Merge branch 'dt/xgethostname-nul-termination'

gethostname(2) may not NUL terminate the buffer if hostname does
not fit; unfortunately there is no easy way to see if our buffer
was too small, but at least this will make sure we will not end up
using garbage past the end of the buffer.

* dt/xgethostname-nul-termination:
  xgethostname: handle long hostnames
  use HOST_NAME_MAX to size buffers for gethostname(2)

builtin/gc.c

@@ -232,7 +232,7 @@ static int need_to_gc(void)
 static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
 {
 	static struct lock_file lock;
-	char my_host[128];
+	char my_host[HOST_NAME_MAX + 1];
 	struct strbuf sb = STRBUF_INIT;
 	struct stat st;
 	uintmax_t pid;
@@ -244,15 +244,19 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
 		/* already locked */
 		return NULL;
 
-	if (gethostname(my_host, sizeof(my_host)))
+	if (xgethostname(my_host, sizeof(my_host)))
 		xsnprintf(my_host, sizeof(my_host), "unknown");
 
 	pidfile_path = git_pathdup("gc.pid");
 	fd = hold_lock_file_for_update(&lock, pidfile_path,
 				       LOCK_DIE_ON_ERROR);
 	if (!force) {
-		static char locking_host[128];
+		static char locking_host[HOST_NAME_MAX + 1];
+		static char *scan_fmt;
 		int should_exit;
+
+		if (!scan_fmt)
+			scan_fmt = xstrfmt("%s %%%dc", "%"SCNuMAX, HOST_NAME_MAX);
 		fp = fopen(pidfile_path, "r");
 		memset(locking_host, 0, sizeof(locking_host));
 		should_exit =
@@ -268,7 +272,7 @@ static const char *lock_repo_for_gc(int force, pid_t* ret_pid)
 			 * running.
 			 */
 			time(NULL) - st.st_mtime <= 12 * 3600 &&
-			fscanf(fp, "%"SCNuMAX" %127c", &pid, locking_host) == 2 &&
+			fscanf(fp, scan_fmt, &pid, locking_host) == 2 &&
 			/* be gentle to concurrent "gc" on remote hosts */
 			(strcmp(locking_host, my_host) || !kill(pid, 0) || errno == EPERM);
 		if (fp != NULL)

builtin/receive-pack.c

@@ -1697,12 +1697,12 @@ static const char *unpack(int err_fd, struct shallow_info *si)
 		if (status)
 			return "unpack-objects abnormal exit";
 	} else {
-		char hostname[256];
+		char hostname[HOST_NAME_MAX + 1];
 
 		argv_array_pushl(&child.args, "index-pack", "--stdin", NULL);
 		push_header_arg(&child.args, &hdr);
 
-		if (gethostname(hostname, sizeof(hostname)))
+		if (xgethostname(hostname, sizeof(hostname)))
 			xsnprintf(hostname, sizeof(hostname), "localhost");
 		argv_array_pushf(&child.args,
 				 "--keep=receive-pack %"PRIuMAX" on %s",

daemon.c

@@ -4,10 +4,6 @@
 #include "strbuf.h"
 #include "string-list.h"
 
-#ifndef HOST_NAME_MAX
-#define HOST_NAME_MAX 256
-#endif
-
 #ifdef NO_INITGROUPS
 #define initgroups(x, y) (0) /* nothing */
 #endif

fetch-pack.c

@@ -804,8 +804,8 @@ static int get_pack(struct fetch_pack_args *args,
 		if (args->use_thin_pack)
 			argv_array_push(&cmd.args, "--fix-thin");
 		if (args->lock_pack || unpack_limit) {
-			char hostname[256];
-			if (gethostname(hostname, sizeof(hostname)))
+			char hostname[HOST_NAME_MAX + 1];
+			if (xgethostname(hostname, sizeof(hostname)))
 				xsnprintf(hostname, sizeof(hostname), "localhost");
 			argv_array_pushf(&cmd.args,
 					"--keep=fetch-pack %"PRIuMAX " on %s",

git-compat-util.h

@@ -884,6 +884,12 @@ static inline size_t xsize_t(off_t len)
 __attribute__((format (printf, 3, 4)))
 extern int xsnprintf(char *dst, size_t max, const char *fmt, ...);
 
+#ifndef HOST_NAME_MAX
+#define HOST_NAME_MAX 256
+#endif
+
+extern int xgethostname(char *buf, size_t len);
+
 /* in ctype.c, for kwset users */
 extern const unsigned char tolower_trans_tbl[256];
 

ident.c

@@ -120,9 +120,9 @@ static int canonical_name(const char *host, struct strbuf *out)
 
 static void add_domainname(struct strbuf *out, int *is_bogus)
 {
-	char buf[1024];
+	char buf[HOST_NAME_MAX + 1];
 
-	if (gethostname(buf, sizeof(buf))) {
+	if (xgethostname(buf, sizeof(buf))) {
 		warning_errno("cannot get host name");
 		strbuf_addstr(out, "(none)");
 		*is_bogus = 1;

wrapper.c

@@ -655,3 +655,16 @@ void sleep_millisec(int millisec)
 {
 	poll(NULL, 0, millisec);
 }
+
+int xgethostname(char *buf, size_t len)
+{
+	/*
+	 * If the full hostname doesn't fit in buf, POSIX does not
+	 * specify whether the buffer will be null-terminated, so to
+	 * be safe, do it ourselves.
+	 */
+	int ret = gethostname(buf, len);
+	if (!ret)
+		buf[len - 1] = 0;
+	return ret;
+}