ID: <0b305ca5045a1adceec313b20f912f9666c1705c.camel@gmail.com> Subject: Re: [PATCH bpf 1/2] bpf: Fix a kernel verifier crash in stacksafe() From: Eduard Zingerman To: Yonghong Song , Alexei Starovoitov Cc: bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Kernel Team , Martin KaFai Lau , Daniel Hodges Date: Mon, 12 Aug 2024 11:30:19 -0700 In-Reply-To: References: <20240812052106.3980303-1-yonghong.song@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.52.3 (3.52.3-1.fc40) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2024-08-12 at 11:26 -0700, Yonghong Song wrote: [...] >=20 > We could do the following to avoid double comparison: diff --git=20 > a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index=20 > df3be12096cf..1906798f1a3d 100644 --- a/kernel/bpf/verifier.c +++=20 > b/kernel/bpf/verifier.c @@ -17338,10 +17338,13 @@ static bool=20 > stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old, */= =20 > for (i =3D 0; i < old->allocated_stack; i++) { struct bpf_reg_state=20 > *old_reg, *cur_reg; + bool cur_exceed_bound; spi =3D i / BPF_REG_SIZE; -= =20 > if (exact !=3D NOT_EXACT && + cur_exceed_bound =3D i >=3D=20 > cur->allocated_stack; + + if (exact !=3D NOT_EXACT && !cur_exceed_bound &= &=20 > old->stack[spi].slot_type[i % BPF_REG_SIZE] !=3D=20 > cur->stack[spi].slot_type[i % BPF_REG_SIZE]) return false; @@ -17363,7= =20 > +17366,7 @@ static bool stacksafe(struct bpf_verifier_env *env, struct= =20 > bpf_func_state *old, /* explored stack has more populated slots than=20 > current stack * and these slots were used */ - if (i >=3D=20 > cur->allocated_stack) + if (cur_exceed_bound) return false; /* 64-bit=20 > scalar spill vs all slots MISC and vice versa. WDYT? >=20 Yonghong, something went wrong with formatting of the above email, could you please resend?