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v260
src/shared/shift-uid.c
450 строк
16 KB
Daan De Meyer
shift-uid: Add debug logging
12 фев 2026, 11:46
12 фев 2026, 11:46
f933e95
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/* SPDX-License-Identifier: LGPL-2.1-or-later */ #include <linux/magic.h> #include <sys/statvfs.h> #include <unistd.h> #include "acl-util.h" #include "alloc-util.h" #include "dirent-util.h" #include "errno-util.h" #include "fd-util.h" #include "fileio.h" #include "fs-util.h" #include "log.h" #include "shift-uid.h" #include "stat-util.h" #include "string-util.h" #include "user-util.h" /* While we are chmod()ing a directory tree, we set the top-level UID base to this "busy" base, so that we can always * recognize trees we are were chmod()ing recursively and got interrupted in */ #define UID_BUSY_BASE ((uid_t) UINT32_C(0xFFFE0000)) #define UID_BUSY_MASK ((uid_t) UINT32_C(0xFFFF0000)) #if HAVE_ACL static int get_acl(int fd, const char *name, acl_type_t type, acl_t *ret) { acl_t acl; assert(fd >= 0); assert(ret); if (name) { _cleanup_close_ int child_fd = -EBADF; child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW); if (child_fd < 0) return -errno; acl = sym_acl_get_file(FORMAT_PROC_FD_PATH(child_fd), type); } else if (type == ACL_TYPE_ACCESS) acl = sym_acl_get_fd(fd); else acl = sym_acl_get_file(FORMAT_PROC_FD_PATH(fd), type); if (!acl) return -errno; *ret = acl; return 0; } static int set_acl(int fd, const char *name, acl_type_t type, acl_t acl) { int r; assert(fd >= 0); assert(acl); if (name) { _cleanup_close_ int child_fd = -EBADF; child_fd = openat(fd, name, O_PATH|O_CLOEXEC|O_NOFOLLOW); if (child_fd < 0) return -errno; r = sym_acl_set_file(FORMAT_PROC_FD_PATH(child_fd), type, acl); } else if (type == ACL_TYPE_ACCESS) r = sym_acl_set_fd(fd, acl); else r = sym_acl_set_file(FORMAT_PROC_FD_PATH(fd), type, acl); if (r < 0) return -errno; return 0; } static int shift_acl(acl_t acl, uid_t shift, acl_t *ret) { _cleanup_(acl_freep) acl_t copy = NULL; acl_entry_t i; int r; assert(acl); assert(ret); r = sym_acl_get_entry(acl, ACL_FIRST_ENTRY, &i); if (r < 0) return -errno; while (r > 0) { uid_t *old_uid, new_uid; bool modify = false; acl_tag_t tag; if (sym_acl_get_tag_type(i, &tag) < 0) return -errno; if (IN_SET(tag, ACL_USER, ACL_GROUP)) { /* We don't distinguish here between uid_t and gid_t, let's make sure the compiler checks that * this is actually OK */ assert_cc(sizeof(uid_t) == sizeof(gid_t)); old_uid = sym_acl_get_qualifier(i); if (!old_uid) return -errno; new_uid = shift | (*old_uid & UINT32_C(0xFFFF)); if (!uid_is_valid(new_uid)) return -EINVAL; modify = new_uid != *old_uid; if (modify && !copy) { int n; /* There's no copy of the ACL yet? if so, let's create one, and start the loop from the * beginning, so that we copy all entries, starting from the first, this time. */ n = sym_acl_entries(acl); if (n < 0) return -errno; copy = sym_acl_init(n); if (!copy) return -errno; /* Seek back to the beginning */ r = sym_acl_get_entry(acl, ACL_FIRST_ENTRY, &i); if (r < 0) return -errno; continue; } } if (copy) { acl_entry_t new_entry; if (sym_acl_create_entry(©, &new_entry) < 0) return -errno; if (sym_acl_copy_entry(new_entry, i) < 0) return -errno; if (modify) if (sym_acl_set_qualifier(new_entry, &new_uid) < 0) return -errno; } r = sym_acl_get_entry(acl, ACL_NEXT_ENTRY, &i); if (r < 0) return -errno; } *ret = TAKE_PTR(copy); return !!