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authorSebastian Lackner2019-01-05 15:44:32 +0100
committerJakob Unterwurzacher2019-01-05 16:12:16 +0100
commit7e05e809b7579ad0473fff6ce466c19d417d4e93 (patch)
treef4ba0f8b29c2a1ac7595b544a335db3aa32d75ed /internal
parentad15ad99856f90f3a72be4bd22ce44338645c963 (diff)
main: Run 'ensure fds' code early during the program startup.
The files are apparently processed in alphabetic order, so cli_args.go is processed before main.go. In order to run before the go-fuse imports, put the 'ensure fds' code in a separate package. Debug messages are omitted to avoid additional imports (that might contain other code messing up our file descriptors).
Diffstat (limited to 'internal')
-rw-r--r--internal/ensurefds012/ensurefds012.go52
-rw-r--r--internal/fusefrontend/dircache.go4
2 files changed, 56 insertions, 0 deletions
diff --git a/internal/ensurefds012/ensurefds012.go b/internal/ensurefds012/ensurefds012.go
new file mode 100644
index 0000000..7872eb2
--- /dev/null
+++ b/internal/ensurefds012/ensurefds012.go
@@ -0,0 +1,52 @@
+package ensurefds012
+
+// Package ensurefds012 ensures that file descriptors 0,1,2 are open. It opens
+// multiple copies of /dev/null as required.
+// The Go stdlib as well as the gocryptfs code rely on the fact that
+// fds 0,1,2 are always open.
+//
+// Use like this:
+//
+// import _ "github.com/rfjakob/gocryptfs/internal/ensurefds012"
+//
+// The import line MUST be in the alphabitcally first source code file of
+// package main!
+//
+// You can test if it works as expected by inserting a long sleep into main,
+// startings gocryptfs with all fds closed like this,
+//
+// $ ./gocryptfs 0<&- 1>&- 2>&-
+//
+// and then checking the open fds. It should look like this:
+//
+// $ ls -l /proc/$(pgrep gocryptfs)/fd
+// total 0
+// lrwx------. 1 jakob jakob 64 Jan 5 15:54 0 -> /dev/null
+// lrwx------. 1 jakob jakob 64 Jan 5 15:54 1 -> /dev/null
+// lrwx------. 1 jakob jakob 64 Jan 5 15:54 2 -> /dev/null
+// l-wx------. 1 jakob jakob 64 Jan 5 15:54 3 -> /dev/null
+// lrwx------. 1 jakob jakob 64 Jan 5 15:54 4 -> 'anon_inode:[eventpoll]'
+//
+// See https://github.com/rfjakob/gocryptfs/issues/320 for details.
+
+import (
+ "os"
+ "syscall"
+
+ "github.com/rfjakob/gocryptfs/internal/exitcodes"
+)
+
+func init() {
+ fd, err := syscall.Open("/dev/null", syscall.O_RDWR, 0)
+ if err != nil {
+ os.Exit(exitcodes.DevNull)
+ }
+ for fd <= 2 {
+ fd, err = syscall.Dup(fd)
+ if err != nil {
+ os.Exit(exitcodes.DevNull)
+ }
+ }
+ // Close excess fd (usually fd 3)
+ syscall.Close(fd)
+}
diff --git a/internal/fusefrontend/dircache.go b/internal/fusefrontend/dircache.go
index 6d0d570..68fd99c 100644
--- a/internal/fusefrontend/dircache.go
+++ b/internal/fusefrontend/dircache.go
@@ -35,6 +35,8 @@ type dirCacheEntryStruct struct {
func (e *dirCacheEntryStruct) Clear() {
// An earlier clear may have already closed the fd, or the cache
// has never been filled (fd is 0 in that case).
+ // Note: package ensurefds012, imported from main, guarantees that dirCache
+ // can never get fds 0,1,2.
if e.fd > 0 {
err := syscall.Close(e.fd)
if err != nil {
@@ -72,6 +74,8 @@ func (d *dirCacheStruct) Clear() {
// Store the entry in the cache. The passed "fd" will be Dup()ed, and the caller
// can close their copy at will.
func (d *dirCacheStruct) Store(dirRelPath string, fd int, iv []byte) {
+ // Note: package ensurefds012, imported from main, guarantees that dirCache
+ // can never get fds 0,1,2.
if fd <= 0 || len(iv) != nametransform.DirIVLen {
log.Panicf("Store sanity check failed: fd=%d len=%d", fd, len(iv))
}