Re: git: 6e69612d5df1 - main - pam: Add pam_xdg module
Date: Fri, 01 Mar 2024 21:36:09 UTC
Shawn Webb wrote in <q3t5ecjw7zrvswhwpqo7bcpoapfxn6unobsugfmwbtuyoifumn@kdamffwcyt4a>: ... |A defensive programming technique commonly implemented in functions |that recurse is to place a limit on how many times we recurse. | |HardenedBSD now places an arbitrarily picked limit of 1000 recursions: |https://git.hardenedbsd.org/hardenedbsd/HardenedBSD/-/commit/148478d5743\ |a8dd4362fd31dca4371618716d0a8 | |The limit can be changed at compile-time by defining |REMOVEDIR_MAX_RECUR to a different integer value. For context, the thing is around the time when i developed pam_xdg (ie: the real one!) systemd had a CVE in exactly its rm_rf code. I then downloaded the file and found that on Linux a graceful rm(1) -rf is too heavy for this simple module, and in particular subject to bitrot, and so i used system(3) (possibly for the first time ever in C -- not perl -- code; i have a SMP::Child myself). (Like that it can possibly last unchanged, now that i tweaked one string concatenation that was impossible initially.) /* SPDX-License-Identifier: LGPL-2.1-or-later */ #include <errno.h> #include <fcntl.h> #include <stdbool.h> #include <stddef.h> #include <unistd.h> #include "alloc-util.h" #include "btrfs-util.h" #include "cgroup-util.h" #include "dirent-util.h" #include "fd-util.h" #include "log.h" #include "macro.h" #include "mountpoint-util.h" #include "path-util.h" #include "rm-rf.h" #include "stat-util.h" #include "string-util.h" /* We treat tmpfs/ramfs + cgroupfs as non-physical file systems. cgroupfs is similar to tmpfs in a way * after all: we can create arbitrary directory hierarchies in it, and hence can also use rm_rf() on it * to remove those again. */ static bool is_physical_fs(const struct statfs *sfs) { return !is_temporary_fs(sfs) && !is_cgroup_fs(sfs); } static int patch_dirfd_mode( int dfd, mode_t *ret_old_mode) { struct stat st; assert(dfd >= 0); assert(ret_old_mode); if (fstat(dfd, &st) < 0) return -errno; if (!S_ISDIR(st.st_mode)) return -ENOTDIR; if (FLAGS_SET(st.st_mode, 0700)) /* Already set? */ return -EACCES; /* original error */ if (st.st_uid != geteuid()) /* this only works if the UID matches ours */ return -EACCES; if (fchmod(dfd, (st.st_mode | 0700) & 07777) < 0) return -errno; *ret_old_mode = st.st_mode; return 0; } int unlinkat_harder(int dfd, const char *filename, int unlink_flags, RemoveFlags remove_flags) { mode_t old_mode; int r; /* Like unlinkat(), but tries harder: if we get EACCESS we'll try to set the r/w/x bits on the * directory. This is useful if we run unprivileged and have some files where the w bit is * missing. */ if (unlinkat(dfd, filename, unlink_flags) >= 0) return 0; if (errno != EACCES || !FLAGS_SET(remove_flags, REMOVE_CHMOD)) return -errno; r = patch_dirfd_mode(dfd, &old_mode); if (r < 0) return r; if (unlinkat(dfd, filename, unlink_flags) < 0) { r = -errno; /* Try to restore the original access mode if this didn't work */ (void) fchmod(dfd, old_mode); return r; } if (FLAGS_SET(remove_flags, REMOVE_CHMOD_RESTORE) && fchmod(dfd, old_mode) < 0) return -errno; /* If this worked, we won't reset the old mode by default, since we'll need it for other entries too, * and we should destroy the whole thing */ return 0; } int fstatat_harder(int dfd, const char *filename, struct stat *ret, int fstatat_flags, RemoveFlags remove_flags) { mode_t old_mode; int r; /* Like unlink_harder() but does the same for fstatat() */ if (fstatat(dfd, filename, ret, fstatat_flags) >= 0) return 0; if (errno != EACCES || !FLAGS_SET(remove_flags, REMOVE_CHMOD)) return -errno; r = patch_dirfd_mode(dfd, &old_mode); if (r < 0) return r; if (fstatat(dfd, filename, ret, fstatat_flags) < 0) { r = -errno; (void) fchmod(dfd, old_mode); return r; } if (FLAGS_SET(remove_flags, REMOVE_CHMOD_RESTORE) && fchmod(dfd, old_mode) < 0) return -errno; return 0; } static int rm_rf_inner_child( int fd, const char *fname, int is_dir, RemoveFlags flags, const struct stat *root_dev, bool allow_recursion) { struct stat st; int r, q = 0; assert(fd >= 0); assert(fname); if (is_dir < 0 || root_dev || (is_dir > 0 && (root_dev || (flags & REMOVE_SUBVOLUME)))) { r = fstatat_harder(fd, fname, &st, AT_SYMLINK_NOFOLLOW, flags); if (r < 0) return r; is_dir = S_ISDIR(st.st_mode); } if (is_dir) { /* If root_dev is set, remove subdirectories only if device is same */ if (root_dev && st.st_dev != root_dev->st_dev) return 0; /* Stop at mount points */ r = fd_is_mount_point(fd, fname, 0); if (r < 0) return r; if (r > 0) return 0; if ((flags & REMOVE_SUBVOLUME) && btrfs_might_be_subvol(&st)) { /* This could be a subvolume, try to remove it */ r = btrfs_subvol_remove_fd(fd, fname, BTRFS_REMOVE_RECURSIVE|BTRFS_REMOVE_QUOTA); if (r < 0) { if (!IN_SET(r, -ENOTTY, -EINVAL)) return r; /* ENOTTY, then it wasn't a btrfs subvolume, continue below. */ } else /* It was a subvolume, done. */ return 1; } if (!allow_recursion) return -EISDIR; int subdir_fd = openat(fd, fname, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME); if (subdir_fd < 0) return -errno; /* We pass REMOVE_PHYSICAL here, to avoid doing the fstatfs() to check the file system type * again for each directory */ q = rm_rf_children(subdir_fd, flags | REMOVE_PHYSICAL, root_dev); } else if (flags & REMOVE_ONLY_DIRECTORIES) return 0; r = unlinkat_harder(fd, fname, is_dir ? AT_REMOVEDIR : 0, flags); if (r < 0) return r; if (q < 0) return q; return 1; } typedef struct TodoEntry { DIR *dir; /* A directory that we were operating on. */ char *dirname; /* The filename of that directory itself. */ } TodoEntry; static void free_todo_entries(TodoEntry **todos) { for (TodoEntry *x = *todos; x && x->dir; x++) { closedir(x->dir); free(x->dirname); } freep(todos); } int rm_rf_children( int fd, RemoveFlags flags, const struct stat *root_dev) { _cleanup_(free_todo_entries) TodoEntry *todos = NULL; size_t n_todo = 0; _cleanup_free_ char *dirname = NULL; /* Set when we are recursing and want to delete ourselves */ int ret = 0, r; /* Return the first error we run into, but nevertheless try to go on. * The passed fd is closed in all cases, including on failure. */ for (;;) { /* This loop corresponds to the directory nesting level. */ _cleanup_closedir_ DIR *d = NULL; if (n_todo > 0) { /* We know that we are in recursion here, because n_todo is set. * We need to remove the inner directory we were operating on. */ assert(dirname); r = unlinkat_harder(dirfd(todos[n_todo-1].dir), dirname, AT_REMOVEDIR, flags); if (r < 0 && r != -ENOENT && ret == 0) ret = r; dirname = mfree(dirname); /* And now let's back out one level up */ n_todo --; d = TAKE_PTR(todos[n_todo].dir); dirname = TAKE_PTR(todos[n_todo].dirname); assert(d); fd = dirfd(d); /* Retrieve the file descriptor from the DIR object */ assert(fd >= 0); } else { next_fd: assert(fd >= 0); d = fdopendir(fd); if (!d) { safe_close(fd); return -errno; } fd = dirfd(d); /* We donated the fd to fdopendir(). Let's make sure we sure we have * the right descriptor even if it were to internally invalidate the * one we passed. */ if (!