bpf: add missing check_func_arg_reg_off() to prevent out-of-bounds me…

…mory accesses 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 torvalds#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. Lastly, we also add a new negative test which catches this regression. Reported-by: Kumar Kartikeya Dwivedi <[email protected]> Signed-off-by: Matt Bobrowski <[email protected]>
intel-lab-lkp · Jun 19, 2024 · 933ee08 · 933ee08
1 parent 66b5867
commit 933ee08
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Showing 3 changed files with 41 additions and 10 deletions.
diff --git 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_*):
 	 */
@@ -9464,7 +9471,13 @@ 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 = process_dynptr_func(env, regno, -1, arg->arg_type, 0);
+			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;
 		} else if (base_type(arg->arg_type) == ARG_PTR_TO_BTF_ID) {
@@ -11954,14 +11967,8 @@ 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;
@@ -11990,7 +11997,9 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 				}
 			}
 
-			ret = process_dynptr_func(env, regno, insn_idx, dynptr_arg_type, clone_ref_obj_id);
+			ret = process_dynptr_func(env, regno, insn_idx,
+						  dynptr_arg_type,
+						  clone_ref_obj_id);
 			if (ret < 0)
 				return ret;
 

diff --git 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
@@ -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;
+}