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[54.240.197.231]) by smtp.gmail.com with ESMTPSA id fl21-20020a05600c0b9500b00414674a1a40sm3244029wmb.45.2024.03.22.07.38.33 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2024 07:38:33 -0700 (PDT) From: Puranjay Mohan To: Alexei Starovoitov , Daniel Borkmann , John Fastabend , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Paul Walmsley , Palmer Dabbelt , Albert Ou , bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org Cc: puranjay12@gmail.com Subject: [PATCH bpf] bpf: verifier: fix NULL pointer dereference in do_misc_fixups() Date: Fri, 22 Mar 2024 14:38:29 +0000 Message-Id: <20240322143829.40808-1-puranjay12@gmail.com> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: bpf@iogearbox.net The addr_space_cast instruction is convered to a normal 32 bit mov by the verifier if the cast from as(0) to as(1) or if the user has set the flag BPF_F_NO_USER_CONV in the arena. If the BPF program doesn't have an associated arena env->prog->aux->arena is NULL and the verifier currently doesn't check for it being NULL before accessing map_flags. This can cause a NULL pointer dereference: root@rv-tester:~# ./reproducer Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000000000030 Oops [#1] Modules linked in: sch_fq_codel drm fuse i2c_core drm_panel_orientation_quirks backlight configfs ip_tables x_tables CPU: 2 PID: 265 Comm: reproducer Not tainted 6.8.0 #3 Hardware name: riscv-virtio,qemu (DT) epc : do_misc_fixups+0x43c/0x1168 ra : bpf_check+0xda8/0x22b6 epc : ffffffff8017eeaa ra : ffffffff801936d6 sp : ff200000011bb890 gp : ffffffff82293468 tp : ff60000084fcb840 t0 : ff60000084e38048 t1 : 0000000000000048 t2 : ff5fffff80000000 s0 : ff200000011bba60 s1 : ff2000000101d058 a0 : ff6000008b980000 a1 : 0000000000000004 a2 : 00000000000000e1 a3 : 0000000000000001 a4 : 0000000000010000 a5 : 0000000000000000 a6 : 0000000000000001 a7 : ff2000000101d000 s2 : 0000000000000002 s3 : 0000000000000000 s4 : 0000000000000000 s5 : 0000000000000002 s6 : 0000000000000000 s7 : ff6000008b980aa0 s8 : 0000000000010005 s9 : 0000000000000004 s10: ff6000008b980000 s11: 0000000000000000 t3 : 0000000000002000 t4 : 0000ff0000000000 t5 : 00ff000000000000 t6 : ff20000000000000 status: 0000000200000120 badaddr: 0000000000000030 cause: 000000000000000d [] do_misc_fixups+0x43c/0x1168 [] bpf_check+0xda8/0x22b6 [] bpf_prog_load+0x486/0x8dc [] __sys_bpf+0xbd8/0x214e [] __riscv_sys_bpf+0x22/0x2a [] do_trap_ecall_u+0x102/0x17c [] ret_from_exception+0x0/0x64 Code: b345 9783 0024 4685 8b63 16d7 3783 008d 7f9c 7fdc (5b9c) 83c9 ---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Fatal exception SMP: stopping secondary CPUs Add a check for NULL pointer before checking map_flags. Fixes: 6082b6c328b5 ("bpf: Recognize addr_space_cast instruction in the verifier.") Reported-by: xingwei lee Reported-by: yue sun Closes: https://lore.kernel.org/bpf/CABOYnLz09O1+2gGVJuCxd_24a-7UueXzV-Ff+Fr+h5EKFDiYCQ@mail.gmail.com/ Signed-off-by: Puranjay Mohan --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ca6cacf7b42f..78945e7b856d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -19607,7 +19607,8 @@ static int do_misc_fixups(struct bpf_verifier_env *env) for (i = 0; i < insn_cnt;) { if (insn->code == (BPF_ALU64 | BPF_MOV | BPF_X) && insn->imm) { if ((insn->off == BPF_ADDR_SPACE_CAST && insn->imm == 1) || - (((struct bpf_map *)env->prog->aux->arena)->map_flags & BPF_F_NO_USER_CONV)) { + (env->prog->aux->arena && + (((struct bpf_map *)env->prog->aux->arena)->map_flags & BPF_F_NO_USER_CONV))) { /* convert to 32-bit mov that clears upper 32-bit */ insn->code = BPF_ALU | BPF_MOV | BPF_X; /* clear off, so it's a normal 'wX = wY' from JIT pov */