[PATCH] show-branch: fix crash with long ref name

[Christian Couder <christian.couder@gmail.com>]

This is a minimum fix for a crash with a long ref name.

Note that if the refname is too long (for example if you
use 100 instead of 50 in the test script) you could get
an error like:

fatal: cannot lock ref 'refs/heads/1_2_3_4_ ... _98_99_100_':
Unable to create '... /.git/refs/heads/1_2_3_4_ ... _98_99_100_.lock':
File name too long

when creating the ref instead of a crash when using
show-branch and that would be ok.

So a simpler fix could have been just something like:

-       char head[128];
+       char head[1024];

But if the filesystem ever allows filenames longer than 1024
characters then the crash could appear again.

Reported by: Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 builtin/show-branch.c          | 14 +++++++-------
 t/t3204-show-branch-refname.sh | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+), 7 deletions(-)
 create mode 100755 t/t3204-show-branch-refname.sh

diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index 974f3403ab..3c0fe55eec 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -620,7 +620,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 	int all_heads = 0, all_remotes = 0;
 	int all_mask, all_revs;
 	enum rev_sort_order sort_order = REV_SORT_IN_GRAPH_ORDER;
-	char head[128];
+	char *head_cpy;
 	const char *head_p;
 	int head_len;
 	struct object_id head_oid;
@@ -791,11 +791,11 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 				    head_oid.hash, NULL);
 	if (head_p) {
 		head_len = strlen(head_p);
-		memcpy(head, head_p, head_len + 1);
+		head_cpy = xstrdup(head_p);
 	}
 	else {
 		head_len = 0;
-		head[0] = 0;
+		head_cpy = xstrdup("");
 	}
 
 	if (with_current_branch && head_p) {
@@ -804,15 +804,15 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			/* We are only interested in adding the branch
 			 * HEAD points at.
 			 */
-			if (rev_is_head(head,
+			if (rev_is_head(head_cpy,
 					head_len,
 					ref_name[i],
 					head_oid.hash, NULL))
 				has_head++;
 		}
 		if (!has_head) {
-			int offset = starts_with(head, "refs/heads/") ? 11 : 0;
-			append_one_rev(head + offset);
+			int offset = starts_with(head_cpy, "refs/heads/") ? 11 : 0;
+			append_one_rev(head_cpy + offset);
 		}
 	}
 
@@ -865,7 +865,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 	if (1 < num_rev || extra < 0) {
 		for (i = 0; i < num_rev; i++) {
 			int j;
-			int is_head = rev_is_head(head,
+			int is_head = rev_is_head(head_cpy,
 						  head_len,
 						  ref_name[i],
 						  head_oid.hash,
diff --git a/t/t3204-show-branch-refname.sh b/t/t3204-show-branch-refname.sh
new file mode 100755
index 0000000000..83b64e3032
--- /dev/null
+++ b/t/t3204-show-branch-refname.sh
@@ -0,0 +1,19 @@
+#!/bin/sh
+
+test_description='test show-branch with long refname'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+
+	test_commit first &&
+	long_refname=$(printf "%s_" $(seq 1 50)) &&
+	git checkout -b "$long_refname"
+'
+
+test_expect_success 'show-branch with long refname' '
+
+	git show-branch first
+'
+
+test_done
-- 
2.12.0.rc0