bpftool: ensure task comm is always NUL-terminated

Let's explicitly ensure the destination string is NUL-terminated. This
way, it won't be affected by changes to the source string.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Yafang Shao <[e-mail]>
Reviewed-by: Quentin Monnet <[e-mail]>
Cc: Alejandro Colomar <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Andy Shevchenko <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Eric Biederman <[e-mail]>
Cc: Eric Paris <[e-mail]>
Cc: James Morris <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Justin Stitt <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Maarten Lankhorst <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Matus Jokay <[e-mail]>
Cc: Maxime Ripard <[e-mail]>
Cc: Ondrej Mosnacek <[e-mail]>
Cc: Paul Moore <[e-mail]>
Cc: "Serge E. Hallyn" <[e-mail]>
Cc: Simon Horman <[e-mail]>
Cc: Stephen Smalley <[e-mail]>
Cc: Steven Rostedt (Google) <[e-mail]>
Cc: Tetsuo Handa <[e-mail]>
Cc: Thomas Zimmermann <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

tools/bpf/bpftool/pids.c

···
 		ref = &refs->refs[refs->ref_cnt];
 		ref->pid = e->pid;
 		memcpy(ref->comm, e->comm, sizeof(ref->comm));
+		ref->comm[sizeof(ref->comm) - 1] = '\0';
 		refs->ref_cnt++;
 
 		return;
···
 	ref = &refs->refs[0];
 	ref->pid = e->pid;
 	memcpy(ref->comm, e->comm, sizeof(ref->comm));
+	ref->comm[sizeof(ref->comm) - 1] = '\0';
 	refs->ref_cnt = 1;
 	refs->has_bpf_cookie = e->has_bpf_cookie;
 	refs->bpf_cookie = e->bpf_cookie;