When `git blame` shows date field in a fixed width (as long as
blame_date_width characters), if time_str shorter than that, add spaces
for padding.  But there are two bugs in the following codes:

        memcpy(time_buf, time_str, time_len);
        memset(time_buf + time_len, ' ', blame_date_width - time_len);

1. The type of blame_date_width is size_t (unsigned int).  If time_len
   is greater than blame_ate_width, "blame_date_width - time_len" will
   never be a negative number, but a really big positive number, and
   will cause memory overwrite.

   This bug can be triggered if either l10n message for function
   show_date_relative() in date.c is longer then 30 charcters, then
   `git blame --date relative` may fail.

2. When show blame information with relative time, the UTF-8 characters
   in time_str will break the alignment of columns after the date field.
   This is because the time_buf padding with spaces should have a
   constant display width, not a fixed strlen size.  So we should call
   utf8_strwidth() instead of strlen() for calibration.

Signed-off-by: Jiang Xin <worldhello....@gmail.com>
 builtin/blame.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/builtin/blame.c b/builtin/blame.c
index 88cb799..0a0a858 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1556,22 +1556,31 @@ static void assign_blame(struct scoreboard *sb, int opt)
 static const char *format_time(unsigned long time, const char *tz_str,
                               int show_raw_time)
-       static char time_buf[128];
+       static struct strbuf time_buf = STRBUF_INIT;
+       strbuf_reset(&time_buf);
        if (show_raw_time) {
-               snprintf(time_buf, sizeof(time_buf), "%lu %s", time, tz_str);
+               strbuf_addf(&time_buf, "%lu %s", time, tz_str);
        else {
                const char *time_str;
+               size_t time_width;
                int time_len;
                int tz;
                tz = atoi(tz_str);
                time_str = show_date(time, tz, blame_date_mode);
                time_len = strlen(time_str);
-               memcpy(time_buf, time_str, time_len);
-               memset(time_buf + time_len, ' ', blame_date_width - time_len);
+               strbuf_add(&time_buf, time_str, time_len);
+               /*
+                * Add space paddings to time_buf to display a fixed width
+                * string, and use time_width for display width calibration.
+                */
+               for (time_width = utf8_strwidth(time_str);
+                    time_width < blame_date_width;
+                    time_width++)
+                       strbuf_addch(&time_buf, ' ');
-       return time_buf;
+       return time_buf.buf;

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