From: Lennart Poettering Date: Tue, 27 Mar 2018 05:38:26 +0000 (+0200) Subject: label: rework label_fix() implementations (#8583) X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=commitdiff_plain;h=d3bc5662dd8436ea2ddcd49d18a48e9a4818bb44;p=elogind.git 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 50cdd8c73..d988dae04 100644 --- 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; @@ -62,7 +62,7 @@ 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) { @@ -80,6 +80,6 @@ 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); } #endif // 0 diff --git a/src/basic/label.h b/src/basic/label.h index 4bfcfe39f..cad224ce7 100644 --- a/src/basic/label.h +++ b/src/basic/label.h @@ -23,7 +23,12 @@ #include #include -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); #if 0 /// UNNEEDED by elogind diff --git a/src/basic/mkdir-label.c b/src/basic/mkdir-label.c index 4e5b7c961..6b4656669 100644 --- 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 5d782ab5d..955b8def7 100644 --- 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 4dfef4f06..ea7386cdf 100644 --- a/src/basic/selinux-util.h +++ b/src/basic/selinux-util.h @@ -25,6 +25,7 @@ #include #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); #if 0 /// UNNEEDED by elogind int mac_selinux_apply(const char *path, const char *label); diff --git a/src/basic/smack-util.c b/src/basic/smack-util.c index fc09226a5..682a612b1 100644 --- a/src/basic/smack-util.c +++ b/src/basic/smack-util.c @@ -21,18 +21,21 @@ ***/ #include +//#include #include #include #include #include #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" @@ -136,7 +139,10 @@ int mac_smack_apply_pid(pid_t pid, const char *label) { } #endif // 0 -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; @@ -145,50 +151,59 @@ 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; } #if 0 /// UNNEEDED by elogind diff --git a/src/basic/smack-util.h b/src/basic/smack-util.h index c691fdc12..6f8e3ea0c 100644 --- a/src/basic/smack-util.h +++ b/src/basic/smack-util.h @@ -25,6 +25,7 @@ #include #include +//#include "label.h" #include "macro.h" #define SMACK_FLOOR_LABEL "_" @@ -32,12 +33,12 @@ #if 0 /// UNNEEDED by elogind 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; @@ -45,7 +46,7 @@ typedef enum 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); #if 0 /// UNNEEDED by elogind const char* smack_attr_to_string(SmackAttr i) _const_; diff --git a/src/core/mount-setup.c b/src/core/mount-setup.c index 7073175e1..f53d2fca0 100644 --- a/src/core/mount-setup.c +++ b/src/core/mount-setup.c @@ -182,7 +182,7 @@ 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) { @@ -220,7 +220,7 @@ 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) { @@ -389,7 +389,7 @@ 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... */ @@ -430,7 +430,7 @@ 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/login/logind-user.c b/src/login/logind-user.c index 155ec6a5a..20b8601c1 100644 --- a/src/login/logind-user.c +++ b/src/login/logind-user.c @@ -374,7 +374,7 @@ 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); }