Merge branch 'ms/worktree-add-atomic-mkdir'

"git worktree add" used to do a "find an available name with stat
and then mkdir", which is race-prone.  This has been fixed by using
mkdir and reacting to EEXIST in a loop.

* ms/worktree-add-atomic-mkdir:
worktree: fix worktree add race

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 6cc094a453806308442d054a7d1c073ecf18b87b..d2a7e2f3f18ba411d065a52ac868db612de5beaa 100644 (file)
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -268,10 +268,10 @@ static int add_worktree(const char *path, const char *refname,
        struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
        struct strbuf sb = STRBUF_INIT;
        const char *name;
-       struct stat st;
        struct child_process cp = CHILD_PROCESS_INIT;
        struct argv_array child_env = ARGV_ARRAY_INIT;
-       int counter = 0, len, ret;
+       unsigned int counter = 0;
+       int len, ret;
        struct strbuf symref = STRBUF_INIT;
        struct commit *commit = NULL;
        int is_branch = 0;
@@ -295,8 +295,12 @@ static int add_worktree(const char *path, const char *refname,
        if (safe_create_leading_directories_const(sb_repo.buf))
                die_errno(_("could not create leading directories of '%s'"),
                          sb_repo.buf);
-       while (!stat(sb_repo.buf, &st)) {
+
+       while (mkdir(sb_repo.buf, 0777)) {
                counter++;
+               if ((errno != EEXIST) || !counter /* overflow */)
+                       die_errno(_("could not create directory of '%s'"),
+                                 sb_repo.buf);
                strbuf_setlen(&sb_repo, len);
                strbuf_addf(&sb_repo, "%d", counter);
        }
@@ -306,8 +310,6 @@ static int add_worktree(const char *path, const char *refname,
        atexit(remove_junk);
        sigchain_push_common(remove_junk_on_signal);
 
-       if (mkdir(sb_repo.buf, 0777))
-               die_errno(_("could not create directory of '%s'"), sb_repo.buf);
        junk_git_dir = xstrdup(sb_repo.buf);
        is_junk = 1;