RE: Permission issue in Git in DrvFs-mounted network drives

[<rsbecker@nexbridge.com>]

On September 18, 2024 12:16 PM, Marcos Del Sol Vives wrote:
>Under WSL1 (Windows Subsystem for Linux), when using a network share
>mounted via DrvFs, Git fails to add any files to a new or an existing repository.
>
>The reason is that Git tries to open a temporary file as with RW permissions but
>mode 0444, which causes WSL1 (or Samba, unsure who's here to blame) to create
>first an file empty with the read-only DOS attribute set that prevents any writes,
>and then actually trying to opening it in write mode, which of course fails.
>
>Seems to be a pretty common issue that nobody has yet reported officially, judging
>by the amount of posts on Stackoverflow, impacting not only WSL but also CIFS
>under Linux (hence why sending to this mailing list and not the Windows-specific
>one):
>
> - https://superuser.com/questions/681196/debugging-git-repo-permissions-on-
>samba-share
> - https://superuser.com/questions/1450094/git-on-wsl-commands-fail-despite-
>permissions-seeming-fine
> - https://superuser.com/questions/1491499/use-git-on-a-shared-drive-within-
>wsl
>
>As a workaround, opening the file with permissions 0600 and then using a fchmod
>with the final desired mode works, which is a very small change that should cause
>no issues under neither real Linux nor WSL:
>
>--- git-2.39.5.orig/wrapper.c
>+++ git-2.39.5/wrapper.c
>@@ -484,9 +484,11 @@ int git_mkstemps_mode(char *pattern, int
> 			v /= num_letters;
> 		}
>
>-		fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, mode);
>-		if (fd >= 0)
>+		fd = open(pattern, O_CREAT | O_EXCL | O_RDWR, 0600);
>+		if (fd >= 0) {
>+			fchmod(fd, mode);
> 			return fd;
>+		}

I am not certain this is either necessary or important to platforms other than Windows.
The /tmp directory is often, and properly set with the sticky bit +t. This ensures that only
The creating user has access to the temp file regardless of create ownership or security.
I would prefer that this be put into a compat layer rather than made general change.

> 		/*
> 		 * Fatal error (EPERM, ENOSPC etc).
> 		 * It doesn't make sense to loop.
>
>The WSL team at Microsoft has been already informed as well:
>https://github.com/microsoft/WSL/issues/12051