bpftool: Remove BPF_OBJ_NAME_LEN restriction when looking up bpf program by name

bpftool was limiting the length of names to BPF_OBJ_NAME_LEN in prog_parse
fds.

Since commit b662000aff84 ("bpftool: Adding support for BTF program names")
we can get the full program name from BTF.

This patch removes the restriction of name length when running `bpftool
prog show name ${name}`.

Test:
Tested against some internal program names that were longer than
`BPF_OBJ_NAME_LEN`, here a redacted example of what was ran to test.

# previous behaviour
$ sudo bpftool prog show name some_long_program_name
Error: can't parse name
# with the patch
$ sudo ./bpftool prog show name some_long_program_name
123456789: tracing name some_long_program_name tag taghexa gpl ....
...
...
...
# too long
sudo ./bpftool prog show name $(python3 -c 'print("A"*128)')
Error: can't parse name
# not too long but no match
$ sudo ./bpftool prog show name $(python3 -c 'print("A"*127)')

Signed-off-by: Manu Bretelle <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Tested-by: Jiri Olsa <[e-mail]>
Reviewed-by: Quentin Monnet <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/bpf/bpftool/common.c

···
 
 static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
 {
+	char prog_name[MAX_PROG_FULL_NAME];
 	unsigned int id = 0;
 	int fd, nb_fds = 0;
 	void *tmp;
···
 			goto err_close_fd;
 		}
 
-		if ((tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) ||
-		    (!tag && strncmp(nametag, info.name, BPF_OBJ_NAME_LEN))) {
+		if (tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) {
 			close(fd);
 			continue;
+		}
+
+		if (!tag) {
+			get_prog_full_name(&info, fd, prog_name,
+					   sizeof(prog_name));
+			if (strncmp(nametag, prog_name, sizeof(prog_name))) {
+				close(fd);
+				continue;
+			}
 		}
 
 		if (nb_fds > 0) {
···
 		NEXT_ARGP();
 
 		name = **argv;
-		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
+		if (strlen(name) > MAX_PROG_FULL_NAME - 1) {
 			p_err("can't parse name");
 			return -1;
 		}