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([2405:201:682f:389d:941b:5f:cbd3:6ba]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2a3e3cc8d81sm33297085ad.81.2026.01.06.18.10.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Jan 2026 18:10:47 -0800 (PST) From: Deepanshu Kartikey To: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, a.s.protopopov@gmail.com Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Deepanshu Kartikey , syzbot+2c29addf92581b410079@syzkaller.appspotmail.com Subject: [PATCH] bpf: Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() Date: Wed, 7 Jan 2026 07:40:37 +0530 Message-ID: <20260107021037.289644-1-kartikey406@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit BPF_MAP_TYPE_INSN_ARRAY maps store instruction pointers in their ips array, not string data. The map_direct_value_addr callback for this map type returns the address of the ips array, which is not suitable for use as a constant string argument. When a BPF program passes a pointer to an insn_array map value as ARG_PTR_TO_CONST_STR (e.g., to bpf_snprintf), the verifier's null-termination check in check_reg_const_str() operates on the wrong memory region, and at runtime bpf_bprintf_prepare() can read out of bounds searching for a null terminator. Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() since this map type is not designed to hold string data. Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079 Tested-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com Fixes: 493d9e0d6083 ("bpf, x86: add support for indirect jumps") Signed-off-by: Deepanshu Kartikey --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index f0ca69f888fa..3135643d5695 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -9609,6 +9609,11 @@ static int check_reg_const_str(struct bpf_verifier_env *env, if (reg->type != PTR_TO_MAP_VALUE) return -EINVAL; + if (map->map_type == BPF_MAP_TYPE_INSN_ARRAY) { + verbose(env, "R%d points to insn_array map which cannot be used as const string\n", regno); + return -EACCES; + } + if (!bpf_map_is_rdonly(map)) { verbose(env, "R%d does not point to a readonly map'\n", regno); return -EACCES; -- 2.43.0