label: rework label_fix() implementations (#8583)

This reworks the SELinux and SMACK label fixing calls in a number of
ways:

1. The two separate boolean arguments of these functions are converted
   into a flags type LabelFixFlags.

2. The operations are now implemented based on O_PATH. This should
   resolve TTOCTTOU races between determining the label for the file
   system object and applying it, as it it allows to pin the object
   while we are operating on it.

3. When changing a label fails we'll query the label previously set, and
   if matches what we want to set anyway we'll suppress the error.

Also, all calls to label_fix() are now (void)ified, when we ignore the
return values.

Fixes: #8566

diff --git a/src/basic/label.c b/src/basic/label.c
index 18c9a23..134dd8d 100644 (file)
--- a/src/basic/label.c
+++ b/src/basic/label.c
@@ -28,11 +28,11 @@
 #include "selinux-util.h"
 #include "smack-util.h"
 
-int label_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
+int label_fix(const char *path, LabelFixFlags flags) {
         int r, q;
 
-        r = mac_selinux_fix(path, ignore_enoent, ignore_erofs);
-        q = mac_smack_fix(path, ignore_enoent, ignore_erofs);
+        r = mac_selinux_fix(path, flags);
+        q = mac_smack_fix(path, flags);
 
         if (r < 0)
                 return r;
@@ -60,7 +60,7 @@ int symlink_label(const char *old_path, const char *new_path) {
         if (r < 0)
                 return r;
 
-        return mac_smack_fix(new_path, false, false);
+        return mac_smack_fix(new_path, 0);
 }
 
 int btrfs_subvol_make_label(const char *path) {
@@ -78,5 +78,5 @@ int btrfs_subvol_make_label(const char *path) {
         if (r < 0)
                 return r;
 
-        return mac_smack_fix(path, false, false);
+        return mac_smack_fix(path, 0);
 }

diff --git a/src/basic/label.h b/src/basic/label.h
index d73dace..269591c 100644 (file)
--- a/src/basic/label.h
+++ b/src/basic/label.h
@@ -23,7 +23,12 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
-int label_fix(const char *path, bool ignore_enoent, bool ignore_erofs);
+typedef enum LabelFixFlags {
+        LABEL_IGNORE_ENOENT = 1U << 0,
+        LABEL_IGNORE_EROFS  = 1U << 1,
+} LabelFixFlags;
+
+int label_fix(const char *path, LabelFixFlags flags);
 
 int mkdir_label(const char *path, mode_t mode);
 int symlink_label(const char *old_path, const char *new_path);

diff --git a/src/basic/mkdir-label.c b/src/basic/mkdir-label.c
index 2a44d27..9d4ef60 100644 (file)
--- a/src/basic/mkdir-label.c
+++ b/src/basic/mkdir-label.c
@@ -44,7 +44,7 @@ int mkdir_label(const char *path, mode_t mode) {
         if (r < 0)
                 return r;
 
-        return mac_smack_fix(path, false, false);
+        return mac_smack_fix(path, 0);
 }
 
 int mkdir_safe_label(const char *path, mode_t mode, uid_t uid, gid_t gid, MkdirFlags flags) {

diff --git a/src/basic/selinux-util.c b/src/basic/selinux-util.c
index 0c6e99b..c60057f 100644 (file)
--- a/src/basic/selinux-util.c
+++ b/src/basic/selinux-util.c
@@ -34,10 +34,12 @@
 #endif
 
 #include "alloc-util.h"
+#include "fd-util.h"
 #include "log.h"
 #include "macro.h"
 #include "path-util.h"
 #include "selinux-util.h"
+#include "stdio-util.h"
 #include "time-util.h"
 #include "util.h"
 
@@ -51,7 +53,8 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(context_t, context_free);
 static int cached_use = -1;
 static struct selabel_handle *label_hnd = NULL;
 
