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Sun, 26 Apr 2026 12:17:08 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@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 Date: Sun, 26 Apr 2026 15:17:08 -0400 Message-Id: To: "Junyoung Jang" , , , , , Cc: , , , , , , , Subject: Re: [PATCH bpf v2] bpf: Fix off-by-one boundary validation in arena direct-value access From: "Emil Tsalapatis" X-Mailer: aerc 0.21.0-0-g5549850facc2 References: <2026042614-scowling-hankie-f84b@gregkh> <20260426172505.1947915-1-graypanda.inzag@gmail.com> In-Reply-To: <20260426172505.1947915-1-graypanda.inzag@gmail.com> On Sun Apr 26, 2026 at 1:25 PM EDT, Junyoung Jang wrote: > BPF_MAP_TYPE_ARENA accepts BPF_PSEUDO_MAP_VALUE offsets at exactly > the end of the arena mapping (off =3D=3D arena_size). The boundary check > in arena_map_direct_value_addr() uses `>` instead of `>=3D`, which > incorrectly allows a one-past-end pointer to be accepted. > > Change the condition to `>=3D` to correctly reject offsets that fall > outside the valid arena user_vm range. > > Fixes: 317460317a02 ("bpf: Introduce bpf_arena.") > Signed-off-by: Junyoung Jang > --- Reviewed-by: Emil Tsalapatis > kernel/bpf/arena.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c > index 802656c6fd3c..49a8f7b1beef 100644 > --- a/kernel/bpf/arena.c > +++ b/kernel/bpf/arena.c > @@ -511,7 +511,7 @@ static int arena_map_direct_value_addr(const struct b= pf_map *map, u64 *imm, u32 > { > struct bpf_arena *arena =3D container_of(map, struct bpf_arena, map); > =20 > - if ((u64)off > arena->user_vm_end - arena->user_vm_start) > + if ((u64)off >=3D arena->user_vm_end - arena->user_vm_start) > return -ERANGE; > *imm =3D (unsigned long)arena->user_vm_start; > return 0;