bpf: Fix a verifier verbose message

Long ago a map file descriptor in a pseudo ldimm64 instruction could
only be present as an immediate value insn[0].imm, and thus this value
was used in a verbose verifier message printed when the file descriptor
wasn't valid. Since addition of BPF_PSEUDO_MAP_IDX_VALUE/BPF_PSEUDO_MAP_IDX
the insn[0].imm field can also contain an index pointing to the file
descriptor in the attr.fd_array array. However, if the file descriptor
is invalid, the verifier still prints the verbose message containing
value of insn[0].imm. Patch the verifier message to always print the
actual file descriptor value.

Fixes: 387544bf ("bpf: Introduce fd_idx")
Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240412141100.3562942-1-aspsk@isovalent.com

kernel/bpf/verifier.c

@@ -18289,8 +18289,7 @@ static int resolve_pseudo_ldimm64(struct bpf_verifier_env *env)
 			f = fdget(fd);
 			map = __bpf_map_get(f);
 			if (IS_ERR(map)) {
-				verbose(env, "fd %d is not pointing to valid bpf_map\n",
-					insn[0].imm);
+				verbose(env, "fd %d is not pointing to valid bpf_map\n", fd);
 				return PTR_ERR(map);
 			}