-#define log_enforcing(...) log_full_errno(security_getenforce() == 1 ? LOG_ERR : LOG_DEBUG, errno, __VA_ARGS__)
+#define log_enforcing(...) log_full(security_getenforce() == 1 ? LOG_ERR : LOG_DEBUG, __VA_ARGS__)
+#define log_enforcing_errno(r, ...) log_full_errno(security_getenforce() == 1 ? LOG_ERR : LOG_DEBUG, r, __VA_ARGS__)
 #endif
 
 bool mac_selinux_use(void) {
@@ -120,9 +123,12 @@ void mac_selinux_finish(void) {
 #endif
 }
 
-int mac_selinux_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
+int mac_selinux_fix(const char *path, LabelFixFlags flags) {
 
 #if HAVE_SELINUX
+        char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+        _cleanup_freecon_ char* fcon = NULL;
+        _cleanup_close_ int fd = -1;
         struct stat st;
         int r;
 
@@ -132,37 +138,55 @@ int mac_selinux_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
         if (!label_hnd)
                 return 0;
 
-        r = lstat(path, &st);
-        if (r >= 0) {
-                _cleanup_freecon_ char* fcon = NULL;
+        /* Open the file as O_PATH, to pin it while we determine and adjust the label */
+        fd = open(path, O_NOFOLLOW|O_CLOEXEC|O_PATH);
+        if (fd < 0) {
+                if ((flags & LABEL_IGNORE_ENOENT) && errno == ENOENT)
+                        return 0;
 
-                r = selabel_lookup_raw(label_hnd, &fcon, path, st.st_mode);
+                return -errno;
+        }
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (selabel_lookup_raw(label_hnd, &fcon, path, st.st_mode) < 0) {
+                r = -errno;
 
                 /* If there's no label to set, then exit without warning */
-                if (r < 0 && errno == ENOENT)
+                if (r == -ENOENT)
                         return 0;
 
-                if (r >= 0) {
-                        r = lsetfilecon_raw(path, fcon);
-
-                        /* If the FS doesn't support labels, then exit without warning */
-                        if (r < 0 && errno == EOPNOTSUPP)
-                                return 0;
-                }
+                goto fail;
         }
 
-        if (r < 0) {
-                /* Ignore ENOENT in some cases */
-                if (ignore_enoent && errno == ENOENT)
+        xsprintf(procfs_path, "/proc/self/fd/%i", fd);
+        if (setfilecon_raw(procfs_path, fcon) < 0) {
+                _cleanup_freecon_ char *oldcon = NULL;
+
+                r = -errno;
+
+                /* If the FS doesn't support labels, then exit without warning */
+                if (r == -EOPNOTSUPP)
                         return 0;
 
-                if (ignore_erofs && errno == EROFS)
+                /* It the FS is read-only and we were told to ignore failures caused by that, suppress error */
+                if (r == -EROFS && (flags & LABEL_IGNORE_EROFS))
                         return 0;
 
-                log_enforcing("Unable to fix SELinux security context of %s: %m", path);
-                if (security_getenforce() == 1)
-                        return -errno;
+                /* If the old label is identical to the new one, suppress any kind of error */
+                if (getfilecon_raw(procfs_path, &oldcon) >= 0 && streq(fcon, oldcon))
+                        return 0;
+
+                goto fail;
         }
+
+        return 0;
+
+fail:
+        log_enforcing_errno(r, "Unable to fix SELinux security context of %s: %m", path);
+        if (security_getenforce() == 1)
+                return r;
 #endif
 
         return 0;

diff --git a/src/basic/selinux-util.h b/src/basic/selinux-util.h
index 9780dca..1cb4ea4 100644 (file)
--- a/src/basic/selinux-util.h
+++ b/src/basic/selinux-util.h
@@ -25,6 +25,7 @@
 #include <sys/types.h>
 
 #include "macro.h"
+#include "label.h"
 
 bool mac_selinux_use(void);
 void mac_selinux_retest(void);
@@ -32,7 +33,7 @@ void mac_selinux_retest(void);
 int mac_selinux_init(void);
 void mac_selinux_finish(void);
 
