From 1b18907dde2de75c9762d425c862586e1f7c438a Mon Sep 17 00:00:00 2001 From: Daniel J Walsh Date: Tue, 16 Nov 2021 08:22:31 -0800 Subject: [PATCH] Add LfileLabel and LsetFileLabel SELinux C library has two functions for dealing with file labels, one which follows symlinks and one that does not. Golang bindings should work the same way. The lack of this function is resulting in https://github.com/containers/buildah/pull/3630 which has to hack around the problem. Signed-off-by: Daniel J Walsh --- go-selinux/selinux.go | 18 +++++++++++++-- go-selinux/selinux_linux.go | 45 ++++++++++++++++++++++++++++++++++--- go-selinux/selinux_stub.go | 8 +++++++ go-selinux/xattrs_linux.go | 33 +++++++++++++++++++++++++++ 4 files changed, 99 insertions(+), 5 deletions(-) diff --git a/go-selinux/selinux.go b/go-selinux/selinux.go index cad4675..5a59d15 100644 --- a/go-selinux/selinux.go +++ b/go-selinux/selinux.go @@ -61,16 +61,30 @@ func ClassIndex(class string) (int, error) { return classIndex(class) } -// SetFileLabel sets the SELinux label for this path or returns an error. +// SetFileLabel sets the SELinux label for this path, following symlinks, +// or returns an error. func SetFileLabel(fpath string, label string) error { return setFileLabel(fpath, label) } -// FileLabel returns the SELinux label for this path or returns an error. +// LsetFileLabel sets the SELinux label for this path, not following symlinks, +// or returns an error. +func LsetFileLabel(fpath string, label string) error { + return lSetFileLabel(fpath, label) +} + +// FileLabel returns the SELinux label for this path, following symlinks, +// or returns an error. func FileLabel(fpath string) (string, error) { return fileLabel(fpath) } +// LfileLabel returns the SELinux label for this path, not following symlinks, +// or returns an error. +func LfileLabel(fpath string) (string, error) { + return lFileLabel(fpath) +} + // SetFSCreateLabel tells the kernel what label to use for all file system objects // created by this task. // Set the label to an empty string to return to the default label. Calls to SetFSCreateLabel diff --git a/go-selinux/selinux_linux.go b/go-selinux/selinux_linux.go index b045843..ee602ab 100644 --- a/go-selinux/selinux_linux.go +++ b/go-selinux/selinux_linux.go @@ -316,8 +316,9 @@ func classIndex(class string) (int, error) { return index, nil } -// setFileLabel sets the SELinux label for this path or returns an error. -func setFileLabel(fpath string, label string) error { +// lSetFileLabel sets the SELinux label for this path, not following symlinks, +// or returns an error. +func lSetFileLabel(fpath string, label string) error { if fpath == "" { return ErrEmptyPath } @@ -334,12 +335,50 @@ func setFileLabel(fpath string, label string) error { return nil } -// fileLabel returns the SELinux label for this path or returns an error. +// setFileLabel sets the SELinux label for this path, following symlinks, +// or returns an error. +func setFileLabel(fpath string, label string) error { + if fpath == "" { + return ErrEmptyPath + } + for { + err := unix.Setxattr(fpath, xattrNameSelinux, []byte(label), 0) + if err == nil { + break + } + if err != unix.EINTR { //nolint:errorlint // unix errors are bare + return &os.PathError{Op: "setxattr", Path: fpath, Err: err} + } + } + + return nil +} + +// fileLabel returns the SELinux label for this path, following symlinks, +// or returns an error. func fileLabel(fpath string) (string, error) { if fpath == "" { return "", ErrEmptyPath } + label, err := getxattr(fpath, xattrNameSelinux) + if err != nil { + return "", &os.PathError{Op: "getxattr", Path: fpath, Err: err} + } + // Trim the NUL byte at the end of the byte buffer, if present. + if len(label) > 0 && label[len(label)-1] == '\x00' { + label = label[:len(label)-1] + } + return string(label), nil +} + +// lFileLabel returns the SELinux label for this path, not following symlinks, +// or returns an error. +func lFileLabel(fpath string) (string, error) { + if fpath == "" { + return "", ErrEmptyPath + } + label, err := lgetxattr(fpath, xattrNameSelinux) if err != nil { return "", &os.PathError{Op: "lgetxattr", Path: fpath, Err: err} diff --git a/go-selinux/selinux_stub.go b/go-selinux/selinux_stub.go index 4265775..78743b0 100644 --- a/go-selinux/selinux_stub.go +++ b/go-selinux/selinux_stub.go @@ -17,10 +17,18 @@ func setFileLabel(fpath string, label string) error { return nil } +func lSetFileLabel(fpath string, label string) error { + return nil +} + func fileLabel(fpath string) (string, error) { return "", nil } +func lFileLabel(fpath string) (string, error) { + return "", nil +} + func setFSCreateLabel(label string) error { return nil } diff --git a/go-selinux/xattrs_linux.go b/go-selinux/xattrs_linux.go index c6b0a7f..9e473ca 100644 --- a/go-selinux/xattrs_linux.go +++ b/go-selinux/xattrs_linux.go @@ -36,3 +36,36 @@ func doLgetxattr(path, attr string, dest []byte) (int, error) { } } } + +// getxattr returns a []byte slice containing the value of +// an extended attribute attr set for path. +func getxattr(path, attr string) ([]byte, error) { + // Start with a 128 length byte array + dest := make([]byte, 128) + sz, errno := dogetxattr(path, attr, dest) + for errno == unix.ERANGE { //nolint:errorlint // unix errors are bare + // Buffer too small, use zero-sized buffer to get the actual size + sz, errno = dogetxattr(path, attr, []byte{}) + if errno != nil { + return nil, errno + } + + dest = make([]byte, sz) + sz, errno = dogetxattr(path, attr, dest) + } + if errno != nil { + return nil, errno + } + + return dest[:sz], nil +} + +// dogetxattr is a wrapper that retries on EINTR +func dogetxattr(path, attr string, dest []byte) (int, error) { + for { + sz, err := unix.Getxattr(path, attr, dest) + if err != unix.EINTR { //nolint:errorlint // unix errors are bare + return sz, err + } + } +}