fusefronted: fake fstat for deleted fifos

git test suite t9300-fast-import.sh test 245 does the equivalent of this:

	mkfifo fifo
	exec 8<>fifo
	rm fifo
	cat /dev/null >&8

This used to fail with

	cat: standard output: No such file or directory

because cat tries to fstat stdout.

The open() on the fifo does not reach the filesystem, so we don't
have an fd open for the delted file, hence no way to access it.

Fake fstat success as good as we can to make cat happy.

Fixes https://github.com/rfjakob/gocryptfs/issues/929

1 files changed, 26 insertions, 2 deletions

diff --git a/internal/fusefrontend/node.go b/internal/fusefrontend/node.go
index 91c947e..95be48d 100644
--- a/internal/fusefrontend/node.go
+++ b/internal/fusefrontend/node.go
@@ -75,26 +75,50 @@ func (n *Node) Getattr(ctx context.Context, f fs.FileHandle, out *fuse.AttrOut)
 			return fga.Getattr(ctx, out)
 		}
 	}
+	rn := n.rootNode()
+	var st *syscall.Stat_t
+	var err error
 
 	dirfd, cName, errno := n.prepareAtSyscallMyself()
+	// Hack for deleted fifos. As OPEN on a fifo does not reach
+	// the filesystem, we have no fd to access it. To make "cat" and git's
+	// t9300-fast-import.sh happy, we fake it as best as we can.
+	// https://github.com/rfjakob/gocryptfs/issues/929
+	if errno == syscall.ENOENT && n.StableAttr().Mode == syscall.S_IFIFO {
+		out.Mode = syscall.S_IFIFO
+		out.Ino = n.StableAttr().Ino
+		// cat looks at this to determine the optimal io size. Seems to be always 4096 for fifos.
+		out.Blksize = 4096
+		// We don't know what the owner was. Set it to nobody which seems safer
+		// than leaving it at 0 (root).
+		out.Owner.Gid = 65534
+		out.Owner.Uid = 65534
+		// All the other fields stay 0. This is what cat sees (strace -v log):
+		//
+		// fstat(1, {st_dev=makedev(0, 0x4d), st_ino=3838227, st_mode=S_IFIFO|000, st_nlink=0,
+		// st_uid=65534, st_gid=65534, st_blksize=4096, st_blocks=0, st_size=0, st_atime=0,
+		// st_atime_nsec=0, st_mtime=0, st_mtime_nsec=0, st_ctime=0, st_ctime_nsec=0}) = 0
+		goto out
+	}
 	if errno != 0 {
 		return
 	}
+
 	defer syscall.Close(dirfd)
 
-	st, err := syscallcompat.Fstatat2(dirfd, cName, unix.AT_SYMLINK_NOFOLLOW)
+	st, err = syscallcompat.Fstatat2(dirfd, cName, unix.AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		return fs.ToErrno(err)
 	}
 
 	// Fix inode number
-	rn := n.rootNode()
 	rn.inoMap.TranslateStat(st)
 	out.Attr.FromStat(st)
 
 	// Translate ciphertext size in `out.Attr.Size` to plaintext size
 	n.translateSize(dirfd, cName, &out.Attr)
 
+out:
 	if rn.args.ForceOwner != nil {
 		out.Owner = *rn.args.ForceOwner
 	}