[PATCH v2 bpf 1/2] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

[PATCH v2 bpf 1/2] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

[Matt Bobrowski]

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.

Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
---
 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 = &regs[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;
 
 			if (reg->type == CONST_PTR_TO_DYNPTR)
 				dynptr_arg_type |= MEM_RDONLY;
-- 
2.45.2.741.gdbec12cfda-goog

[PATCH v2 bpf 2/2] bpf: add new negative selftests to cover missing check_func_arg_reg_off() and reg->type check

[Matt Bobrowski]

Add new negative selftests which are intended to cover the
out-of-bounds memory access that could be performed on a
CONST_PTR_TO_DYNPTR within functions taking a ARG_PTR_TO_DYNPTR |
MEM_RDONLY as an argument, and acceptance of invalid register types
i.e. PTR_TO_BTF_ID within functions taking a ARG_PTR_TO_DYNPTR |
MEM_RDONLY.

Reported-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
---
 .../testing/selftests/bpf/progs/dynptr_fail.c | 24 +++++++++++++++++++
 .../bpf/progs/test_kfunc_dynptr_param.c       |  2 +-
 .../selftests/bpf/progs/user_ringbuf_fail.c   | 22 +++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 66a60bfb5867..ed4bba02c861 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -1686,3 +1686,27 @@ int test_dynptr_skb_small_buff(struct __sk_buff *skb)
 
 	return !!data;
 }
+
+__noinline long global_call_bpf_dynptr(const struct bpf_dynptr *dynptr)
+{
+	long ret = 0;
+	/* Avoid leaving this global function empty to avoid having the compiler
+	 * optimize away the call to this global function.
+	 */
+	__sink(ret);
+	return ret;
+}
+
+SEC("?raw_tp")
+__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
+int test_dynptr_reg_type(void *ctx)
+{
+	struct task_struct *current = NULL;
+	/* R1 should be holding a PTR_TO_BTF_ID, so this shouldn't be a
+	 * reg->type that can be passed to a function accepting a
+	 * ARG_PTR_TO_DYNPTR | MEM_RDONLY. process_dynptr_func() should catch
+	 * this.
+	 */
+	global_call_bpf_dynptr((const struct bpf_dynptr *)current);
+	return 0;
+}
diff --git a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
index 2dde8e3fe4c9..e68667aec6a6 100644
--- a/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
+++ b/tools/testing/selftests/bpf/progs/test_kfunc_dynptr_param.c
@@ -45,7 +45,7 @@ int BPF_PROG(not_valid_dynptr, int cmd, union bpf_attr *attr, unsigned int size)
 }
 
 SEC("?lsm.s/bpf")
-__failure __msg("arg#0 expected pointer to stack or dynptr_ptr")
+__failure __msg("arg#1 expected pointer to stack or const struct bpf_dynptr")
 int BPF_PROG(not_ptr_to_stack, int cmd, union bpf_attr *attr, unsigned int size)
 {
 	unsigned long val = 0;
diff --git a/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c b/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
index 11ab25c42c36..54de0389f878 100644
--- a/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
+++ b/tools/testing/selftests/bpf/progs/user_ringbuf_fail.c
@@ -221,3 +221,25 @@ int user_ringbuf_callback_reinit_dynptr_ringbuf(void *ctx)
 	bpf_user_ringbuf_drain(&user_ringbuf, try_reinit_dynptr_ringbuf, NULL, 0);
 	return 0;
 }
+
+__noinline long global_call_bpf_dynptr_data(struct bpf_dynptr *dynptr)
+{
+	bpf_dynptr_data(dynptr, 0xA, 0xA);
+	return 0;
+}
+
+static long callback_adjust_bpf_dynptr_reg_off(struct bpf_dynptr *dynptr,
+					       void *ctx)
+{
+	global_call_bpf_dynptr_data(dynptr += 1024);
+	return 0;
+}
+
+SEC("?raw_tp")
+__failure __msg("dereference of modified dynptr_ptr ptr R1 off=16384 disallowed")
+int user_ringbuf_callback_const_ptr_to_dynptr_reg_off(void *ctx)
+{
+	bpf_user_ringbuf_drain(&user_ringbuf,
+			       callback_adjust_bpf_dynptr_reg_off, NULL, 0);
+	return 0;
+}
-- 
2.45.2.741.gdbec12cfda-goog

Re: [PATCH v2 bpf 1/2] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

[Alexei Starovoitov]

On Mon, Jun 24, 2024 at 11:29 PM Matt Bobrowski
<mattbobrowski@google.com> 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@gmail.com>
> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> Acked-by: Eduard Zingerman <eddyz87@gmail.com>
> Signed-off-by: Matt Bobrowski <mattbobrowski@google.com>
> ---
>  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 = &regs[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.

Re: [PATCH v2 bpf 1/2] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Tue, 25 Jun 2024 06:28:56 +0000 you 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.
> 
> [...]

Here is the summary with links:
  - [v2,bpf,1/2] bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds memory accesses
    https://git.kernel.org/bpf/bpf-next/c/ec2b9a5e11e5
  - [v2,bpf,2/2] bpf: add new negative selftests to cover missing check_func_arg_reg_off() and reg->type check
    https://git.kernel.org/bpf/bpf-next/c/aa293983d202

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html