libfuse-sane: ship

pkgs/additional/libfuse-sane/default.nix

@@ -0,0 +1,31 @@
+{
+  fuse3
+}:
+let
+  patched = fuse3.overrideAttrs (upstream: {
+    outputs = upstream.outputs ++ [ "sane" ];
+    defaultOutput = "sane";
+    patches = (upstream.patches or []) ++ [
+      ./pass_fuse_fd.patch
+    ];
+    postFixup = (upstream.postFixup or "") + ''
+      ln -s $out/bin/mount.fuse3 $out/bin/mount.fuse3.sane
+      moveToOutput bin/mount.fuse3.sane "$sane"
+    '';
+    meta = (upstream.meta or {}) // {
+      mainProgram = "mount.fuse3.sane";
+      description = ''
+        provides `mount.fuse3.sane`, which behaves identically to `mount.fuse3` except
+        it supports an additional mount flag, `-o pass_fuse_fd`.
+
+        when mounting with `-o pass_fuse_fd`, `mount.fuse3.sane` opens the `/dev/fuse` device (which requires CAP_SYS_ADMIN),
+        and then `exec`s the userspace implementation, which inherits this file descriptor.
+        `mount.fuse3.sane` invokes the userspace implementation with the device argument set to something like `/dev/fd/3`, indicating which fd holds the fuse device.
+
+        the aim of this flag is to provide a clear handoff point at which the filesystem may drop CAP_SYS_ADMIN.
+        in this regard, it's much like `-o drop_privileges`, only it leaves the responsibility for that to the fs impl,
+        in case the fs needs to preserve _other_ privileges besides CAP_SYS_ADMIN.
+      '';
+    };
+  });
+in patched.sane

pkgs/additional/libfuse-sane/pass_fuse_fd.patch

@@ -0,0 +1,15 @@
+diff --git a/util/mount.fuse.c b/util/mount.fuse.c
+index b98fb2a..f46c4f7 100644
+--- a/util/mount.fuse.c
++++ b/util/mount.fuse.c
+@@ -327,6 +327,10 @@ int main(int argc, char *argv[])
+ 				if (strncmp(opt, "setuid=", 7) == 0) {
+ 					setuid_name = xstrdup(opt + 7);
+ 					ignore = 1;
++				} else if (strcmp(opt,
++						  "pass_fuse_fd") == 0) {
++					pass_fuse_fd = 1;
++					ignore = 1;
+ 				} else if (strcmp(opt,
+ 						  "drop_privileges") == 0) {
+ 					pass_fuse_fd = 1;

pkgs/default.nix

@@ -53,6 +53,7 @@ let
     lemmy-lemonade = callPackage ./additional/lemonade { };  # XXX: nixpkgs already has a `lemonade` pkg
     lgtrombetta-compass = callPackage ./additional/lgtrombetta-compass { };
     libdng = callPackage ./additional/libdng { };
+    libfuse-sane = callPackage ./additional/libfuse-sane { };
     libmegapixels = callPackage ./additional/libmegapixels { };
     lightdm-mobile-greeter = callPackage ./additional/lightdm-mobile-greeter { };
     linux-exynos5-mainline = callPackage ./additional/linux-exynos5-mainline { };