-int mac_selinux_fix(const char *path, bool ignore_enoent, bool ignore_erofs);
+int mac_selinux_fix(const char *path, LabelFixFlags flags);
 int mac_selinux_apply(const char *path, const char *label);
 
 int mac_selinux_get_create_label_from_exe(const char *exe, char **label);

diff --git a/src/basic/smack-util.c b/src/basic/smack-util.c
index f0018f0..977de01 100644 (file)
--- a/src/basic/smack-util.c
+++ b/src/basic/smack-util.c
@@ -21,18 +21,21 @@
 ***/
 
 #include <errno.h>
+#include <fcntl.h>
 #include <string.h>
 #include <sys/stat.h>
 #include <sys/xattr.h>
 #include <unistd.h>
 
 #include "alloc-util.h"
+#include "fd-util.h"
 #include "fileio.h"
 #include "log.h"
 #include "macro.h"
 #include "path-util.h"
 #include "process-util.h"
 #include "smack-util.h"
+#include "stdio-util.h"
 #include "string-table.h"
 #include "xattr-util.h"
 
@@ -134,7 +137,10 @@ int mac_smack_apply_pid(pid_t pid, const char *label) {
         return r;
 }
 
-int mac_smack_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
+int mac_smack_fix(const char *path, LabelFixFlags flags) {
+        char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+        _cleanup_close_ int fd = -1;
+        const char *label;
         struct stat st;
         int r;
 
@@ -143,50 +149,59 @@ int mac_smack_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
         if (!mac_smack_use())
                 return 0;
 
-        /*
-         * Path must be in /dev and must exist
-         */
+        /* Path must be in /dev */
         if (!path_startswith(path, "/dev"))
                 return 0;
 
-        r = lstat(path, &st);
-        if (r >= 0) {
-                const char *label;
-
-                /*
-                 * Label directories and character devices "*".
-                 * Label symlinks "_".
-                 * Don't change anything else.
-                 */
-
-                if (S_ISDIR(st.st_mode))
-                        label = SMACK_STAR_LABEL;
-                else if (S_ISLNK(st.st_mode))
-                        label = SMACK_FLOOR_LABEL;
-                else if (S_ISCHR(st.st_mode))
-                        label = SMACK_STAR_LABEL;
-                else
+        fd = open(path, O_NOFOLLOW|O_CLOEXEC|O_PATH);
+        if (fd < 0) {
+                if ((flags & LABEL_IGNORE_ENOENT) && errno == ENOENT)
                         return 0;
 
-                r = lsetxattr(path, "security.SMACK64", label, strlen(label), 0);
+                return -errno;
+        }
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        /*
+         * Label directories and character devices "*".
+         * Label symlinks "_".
+         * Don't change anything else.
+         */
+
+        if (S_ISDIR(st.st_mode))
+                label = SMACK_STAR_LABEL;
+        else if (S_ISLNK(st.st_mode))
+                label = SMACK_FLOOR_LABEL;
+        else if (S_ISCHR(st.st_mode))
+                label = SMACK_STAR_LABEL;
+        else
+                return 0;
+
+        xsprintf(procfs_path, "/proc/self/fd/%i", fd);
+        if (setxattr(procfs_path, "security.SMACK64", label, strlen(label), 0) < 0) {
+                _cleanup_free_ char *old_label = NULL;
+
+                r = -errno;
 
                 /* If the FS doesn't support labels, then exit without warning */
-                if (r < 0 && errno == EOPNOTSUPP)
+                if (r == -EOPNOTSUPP)
                         return 0;
-        }
 
-        if (r < 0) {
-                /* Ignore ENOENT in some cases */
-                if (ignore_enoent && errno == ENOENT)
+                /* It the FS is read-only and we were told to ignore failures caused by that, suppress error */
+                if (r == -EROFS && (flags & LABEL_IGNORE_EROFS))
                         return 0;
 