*ret; } static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) { _cleanup_(acl_freep) acl_t acl = NULL, shifted = NULL; bool changed = false; int r; assert(fd >= 0); assert(st); /* ACLs are not supported on symlinks, there's no point in trying */ if (!inode_type_can_acl(st->st_mode)) return 0; r = dlopen_libacl(); if (ERRNO_IS_NEG_NOT_SUPPORTED(r)) return 0; if (r < 0) return r; r = get_acl(fd, name, ACL_TYPE_ACCESS, &acl); if (r == -EOPNOTSUPP) return 0; if (r < 0) return r; r = shift_acl(acl, shift, &shifted); if (r < 0) return r; if (r > 0) { r = set_acl(fd, name, ACL_TYPE_ACCESS, shifted); if (r < 0) return r; changed = true; } if (S_ISDIR(st->st_mode)) { sym_acl_free(acl); if (shifted) sym_acl_free(shifted); acl = shifted = NULL; r = get_acl(fd, name, ACL_TYPE_DEFAULT, &acl); if (r < 0) return r; r = shift_acl(acl, shift, &shifted); if (r < 0) return r; if (r > 0) { r = set_acl(fd, name, ACL_TYPE_DEFAULT, shifted); if (r < 0) return r; changed = true; } } return changed; } #else static int patch_acls(int fd, const char *name, const struct stat *st, uid_t shift) { return 0; } #endif static int patch_fd(int fd, const char *name, const struct stat *st, uid_t shift) { uid_t new_uid; gid_t new_gid; bool changed = false; int r; assert(fd >= 0); assert(st); new_uid = shift | (st->st_uid & UINT32_C(0xFFFF)); new_gid = (gid_t) shift | (st->st_gid & UINT32_C(0xFFFF)); if (!uid_is_valid(new_uid) || !gid_is_valid(new_gid)) return -EINVAL; if (st->st_uid != new_uid || st->st_gid != new_gid) { if (name) r = fchownat(fd, name, new_uid, new_gid, AT_SYMLINK_NOFOLLOW); else r = fchown(fd, new_uid, new_gid); if (r < 0) return -errno; /* The Linux kernel alters the mode in some cases of chown(). Let's undo this. */ if (name) { if (!S_ISLNK(st->st_mode)) r = fchmodat(fd, name, st->st_mode, 0); else /* Changing the mode of a symlink is not supported by Linux kernel. Don't bother. */ r = 0; } else r = fchmod(fd, st->st_mode); if (r < 0) return -errno; changed = true; } r = patch_acls(fd, name, st, shift); if (r < 0) return r; return r > 0 || changed; } /* * Check if the filesystem is fully compatible with user namespaces or * UID/GID patching. Some filesystems in this list can be fully mounted inside * user namespaces, however their inodes may relate to host resources or only * valid in the global user namespace, therefore no patching should be applied. */ static int is_fs_fully_userns_compatible(const struct statfs *sfs) { assert(sfs); return F_TYPE_EQUAL(sfs->f_type, BINFMTFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, CGROUP_SUPER_MAGIC) || F_TYPE_EQUAL(sfs->f_type, CGROUP2_SUPER_MAGIC) || F_TYPE_EQUAL(sfs->f_type, DEBUGFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, DEVPTS_SUPER_MAGIC) || F_TYPE_EQUAL(sfs->f_type, EFIVARFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, HUGETLBFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, MQUEUE_MAGIC) || F_TYPE_EQUAL(sfs->f_type, PROC_SUPER_MAGIC) || F_TYPE_EQUAL(sfs->f_type, PSTOREFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, SELINUX_MAGIC) || F_TYPE_EQUAL(sfs->f_type, SMACK_MAGIC) || F_TYPE_EQUAL(sfs->f_type, SECURITYFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, BPF_FS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, TRACEFS_MAGIC) || F_TYPE_EQUAL(sfs->f_type, SYSFS_MAGIC); } static int recurse_fd(int fd, const struct stat *st, uid_t shift, bool is_toplevel) { _cleanup_closedir_ DIR *d = NULL; bool changed = false; struct statfs sfs; int r; assert(fd >= 0); if (fstatfs(fd, &sfs) < 0) return -errno; /* We generally want to permit crossing of mount boundaries when patching the UIDs/GIDs. However, we probably * shouldn't do this for /proc and /sys if that is already mounted into place. Hence, let's stop the recursion * when we hit procfs, sysfs or some other special file systems. */ r = is_fs_fully_userns_compatible(&sfs); if (r < 0) return r; if (r > 0) { r = 0; /* don't recurse */ return r; } /* Also, if we hit a read-only file system, then don't bother, skip the whole subtree */ if ((sfs.f_flags & ST_RDONLY) || access_fd(fd, W_OK) == -EROFS) goto read_only; if (S_ISDIR(st->st_mode)) { d = take_fdopendir(&fd); if (!d) return -errno; FOREACH_DIRENT_ALL(de, d, return -errno) { struct stat fst; if (dot_or_dot_dot(de->d_name)) continue; if (fstatat(dirfd(d), de->d_name, &fst, AT_SYMLINK_NOFOLLOW) < 0) return -errno; if (S_ISDIR(fst.st_mode)) { int subdir_fd; subdir_fd = openat(dirfd(d), de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME); if (subdir_fd < 0) return -errno; r = recurse_fd(subdir_fd, &fst, shift, false); if (r < 0) return r; if (r > 0) changed = true; } else { r = patch_fd(dirfd(d), de->d_name, &fst, shift); if (r < 0) return r; if (r > 0) changed = true; } } } /* After we descended, also patch the directory itself. It's key to do this in this order so that the top-level * directory is patched as very last object in the tree, so that we can use it as quick indicator whether the * tree is properly chown()ed already. */ r = patch_fd(d ? dirfd(d) : fd, NULL, st, shift); if (r == -EROFS) goto read_only; if (r > 0) changed = true; return changed; read_only: if (!is_toplevel) { _cleanup_free_ char *name = NULL; /* When we hit a read-only subtree we simply skip it, but log about it. */ (void) fd_get_path(fd, &name); log_debug("Skipping read-only file or directory %s.", strna(name)); r = changed; } return r; } int path_patch_uid(const char *path, uid_t shift, uid_t range) { _cleanup_close_ int fd = -EBADF; struct stat st; int r; assert(path); fd = open(path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME); if (fd < 0) return log_debug_errno(errno, "Failed to open '%s': %m", path); /* Recursively adjusts the UID/GIDs of all files of a directory tree. This is used to automatically fix up an * OS tree to the used user namespace UID range. Note that this automatic adjustment only works for UID ranges * following the concept that the upper 16-bit of a UID identify the container, and the lower 16-bit are the actual * UID within the container. */ /* We only support containers where the shift starts at a 2^16 boundary */ if ((shift & 0xFFFF) != 0) return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "UID shift 0x%"PRIx32" is not at a 2^16 boundary.", (uint32_t) shift); if (shift == UID_BUSY_BASE) return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "UID shift 0x%"PRIx32" conflicts with busy base.", (uint32_t) shift); /* We only support containers with 16-bit UID ranges for the patching logic */ if (range != 0x10000) return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "UID range 0x%"PRIx32" is not supported, must be 0x10000.", (uint32_t) range); if (fstat(fd, &st) < 0) return log_debug_errno(errno, "Failed to stat '%s': %m", path); /* We only support containers where the uid/gid container ID match */ if ((uint32_t) st.st_uid >> 16 != (uint32_t) st.st_gid >> 16) return log_debug_errno(SYNTHETIC_ERRNO(EBADE), "UID container ID 0x%"PRIx32" does not match GID container ID 0x%"PRIx32".", (uint32_t) st.st_uid >> 16, (uint32_t) st.st_gid >> 16); /* Try to detect if the range is already right. Of course, this a pretty drastic optimization, as we assume * that if the top-level dir has the right upper 16-bit assigned, then everything below will have too... */ if (((uint32_t) (st.st_uid ^ shift) >> 16) == 0) return 0; /* Before we start recursively chowning, mark the top-level dir as "busy" by chowning it to the "busy" * range. Should we be interrupted in the middle of our work, we'll see it owned by this user and will start * chown()ing it again, unconditionally, as the busy UID is not a valid UID we'd everpick for ourselves. */ if ((st.st_uid & UID_BUSY_MASK) != UID_BUSY_BASE) if (fchown(fd, UID_BUSY_BASE | (st.st_uid & ~UID_BUSY_MASK), (gid_t) UID_BUSY_BASE | (st.st_gid & ~(gid_t) UID_BUSY_MASK)) < 0) log_debug_errno(errno, "Failed to mark '%s' as busy, ignoring: %m", path); r = recurse_fd(TAKE_FD(fd), &st, shift, /* is_toplevel= */ true); if (r < 0) return log_debug_errno(r, "Failed to recursively patch UID/GID of '%s': %m", path); return r; }