[PATCH] setup: don't die if realpath(3) fails on getcwd(3)

From: Kevin Locke <kevin@kevinlocke.name>
Date: May 19, 2022, 23:39 UTC
Message-ID: <80eeba2b2a58af2a5497f398beb5c03447c41f61.1653003552.git.kevin@kevinlocke.name>

Prior to Git 2.35.0, git could be run from an inaccessible working directory so long as the git repository specified by options and/or environment variables was accessible. For example:

    git init repo
    mkdir -p a/b
    cd a/b
    chmod u-x ..
    git -C "${PWD%/a/b}/repo" status

If this example seems a bit contrived, consider running with the repository owner as a substitute UID (e.g. with runuser(1) or sudo(8)) without ensuring the working directory is accessible by that user.

The code added by e6f8861bd4 to preserve the working directory attempts to normalize the path using strbuf_realpath(). If that fails, as in the case above, it is treated as a fatal error. To avoid this, we can continue after the error. At worst, git will fail to detect that the working directory is inside the worktree, resulting in the pre-2.35.0 behavior of not preserving the working directory.

Fixes: e6f8861bd4 ("setup: introduce startup_info->original_cwd")
Signed-off-by: Kevin Locke <kevin@kevinlocke.name>
---
 setup.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/setup.c b/setup.c
index a7b36f3ffb..fb68caaae0 100644
--- a/setup.c
+++ b/setup.c
@@ -458,11 +458,13 @@ static void setup_original_cwd(void)
 	 *     not startup_info->original_cwd.
 	 */
 
-	/* Normalize the directory */
-	strbuf_realpath(&tmp, tmp_original_cwd, 1);
-	free((char*)tmp_original_cwd);
+	/* Try to normalize the directory.  Fails if ancestor not readable. */
+	if (strbuf_realpath(&tmp, tmp_original_cwd, 0)) {
+		free((char*)tmp_original_cwd);
+		startup_info->original_cwd = strbuf_detach(&tmp, NULL);
+	} else
+		startup_info->original_cwd = tmp_original_cwd;
 	tmp_original_cwd = NULL;
-	startup_info->original_cwd = strbuf_detach(&tmp, NULL);
 
 	/*
 	 * Get our worktree; we only protect the current working directory

-- 
2.35.1