| Message ID | 20240322143829.40808-1-puranjay12@gmail.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | [bpf] bpf: verifier: fix NULL pointer dereference in do_misc_fixups() | expand |
Puranjay Mohan <puranjay12@gmail.com> writes: > 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 > [<ffffffff8017eeaa>] do_misc_fixups+0x43c/0x1168 > [<ffffffff801936d6>] bpf_check+0xda8/0x22b6 > [<ffffffff80174b32>] bpf_prog_load+0x486/0x8dc > [<ffffffff80176566>] __sys_bpf+0xbd8/0x214e > [<ffffffff80177d14>] __riscv_sys_bpf+0x22/0x2a > [<ffffffff80d2493a>] do_trap_ecall_u+0x102/0x17c > [<ffffffff80d3048c>] 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 <xrivendell7@gmail.com> > Reported-by: yue sun <samsun1006219@gmail.com> > Closes: https://lore.kernel.org/bpf/CABOYnLz09O1+2gGVJuCxd_24a-7UueXzV-Ff+Fr+h5EKFDiYCQ@mail.gmail.com/ > Signed-off-by: Puranjay Mohan <puranjay12@gmail.com> > --- > 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 && Kumar made me aware of the fact that env->prog->aux_arena should never be NULL if the program has an addr_space_cast instruction. This means that rather than checking for the NULL pointer here and leaving the addr_space_cast as it is, We should reject programs that contain an addr_space_cast instruction but don't have an associated arena. Sent v2 doing the above: https://lore.kernel.org/bpf/20240322153518.11555-1-puranjay12@gmail.com/
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 */
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 [<ffffffff8017eeaa>] do_misc_fixups+0x43c/0x1168 [<ffffffff801936d6>] bpf_check+0xda8/0x22b6 [<ffffffff80174b32>] bpf_prog_load+0x486/0x8dc [<ffffffff80176566>] __sys_bpf+0xbd8/0x214e [<ffffffff80177d14>] __riscv_sys_bpf+0x22/0x2a [<ffffffff80d2493a>] do_trap_ecall_u+0x102/0x17c [<ffffffff80d3048c>] 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 <xrivendell7@gmail.com> Reported-by: yue sun <samsun1006219@gmail.com> Closes: https://lore.kernel.org/bpf/CABOYnLz09O1+2gGVJuCxd_24a-7UueXzV-Ff+Fr+h5EKFDiYCQ@mail.gmail.com/ Signed-off-by: Puranjay Mohan <puranjay12@gmail.com> --- kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)