Merge branch 'fix-bpf_loop-syzbot-report'

Kumar Kartikeya Dwivedi says:

====================
Fix bpf_loop syzbot report

Needs Eduard's ack. Fix for the report in
https://lore.kernel.org/bpf/6a9ad24c.b5d4176b.238c3e.0001.GAE@google.com.
====================

Link: https://patch.msgid.link/20260905014735.1452988-1-memxor@gmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>

include/linux/bpf.h

@@ -894,6 +894,7 @@ enum bpf_arg_type {
 
 	ARG_PTR_TO_CTX,		/* pointer to context */
 	ARG_ANYTHING,		/* any (initialized) argument is ok */
+	ARG_SCALAR,		/* scalar argument */
 	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */
 	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock (fullsock) */

kernel/bpf/bpf_iter.c

@@ -754,7 +754,7 @@ const struct bpf_func_proto bpf_loop_proto = {
 	.func		= bpf_loop,
 	.gpl_only	= false,
 	.ret_type	= RET_INTEGER,
-	.arg1_type	= ARG_ANYTHING,
+	.arg1_type	= ARG_SCALAR,
 	.arg2_type	= ARG_PTR_TO_FUNC,
 	.arg3_type	= ARG_PTR_TO_STACK_OR_NULL,
 	.arg4_type	= ARG_ANYTHING,

kernel/bpf/verifier.c

@@ -8211,6 +8211,7 @@ static const struct bpf_reg_types *compatible_reg_types[__BPF_ARG_TYPE_MAX] = {
 	[ARG_MEM_SIZE]			= &scalar_types,
 	[ARG_MEM_SIZE_OR_ZERO]		= &scalar_types,
 	[ARG_CONST_ALLOC_SIZE_OR_ZERO]	= &scalar_types,
+	[ARG_SCALAR]			= &scalar_types,
 	[ARG_CONST_MAP_PTR]		= &const_map_ptr_types,
 	[ARG_PTR_TO_CTX]		= &context_types,
 	[ARG_PTR_TO_SOCK_COMMON]	= &sock_types,

tools/testing/selftests/bpf/progs/verifier_iterating_callbacks.c

@@ -168,6 +168,23 @@ static int iter_limit_cb(__u32 idx, struct num_context *ctx)
 	return 0;
 }
 
+SEC("?raw_tp")
+__failure __msg("R1 type=ctx expected=scalar")
+__naked void bpf_loop_reject_pointer(void)
+{
+	asm volatile (
+		"r2 = %[iter_limit_cb];"
+		"r3 = 0;"
+		"r4 = 0;"
+		"call %[bpf_loop];"
+		"exit;"
+		:
+		: __imm_ptr(iter_limit_cb),
+		  __imm(bpf_loop)
+		: __clobber_common
+	);
+}
+
 SEC("?raw_tp")
 __success
 int bpf_loop_iter_limit_ok(void *unused)