add/remove-shell: use O_TRUNC instead of O_EXCL

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/loginutils/add-remove-shell.c b/loginutils/add-remove-shell.c
index 986fe57c5..757e50503 100644
--- a/loginutils/add-remove-shell.c
+++ b/loginutils/add-remove-shell.c
@@ -63,11 +63,19 @@ int add_remove_shell_main(int argc UNUSED_PARAM, char **argv)
         orig_fp = fopen_for_read(orig_fn);
 
         new_fn = xasprintf("%s.tmp", orig_fn);
-        xmove_fd(xopen(new_fn, O_WRONLY | O_CREAT | O_EXCL), STDOUT_FILENO);
+        /*
+         * O_TRUNC or O_EXCL? At the first glance, O_EXCL looks better,
+         * since it prevents races. But: (1) it requires a retry loop,
+         * (2) if /etc/shells.tmp is *stale*, then retry loop
+         * with O_EXCL will never succeed - it should have a timeout,
+         * after which it should revert to O_TRUNC.
+         * For now, I settle for O_TRUNC instead.
+         */
+        xmove_fd(xopen(new_fn, O_WRONLY | O_CREAT | O_TRUNC), STDOUT_FILENO);
 
         /* TODO:
         struct stat sb;
-        fstat(fileno(orig_fp), &sb);
+        xfstat(fileno(orig_fp), &sb);
         xfchown(STDOUT_FILENO, sb.st_uid, sb.st_gid);
         xfchmod(STDOUT_FILENO, sb.st_mode);
         */