diff --git a/Makefile b/Makefile
index 5f3987fe3b..36655d5a16 100644
--- a/Makefile
+++ b/Makefile
@@ -359,6 +359,8 @@ all::
 # compiler is detected to support it.
 #
 # Define HAVE_BSD_SYSCTL if your platform has a BSD-compatible sysctl function.
+#
+# Define HAVE_GETDELIM if your system has the getdelim() function.
 
 GIT-VERSION-FILE: FORCE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -1437,6 +1439,10 @@ ifdef HAVE_BSD_SYSCTL
 	BASIC_CFLAGS += -DHAVE_BSD_SYSCTL
 endif
 
+ifdef HAVE_GETDELIM
+	BASIC_CFLAGS += -DHAVE_GETDELIM
+endif
+
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK = NoThanks
 endif
diff --git a/config.c b/config.c
index c4424c0138..6d0098fc80 100644
--- a/config.c
+++ b/config.c
@@ -50,7 +50,7 @@ static struct config_set the_config_set;
 
 static int config_file_fgetc(struct config_source *conf)
 {
-	return fgetc(conf->u.file);
+	return getc_unlocked(conf->u.file);
 }
 
 static int config_file_ungetc(int c, struct config_source *conf)
@@ -1088,7 +1088,9 @@ int git_config_from_file(config_fn_t fn, const char *filename, void *data)
 
 	f = fopen(filename, "r");
 	if (f) {
+		flockfile(f);
 		ret = do_config_from_file(fn, filename, filename, f, data);
+		funlockfile(f);
 		fclose(f);
 	}
 	return ret;
diff --git a/config.mak.uname b/config.mak.uname
index f4e77cb9e5..d26665fa54 100644
--- a/config.mak.uname
+++ b/config.mak.uname
@@ -36,6 +36,7 @@ ifeq ($(uname_S),Linux)
 	HAVE_DEV_TTY = YesPlease
 	HAVE_CLOCK_GETTIME = YesPlease
 	HAVE_CLOCK_MONOTONIC = YesPlease
+	HAVE_GETDELIM = YesPlease
 endif
 ifeq ($(uname_S),GNU/kFreeBSD)
 	HAVE_ALLOCA_H = YesPlease
diff --git a/git-compat-util.h b/git-compat-util.h
index bc8fc8cf85..685a0a4063 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -883,4 +883,10 @@ struct tm *git_gmtime_r(const time_t *, struct tm *);
 # define SHELL_PATH "/bin/sh"
 #endif
 
+#ifndef _POSIX_THREAD_SAFE_FUNCTIONS
+#define flockfile(fh)
+#define funlockfile(fh)
+#define getc_unlocked(fh) getc(fh)
+#endif
+
 #endif
diff --git a/refs.c b/refs.c
index 0312f05257..81a455b807 100644
--- a/refs.c
+++ b/refs.c
@@ -344,8 +344,6 @@ static struct ref_entry *create_ref_entry(const char *refname,
 	if (check_name &&
 	    check_refname_format(refname, REFNAME_ALLOW_ONELEVEL))
 		die("Reference has invalid format: '%s'", refname);
-	if (!check_name && !refname_is_safe(refname))
-		die("Reference has invalid name: '%s'", refname);
 	len = strlen(refname) + 1;
 	ref = xmalloc(sizeof(struct ref_entry) + len);
 	hashcpy(ref->u.value.sha1, sha1);
@@ -1178,6 +1176,8 @@ static void read_packed_refs(FILE *f, struct ref_dir *dir)
 			int flag = REF_ISPACKED;
 
 			if (check_refname_format(refname, REFNAME_ALLOW_ONELEVEL)) {
+				if (!refname_is_safe(refname))
+					die("packed refname is dangerous: %s", refname);
 				hashclr(sha1);
 				flag |= REF_BAD_NAME | REF_ISBROKEN;
 			}
@@ -1323,6 +1323,8 @@ static void read_loose_refs(const char *dirname, struct ref_dir *dir)
 			}
 			if (check_refname_format(refname.buf,
 						 REFNAME_ALLOW_ONELEVEL)) {
+				if (!refname_is_safe(refname.buf))
+					die("loose refname is dangerous: %s", refname.buf);
 				hashclr(sha1);
 				flag |= REF_BAD_NAME | REF_ISBROKEN;
 			}
diff --git a/strbuf.c b/strbuf.c
index 88cafd4a70..0d4f4e54ec 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -435,6 +435,47 @@ int strbuf_getcwd(struct strbuf *sb)
 	return -1;
 }
 