-                if (ignore_erofs && errno == EROFS)
+                /* If the old label is identical to the new one, suppress any kind of error */
+                if (getxattr_malloc(procfs_path, "security.SMACK64", &old_label, false) >= 0 &&
+                    streq(old_label, label))
                         return 0;
 
-                r = log_debug_errno(errno, "Unable to fix SMACK label of %s: %m", path);
+                return log_debug_errno(r, "Unable to fix SMACK label of %s: %m", path);
         }
 
-        return r;
+        return 0;
 }
 
 int mac_smack_copy(const char *dest, const char *src) {

diff --git a/src/basic/smack-util.h b/src/basic/smack-util.h
index e4d46d7..58e6a54 100644 (file)
--- a/src/basic/smack-util.h
+++ b/src/basic/smack-util.h
@@ -25,25 +25,26 @@
 #include <stdbool.h>
 #include <sys/types.h>
 
+#include "label.h"
 #include "macro.h"
 
 #define SMACK_FLOOR_LABEL "_"
 #define SMACK_STAR_LABEL  "*"
 
 typedef enum SmackAttr {
-        SMACK_ATTR_ACCESS = 0,
-        SMACK_ATTR_EXEC = 1,
-        SMACK_ATTR_MMAP = 2,
-        SMACK_ATTR_TRANSMUTE = 3,
-        SMACK_ATTR_IPIN = 4,
-        SMACK_ATTR_IPOUT = 5,
+        SMACK_ATTR_ACCESS,
+        SMACK_ATTR_EXEC,
+        SMACK_ATTR_MMAP,
+        SMACK_ATTR_TRANSMUTE,
+        SMACK_ATTR_IPIN,
+        SMACK_ATTR_IPOUT,
         _SMACK_ATTR_MAX,
         _SMACK_ATTR_INVALID = -1,
 } SmackAttr;
 
 bool mac_smack_use(void);
 
-int mac_smack_fix(const char *path, bool ignore_enoent, bool ignore_erofs);
+int mac_smack_fix(const char *path, LabelFixFlags flags);
 
 const char* smack_attr_to_string(SmackAttr i) _const_;
 SmackAttr smack_attr_from_string(const char *s) _pure_;

diff --git a/src/core/automount.c b/src/core/automount.c
index a8d7736..bcc6b0b 100644 (file)
--- a/src/core/automount.c
+++ b/src/core/automount.c
@@ -346,7 +346,7 @@ static int open_dev_autofs(Manager *m) {
         if (m->dev_autofs_fd >= 0)
                 return m->dev_autofs_fd;
 
-        label_fix("/dev/autofs", false, false);
+        (void) label_fix("/dev/autofs", 0);
 
         m->dev_autofs_fd = open("/dev/autofs", O_CLOEXEC|O_RDONLY);
         if (m->dev_autofs_fd < 0)

diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c
index b7d6546..0fe794d 100644 (file)
--- a/src/core/mount-setup.c
+++ b/src/core/mount-setup.c
@@ -168,7 +168,7 @@ static int mount_one(const MountPoint *p, bool relabel) {
 
         /* Relabel first, just in case */
         if (relabel)
-                (void) label_fix(p->where, true, true);
+                (void) label_fix(p->where, LABEL_IGNORE_ENOENT|LABEL_IGNORE_EROFS);
 
         r = path_is_mount_point(p->where, NULL, AT_SYMLINK_FOLLOW);
         if (r < 0 && r != -ENOENT) {
@@ -206,7 +206,7 @@ static int mount_one(const MountPoint *p, bool relabel) {
 
         /* Relabel again, since we now mounted something fresh here */
         if (relabel)
-                (void) label_fix(p->where, false, false);
+                (void) label_fix(p->where, 0);
 
         if (p->mode & MNT_CHECK_WRITABLE) {
                 if (access(p->where, W_OK) < 0) {
@@ -374,7 +374,7 @@ static int nftw_cb(
         if (_unlikely_(ftwbuf->level == 0))
                 return FTW_CONTINUE;
 
-        label_fix(fpath, false, false);
+        (void) label_fix(fpath, 0);
 