(flags & REMOVE_PHYSICAL)) { struct statfs sfs; if (fstatfs(fd, &sfs) < 0) return -errno; if (is_physical_fs(&sfs)) { /* We refuse to clean physical file systems with this call, unless * explicitly requested. This is extra paranoia just to be sure we * never ever remove non-state data. */ _cleanup_free_ char *path = NULL; (void) fd_get_path(fd, &path); return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Attempted to remove disk file system under \"%s\", and we can't allow that.", strna(path)); } } } FOREACH_DIRENT_ALL(de, d, return -errno) { int is_dir; if (dot_or_dot_dot(de->d_name)) continue; is_dir = de->d_type == DT_UNKNOWN ? -1 : de->d_type == DT_DIR; r = rm_rf_inner_child(fd, de->d_name, is_dir, flags, root_dev, false); if (r == -EISDIR) { /* Push the current working state onto the todo list */ if (!GREEDY_REALLOC0(todos, n_todo + 2)) return log_oom(); _cleanup_free_ char *newdirname = strdup(de->d_name); if (!newdirname) return log_oom(); int newfd = openat(fd, de->d_name, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME); if (newfd >= 0) { todos[n_todo++] = (TodoEntry) { TAKE_PTR(d), TAKE_PTR(dirname) }; fd = newfd; dirname = TAKE_PTR(newdirname); goto next_fd; } else if (errno != -ENOENT && ret == 0) ret = -errno; } else if (r < 0 && r != -ENOENT && ret == 0) ret = r; } if (FLAGS_SET(flags, REMOVE_SYNCFS) && syncfs(fd) < 0 && ret >= 0) ret = -errno; if (n_todo == 0) break; } return ret; } int rm_rf(const char *path, RemoveFlags flags) { int fd, r, q = 0; assert(path); /* For now, don't support dropping subvols when also only dropping directories, since we can't do * this race-freely. */ if (FLAGS_SET(flags, REMOVE_ONLY_DIRECTORIES|REMOVE_SUBVOLUME)) return -EINVAL; /* We refuse to clean the root file system with this call. This is extra paranoia to never cause a * really seriously broken system. */ if (path_equal_or_files_same(path, "/", AT_SYMLINK_NOFOLLOW)) return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Attempted to remove entire root file system (\"%s\"), and we can't allow that.", path); if (FLAGS_SET(flags, REMOVE_SUBVOLUME | REMOVE_ROOT | REMOVE_PHYSICAL)) { /* Try to remove as subvolume first */ r = btrfs_subvol_remove(path, BTRFS_REMOVE_RECURSIVE|BTRFS_REMOVE_QUOTA); if (r >= 0) return r; if (FLAGS_SET(flags, REMOVE_MISSING_OK) && r == -ENOENT) return 0; if (!IN_SET(r, -ENOTTY, -EINVAL, -ENOTDIR)) return r; /* Not btrfs or not a subvolume */ } fd = open(path, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC|O_NOFOLLOW|O_NOATIME); if (fd >= 0) { /* We have a dir */ r = rm_rf_children(fd, flags, NULL); if (FLAGS_SET(flags, REMOVE_ROOT)) q = RET_NERRNO(rmdir(path)); } else { if (FLAGS_SET(flags, REMOVE_MISSING_OK) && errno == ENOENT) return 0; if (!IN_SET(errno, ENOTDIR, ELOOP)) return -errno; if (FLAGS_SET(flags, REMOVE_ONLY_DIRECTORIES) || !FLAGS_SET(flags, REMOVE_ROOT)) return 0; if (!FLAGS_SET(flags, REMOVE_PHYSICAL)) { struct statfs s; if (statfs(path, &s) < 0) return -errno; if (is_physical_fs(&s)) return log_error_errno(SYNTHETIC_ERRNO(EPERM), "Attempted to remove files from a disk file system under \"%s\", refusing.", path); } r = 0; q = RET_NERRNO(unlink(path)); } if (r < 0) return r; if (q < 0 && (q != -ENOENT || !FLAGS_SET(flags, REMOVE_MISSING_OK))) return q; return 0; } int rm_rf_child(int fd, const char *name, RemoveFlags flags) { /* Removes one specific child of the specified directory */ if (fd < 0) return -EBADF; if (!filename_is_valid(name)) return -EINVAL; if ((flags & (REMOVE_ROOT|REMOVE_MISSING_OK)) != 0) /* Doesn't really make sense here, we are not supposed to remove 'fd' anyway */ return -EINVAL; if (FLAGS_SET(flags, REMOVE_ONLY_DIRECTORIES|REMOVE_SUBVOLUME)) return -EINVAL; return rm_rf_inner_child(fd, name, -1, flags, NULL, true); } --steffen | |Der Kragenbaer, The moon bear, |der holt sich munter he cheerfully and one by one |einen nach dem anderen runter wa.ks himself off |(By Robert Gernhardt)