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fusefrontend: make SetXAttr() symlink-safe on Linux

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Uses the /proc/self/fd trick.
This commit is contained in:
Jakob Unterwurzacher 2018-11-11 17:57:24 +01:00
parent 2286372603
commit 810d2a8b47
3 changed files with 37 additions and 17 deletions
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25
internal/fusefrontend/xattr.go
View File

@ -26,8 +26,8 @@ var xattrStorePrefix = "user.gocryptfs."
// GetXAttr - FUSE call. Reads the value of extended attribute "attr".
//
// This function is symlink-safe on Linux.
// Darwin does not have fgetxattr(2) nor /proc. How to implement this on Darwin
// in a symlink-safe way?
// Darwin does not have fgetxattr(2) nor /proc/self/fd. How to implement this
// on Darwin in a symlink-safe way?
func (fs *FS) GetXAttr(relPath string, attr string, context *fuse.Context) ([]byte, fuse.Status) {
if fs.isFiltered(relPath) {
return nil, fuse.EPERM
@ -48,27 +48,22 @@ func (fs *FS) GetXAttr(relPath string, attr string, context *fuse.Context) ([]by
return data, fuse.OK
}
// SetXAttr - FUSE call.
// SetXAttr - FUSE call. Set extended attribute.
//
// TODO: Make symlink-safe. Currently blocked because the xattr package does
// not provide fsetxattr.
func (fs *FS) SetXAttr(path string, attr string, data []byte, flags int, context *fuse.Context) fuse.Status {
if fs.isFiltered(path) {
// This function is symlink-safe on Linux.
// Darwin does not have fsetxattr(2) nor /proc/self/fd. How to implement this
// on Darwin in a symlink-safe way?
func (fs *FS) SetXAttr(relPath string, attr string, data []byte, flags int, context *fuse.Context) fuse.Status {
if fs.isFiltered(relPath) {
return fuse.EPERM
}
if disallowedXAttrName(attr) {
return _EOPNOTSUPP
}
flags = filterXattrSetFlags(flags)
cPath, err := fs.getBackingPath(path)
if err != nil {
return fuse.ToStatus(err)
}
cAttr := fs.encryptXattrName(attr)
cData := fs.encryptXattrValue(data)
return unpackXattrErr(xattr.LSetWithFlags(cPath, cAttr, cData, flags))
return fs.setXattr(relPath, cAttr, cData, flags, context)
}
// RemoveXAttr - FUSE call.
@ -175,7 +170,7 @@ func (fs *FS) decryptXattrValue(cData []byte) (data []byte, err error) {
}
// unpackXattrErr unpacks an error value that we got from xattr.LGet/LSet/etc
// and converts it to a fuse status.
// and converts it to a fuse status. If err == nil, it returns fuse.OK.
func unpackXattrErr(err error) fuse.Status {
if err == nil {
return fuse.OK

9
internal/fusefrontend/xattr_darwin.go
View File

@ -30,3 +30,12 @@ func (fs *FS) getXattr(relPath string, cAttr string, context *fuse.Context) ([]b
}
return cData, fuse.OK
}
func (fs *FS) setXattr(relPath string, cAttr string, cData []byte, flags int, context *fuse.Context) fuse.Status {
cPath, err := fs.getBackingPath(relPath)
if err != nil {
return fuse.ToStatus(err)
}
err = xattr.LSetWithFlags(cPath, cAttr, cData, flags)
return unpackXattrErr(err)
}

20
internal/fusefrontend/xattr_linux.go
View File

@ -28,6 +28,7 @@ func filterXattrSetFlags(flags int) int {
return flags
}
// procFd returns the path to file descriptor "fd" in /proc/self/fd.
func procFd(fd int) string {
return fmt.Sprintf("/proc/self/fd/%d", fd)
}
@ -51,10 +52,10 @@ func (fs *FS) getFileFd(relPath string, context *fuse.Context) (*File, int, fuse
return file, file.intFd(), fuse.OK
}
// getXattr - read encrypted xattr name "cAttr" from the file at relative
// getXattr - read encrypted xattr name "cAttr" from relative
// plaintext path "relPath". Returns the encrypted xattr value.
//
// This function is symlink-safe.
// This function is symlink-safe by using /proc/self/fd.
func (fs *FS) getXattr(relPath string, cAttr string, context *fuse.Context) ([]byte, fuse.Status) {
file, fd, status := fs.getFileFd(relPath, context)
if !status.Ok() {
@ -68,3 +69,18 @@ func (fs *FS) getXattr(relPath string, cAttr string, context *fuse.Context) ([]b
}
return cData, fuse.OK
}
// setXattr - set encrypted xattr name "cAttr" to value "cData" on plaintext
// path "relPath".
//
// This function is symlink-safe by using /proc/self/fd.
func (fs *FS) setXattr(relPath string, cAttr string, cData []byte, flags int, context *fuse.Context) fuse.Status {
file, fd, status := fs.getFileFd(relPath, context)
if !status.Ok() {
return status
}
defer file.Release()
err := xattr.SetWithFlags(procFd(fd), cAttr, cData, flags)
return unpackXattrErr(err)
}