+#ifdef HAVE_GETDELIM
+int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
+{
+	ssize_t r;
+
+	if (feof(fp))
+		return EOF;
+
+	strbuf_reset(sb);
+
+	/* Translate slopbuf to NULL, as we cannot call realloc on it */
+	if (!sb->alloc)
+		sb->buf = NULL;
+	r = getdelim(&sb->buf, &sb->alloc, term, fp);
+
+	if (r > 0) {
+		sb->len = r;
+		return 0;
+	}
+	assert(r == -1);
+
+	/*
+	 * Normally we would have called xrealloc, which will try to free
+	 * memory and recover. But we have no way to tell getdelim() to do so.
+	 * Worse, we cannot try to recover ENOMEM ourselves, because we have
+	 * no idea how many bytes were read by getdelim.
+	 *
+	 * Dying here is reasonable. It mirrors what xrealloc would do on
+	 * catastrophic memory failure. We skip the opportunity to free pack
+	 * memory and retry, but that's unlikely to help for a malloc small
+	 * enough to hold a single line of input, anyway.
+	 */
+	if (errno == ENOMEM)
+		die("Out of memory, getdelim failed");
+
+	/* Restore slopbuf that we moved out of the way before */
+	if (!sb->buf)
+		strbuf_init(sb, 0);
+	return EOF;
+}
+#else
 int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
 {
 	int ch;
@@ -443,18 +484,22 @@ int strbuf_getwholeline(struct strbuf *sb, FILE *fp, int term)
 		return EOF;
 
 	strbuf_reset(sb);
-	while ((ch = fgetc(fp)) != EOF) {
-		strbuf_grow(sb, 1);
+	flockfile(fp);
+	while ((ch = getc_unlocked(fp)) != EOF) {
+		if (!strbuf_avail(sb))
+			strbuf_grow(sb, 1);
 		sb->buf[sb->len++] = ch;
 		if (ch == term)
 			break;
 	}
+	funlockfile(fp);
 	if (ch == EOF && sb->len == 0)
 		return EOF;
 
 	sb->buf[sb->len] = '\0';
 	return 0;
 }
+#endif
 
 int strbuf_getline(struct strbuf *sb, FILE *fp, int term)
 {
diff --git a/strbuf.h b/strbuf.h
index 1883494ca3..01c5c6371b 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -205,7 +205,8 @@ extern int strbuf_cmp(const struct strbuf *, const struct strbuf *);
  */
 static inline void strbuf_addch(struct strbuf *sb, int c)
 {
-	strbuf_grow(sb, 1);
+	if (!strbuf_avail(sb))
+		strbuf_grow(sb, 1);
 	sb->buf[sb->len++] = c;
 	sb->buf[sb->len] = '\0';
 }
diff --git a/t/t1430-bad-ref-name.sh b/t/t1430-bad-ref-name.sh
index 468e85621a..16d0b8bd1a 100755
--- a/t/t1430-bad-ref-name.sh
+++ b/t/t1430-bad-ref-name.sh
@@ -68,6 +68,14 @@ test_expect_success 'branch -D cannot delete non-ref in .git dir' '
 	test_cmp expect .git/my-private-file
 '
 
+test_expect_success 'branch -D cannot delete ref in .git dir' '
+	git rev-parse HEAD >.git/my-private-file &&
+	git rev-parse HEAD >expect &&
+	git branch foo/legit &&
+	test_must_fail git branch -D foo////./././../../../my-private-file &&
+	test_cmp expect .git/my-private-file
+'
+
 test_expect_success 'branch -D cannot delete absolute path' '
 	git branch -f extra &&
 	test_must_fail git branch -D "$(pwd)/.git/refs/heads/extra" &&