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[3/3] mingw: be more informative when ownership check fails on FAT32

Message ID dae03f1b20430ff93c826b126057961a9030f2bf.1657700238.git.gitgitgadget@gmail.com (mailing list archive)
State Superseded
Headers show
Series Some improvements to safe.directory on Windows | expand

Commit Message

Johannes Schindelin July 13, 2022, 8:17 a.m. UTC 
From: Johannes Schindelin <johannes.schindelin@gmx.de>

The FAT file system has no concept of ACLs. Therefore, it cannot store
any ownership information anyway, and the `GetNamedSecurityInfoW()` call
pretends that everything is owned "by the world".

Let's special-case that scenario and tell the user what's going on, at
least when they set `GIT_TEST_DEBUG_UNSAFE_DIRECTORIES`.

This addresses https://github.com/git-for-windows/git/issues/3886

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 compat/mingw.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)
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Patch

diff --git a/compat/mingw.c b/compat/mingw.c
index e0e020ee574..4144d6247bd 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -2630,6 +2630,21 @@  static PSID get_current_user_sid(void)
 	return result;
 }
 
+static int acls_supported(const char *path)
+{
+	size_t offset = offset_1st_component(path);
+	WCHAR wroot[MAX_PATH];
+	DWORD file_system_flags;
+
+	if (offset &&
+	    xutftowcsn(wroot, path, MAX_PATH, offset) > 0 &&
+	    GetVolumeInformationW(wroot, NULL, 0, NULL, NULL,
+				  &file_system_flags, NULL, 0))
+		return !!(file_system_flags & FILE_PERSISTENT_ACLS);
+
+	return 0;
+}
+
 int is_path_owned_by_current_sid(const char *path)
 {
 	WCHAR wpath[MAX_PATH];
@@ -2687,7 +2702,14 @@  int is_path_owned_by_current_sid(const char *path)
 			 * okay, too.
 			 */
 			result = 1;
-		else if (git_env_bool("GIT_TEST_DEBUG_UNSAFE_DIRECTORIES", 0)) {
+		else if (IsWellKnownSid(sid, WinWorldSid) &&
+			 git_env_bool("GIT_TEST_DEBUG_UNSAFE_DIRECTORIES", 0) &&
+			 !acls_supported(path)) {
+			/*
+			 * On FAT32 volumes, ownership is not actually recorded.
+			 */
+			warning("'%s' is on a file system that does not record ownership", path);
+		} else if (git_env_bool("GIT_TEST_DEBUG_UNSAFE_DIRECTORIES", 0)) {
 			LPSTR str1, str2, to_free1 = NULL, to_free2 = NULL;
 
 			if (ConvertSidToStringSidA(sid, &str1))