On Mon, Jun 24, 2024 at 11:29 PM Matt Bobrowski
<mattbobrowski@xxxxxxxxxx> wrote:
>
> Currently, it's possible to pass in a modified CONST_PTR_TO_DYNPTR to
> a global function as an argument. The adverse effects of this is that
> BPF helpers can continue to make use of this modified
> CONST_PTR_TO_DYNPTR from within the context of the global function,
> which can unintentionally result in out-of-bounds memory accesses and
> therefore compromise overall system stability i.e.
>
> [ 244.157771] BUG: KASAN: slab-out-of-bounds in bpf_dynptr_data+0x137/0x140
> [ 244.161345] Read of size 8 at addr ffff88810914be68 by task test_progs/302
> [ 244.167151] CPU: 0 PID: 302 Comm: test_progs Tainted: G O E 6.10.0-rc3-00131-g66b586715063 #533
> [ 244.174318] Call Trace:
> [ 244.175787] <TASK>
> [ 244.177356] dump_stack_lvl+0x66/0xa0
> [ 244.179531] print_report+0xce/0x670
> [ 244.182314] ? __virt_addr_valid+0x200/0x3e0
> [ 244.184908] kasan_report+0xd7/0x110
> [ 244.187408] ? bpf_dynptr_data+0x137/0x140
> [ 244.189714] ? bpf_dynptr_data+0x137/0x140
> [ 244.192020] bpf_dynptr_data+0x137/0x140
> [ 244.194264] bpf_prog_b02a02fdd2bdc5fa_global_call_bpf_dynptr_data+0x22/0x26
> [ 244.198044] bpf_prog_b0fe7b9d7dc3abde_callback_adjust_bpf_dynptr_reg_off+0x1f/0x23
> [ 244.202136] bpf_user_ringbuf_drain+0x2c7/0x570
> [ 244.204744] ? 0xffffffffc0009e58
> [ 244.206593] ? __pfx_bpf_user_ringbuf_drain+0x10/0x10
> [ 244.209795] bpf_prog_33ab33f6a804ba2d_user_ringbuf_callback_const_ptr_to_dynptr_reg_off+0x47/0x4b
> [ 244.215922] bpf_trampoline_6442502480+0x43/0xe3
> [ 244.218691] __x64_sys_prlimit64+0x9/0xf0
> [ 244.220912] do_syscall_64+0xc1/0x1d0
> [ 244.223043] entry_SYSCALL_64_after_hwframe+0x77/0x7f
> [ 244.226458] RIP: 0033:0x7ffa3eb8f059
> [ 244.228582] Code: 08 89 e8 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8f 1d 0d 00 f7 d8 64 89 01 48
> [ 244.241307] RSP: 002b:00007ffa3e9c6eb8 EFLAGS: 00000206 ORIG_RAX: 000000000000012e
> [ 244.246474] RAX: ffffffffffffffda RBX: 00007ffa3e9c7cdc RCX: 00007ffa3eb8f059
> [ 244.250478] RDX: 00007ffa3eb162b4 RSI: 0000000000000000 RDI: 00007ffa3e9c7fb0
> [ 244.255396] RBP: 00007ffa3e9c6ed0 R08: 00007ffa3e9c76c0 R09: 0000000000000000
> [ 244.260195] R10: 0000000000000000 R11: 0000000000000206 R12: ffffffffffffff80
> [ 244.264201] R13: 000000000000001c R14: 00007ffc5d6b4260 R15: 00007ffa3e1c7000
> [ 244.268303] </TASK>
>
> Add a check_func_arg_reg_off() to the path in which the BPF verifier
> verifies the arguments of global function arguments, specifically
> those which take an argument of type ARG_PTR_TO_DYNPTR |
> MEM_RDONLY. Also, process_dynptr_func() doesn't appear to perform any
> explicit and strict type matching on the supplied register type, so
> let's also enforce that a register either type PTR_TO_STACK or
> CONST_PTR_TO_DYNPTR is by the caller.
The fix makes sense, but I applied it to bpf-next tree.
Since kfunc_dynptr_nullable_test3 had to be adjusted there.
> Reported-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> Acked-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> Acked-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
> Signed-off-by: Matt Bobrowski <mattbobrowski@xxxxxxxxxx>
> ---
> kernel/bpf/verifier.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 214a9fa8c6fb..fe12463511f6 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -7715,6 +7715,13 @@ static int process_dynptr_func(struct bpf_verifier_env *env, int regno, int insn
> struct bpf_reg_state *regs = cur_regs(env), *reg = ®s[regno];
> int err;
>
> + if (reg->type != PTR_TO_STACK && reg->type != CONST_PTR_TO_DYNPTR) {
> + verbose(env,
> + "arg#%d expected pointer to stack or const struct bpf_dynptr\n",
> + regno);
> + return -EINVAL;
> + }
> +
> /* MEM_UNINIT and MEM_RDONLY are exclusive, when applied to an
> * ARG_PTR_TO_DYNPTR (or ARG_PTR_TO_DYNPTR | DYNPTR_TYPE_*):
> */
> @@ -9464,6 +9471,10 @@ static int btf_check_func_arg_match(struct bpf_verifier_env *env, int subprog,
> return -EINVAL;
> }
> } else if (arg->arg_type == (ARG_PTR_TO_DYNPTR | MEM_RDONLY)) {
> + ret = check_func_arg_reg_off(env, reg, regno, ARG_PTR_TO_DYNPTR);
> + if (ret)
> + return ret;
> +
> ret = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
> if (ret)
> return ret;
> @@ -11954,14 +11965,8 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
> break;
> case KF_ARG_PTR_TO_DYNPTR:
> {
> - enum bpf_arg_type dynptr_arg_type = ARG_PTR_TO_DYNPTR;
> int clone_ref_obj_id = 0;
> -
> - if (reg->type != PTR_TO_STACK &&
> - reg->type != CONST_PTR_TO_DYNPTR) {
> - verbose(env, "arg#%d expected pointer to stack or dynptr_ptr\n", i);
> - return -EINVAL;
> - }
> + enum bpf_arg_type dynptr_arg_type = ARG_PTR_TO_DYNPTR;
also fixed that to keep the original order and
reduce diff noise.