         /* /run/initramfs is static data and big, no need to
          * dynamically relabel its contents at boot... */
@@ -413,7 +413,7 @@ int mount_setup(bool loaded_policy) {
                 r = cg_all_unified();
                 if (r == 0) {
                         (void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT, NULL);
-                        label_fix("/sys/fs/cgroup", false, false);
+                        (void) label_fix("/sys/fs/cgroup", 0);
                         nftw("/sys/fs/cgroup", nftw_cb, 64, FTW_MOUNT|FTW_PHYS|FTW_ACTIONRETVAL);
                         (void) mount(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT|MS_RDONLY, NULL);
                 } else if (r < 0)

diff --git a/src/hwdb/hwdb.c b/src/hwdb/hwdb.c
index f579ef7..a60809c 100644 (file)
--- a/src/hwdb/hwdb.c
+++ b/src/hwdb/hwdb.c
@@ -688,7 +688,7 @@ static int hwdb_update(int argc, char *argv[], void *userdata) {
         if (r < 0)
                 return log_error_errno(r, "Failure writing database %s: %m", hwdb_bin);
 
-        return label_fix(hwdb_bin, false, false);
+        return label_fix(hwdb_bin, 0);
 }
 
 static void help(void) {

diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index dc8feac..28574f4 100644 (file)
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -368,7 +368,7 @@ static int user_mkdir_runtime_path(User *u) {
                         }
                 }
 
-                r = label_fix(u->runtime_path, false, false);
+                r = label_fix(u->runtime_path, 0);
                 if (r < 0)
                         log_warning_errno(r, "Failed to fix label of '%s', ignoring: %m", u->runtime_path);
         }

diff --git a/src/tmpfiles/tmpfiles.c b/src/tmpfiles/tmpfiles.c
index b56b7ac..61e7657 100644 (file)
--- a/src/tmpfiles/tmpfiles.c
+++ b/src/tmpfiles/tmpfiles.c
@@ -850,7 +850,7 @@ static int fd_set_perms(Item *i, int fd, const struct stat *st) {
         }
 
 shortcut:
-        return label_fix(path, false, false);
+        return label_fix(path, 0);
 }
 
 static int path_set_perms(Item *i, const char *path) {

diff --git a/src/udev/udev-node.c b/src/udev/udev-node.c
index 6a3ee93..755bf66 100644 (file)
--- a/src/udev/udev-node.c
+++ b/src/udev/udev-node.c
@@ -79,7 +79,7 @@ static int node_symlink(struct udev_device *dev, const char *node, const char *s
                                 buf[len] = '\0';
                                 if (streq(target, buf)) {
                                         log_debug("preserve already existing symlink '%s' to '%s'", slink, target);
-                                        label_fix(slink, true, false);
+                                        (void) label_fix(slink, LABEL_IGNORE_ENOENT);
                                         utimensat(AT_FDCWD, slink, NULL, AT_SYMLINK_NOFOLLOW);
                                         goto exit;
                                 }
@@ -324,7 +324,7 @@ static int node_permissions_apply(struct udev_device *dev, bool apply,
 
                 /* set the defaults */
                 if (!selinux)
-                        mac_selinux_fix(devnode, true, false);
+                        (void) mac_selinux_fix(devnode, LABEL_IGNORE_ENOENT);
                 if (!smack)
                         mac_smack_apply(devnode, SMACK_ATTR_ACCESS, NULL);
         }

diff --git a/src/udev/udevadm-hwdb.c b/src/udev/udevadm-hwdb.c
index dc3ae74..3a5b138 100644 (file)
--- a/src/udev/udevadm-hwdb.c
+++ b/src/udev/udevadm-hwdb.c
@@ -680,7 +680,7 @@ static int adm_hwdb(struct udev *udev, int argc, char *argv[]) {
                         rc = EXIT_FAILURE;
                 }
 
-                label_fix(hwdb_bin, false, false);
+                (void) label_fix(hwdb_bin, 0);
         }
 
         if (test) {