#include <ftw.h> /* nftw() et al. */
#include <getopt.h>
#include <libgen.h> /* basename(), dirname() */
+#include <limits.h> /* PATH_MAX */
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#define ACL_FAILURE 0
#define ACL_SUCCESS 1
-
+/* Even though most other library functions reliably return -1 for
+ * error, it feels a little wrong to re-use the ACL_ERROR constant.
+ */
+#define CLOSE_ERROR -1
+#define NFTW_ERROR -1
+#define OPEN_ERROR -1
+#define SNPRINTF_ERROR -1
+#define STAT_ERROR -1
/**
- * @brief Determine if the given file descriptor might refer to an
- * (unsafe) hard link.
+ * @brief The recursive portion of the @c safe_open function, used to
+ * open a file descriptor in a symlink-safe way when combined with
+ * the @c O_NOFOLLOW flag.
*
- * @param fd
- * The file descriptor whose link count we want to investigate.
+ * @param at_fd
+ * A file descriptor relative to which @c pathname will be opened.
*
- * @return true if we are certain that @c fd does not describe a hard
- * link, and false otherwise. In case of error, false is returned,
- * because we are not sure that @c fd is not a hard link.
+ * @param pathname
+ * The path to the file/directory/whatever whose descriptor you want.
+ *
+ * @return a file descriptor for @c pathname if everything goes well,
+ * and @c OPEN_ERROR if not.
*/
-bool is_hardlink_safe(int fd) {
- if (fd <= 0) {
- return false;
- }
- struct stat s;
- if (fstat(fd, &s) == 0) {
- return (s.st_nlink == 1 || S_ISDIR(s.st_mode));
- }
- else {
- return false;
- }
+int safe_open_ex(int at_fd, char* pathname, int flags) {
+ if (pathname != NULL && strlen(pathname) == 0) {
+ /* Oops, went one level to deep with nothing to do. */
+ return at_fd;
+ }
+
+ char* firstslash = strchr(pathname, '/');
+ if (firstslash == NULL) {
+ /* No more slashes, this is the base case. */
+ int r = openat(at_fd, pathname, flags);
+ return r;
+ }
+
+ /* Temporarily disable the slash, so that the subsequent call to
+ openat() opens only the next directory (and doesn't recurse). */
+ *firstslash = '\0';
+ int fd = safe_open_ex(at_fd, pathname, flags);
+ if (fd == OPEN_ERROR) {
+ if (errno != ELOOP) {
+ /* Don't output anything if we ignore a symlink */
+ perror("safe_open_ex (safe_open_ex)");
+ }
+ return OPEN_ERROR;
+ }
+
+ /* The ++ is safe because there needs to be at least a null byte
+ after the first slash, even if it's the last real character in
+ the string. */
+ int result = safe_open_ex(fd, firstslash+1, flags);
+ if (close(fd) == CLOSE_ERROR) {
+ perror("safe_open_ex (close)");
+ return OPEN_ERROR;
+ }
+ return result;
}
/**
- * @brief Determine whether or not the given file descriptor is for
- * a regular file.
+ * @brief A version of @c open that is completely symlink-safe when
+ * used with the @c O_NOFOLLOW flag.
*
- * @param fd
- * The file descriptor to test for regular-fileness.
+ * The @c openat function exists to ensure that you can anchor one
+ * path to a particular directory while opening it; however, if you
+ * open "b/c/d" relative to "/a", then even the @c openat function will
+ * still follow symlinks in the "b" component. This can be exploited
+ * by an attacker to make you open the wrong path.
*
- * @return true if @c fd describes a regular file, and false otherwise.
+ * To avoid that problem, this function uses a recursive
+ * implementation that opens every path from the root, one level at a
+ * time. So "a" is opened relative to "/", and then "b" is opened
+ * relative to "/a", and then "c" is opened relative to "/a/b",
+ * etc. When the @c O_NOFOLLOW flag is used, this approach ensures
+ * that no symlinks in any component are followed.
+ *
+ * @param pathname
+ * The path to the file/directory/whatever whose descriptor you want.
+ *
+ * @return a file descriptor for @c pathname if everything goes well,
+ * and @c OPEN_ERROR if not.
*/
-bool is_regular_file(int fd) {
- if (fd <= 0) {
- return false;
+int safe_open(const char* pathname, int flags) {
+ if (pathname == NULL || strlen(pathname) == 0 || pathname[0] == '\0') {
+ /* error? */
+ return OPEN_ERROR;
}
- struct stat s;
- if (fstat(fd, &s) == 0) {
- return S_ISREG(s.st_mode);
+ char abspath[PATH_MAX];
+ int snprintf_result = 0;
+ if (strchr(pathname, '/') == pathname) {
+ /* pathname is already absolute; just copy it. */
+ snprintf_result = snprintf(abspath, PATH_MAX, "%s", pathname);
}
else {
- return false;
+ /* Concatenate the current working directory and pathname into an
+ * absolute path. We use realpath() ONLY on the cwd part, and not
+ * on the pathname part, because realpath() resolves symlinks. And
+ * the whole point of all this crap is to avoid following symlinks
+ * in the pathname.
+ *
+ * Using realpath() on the cwd lets us operate on relative paths
+ * while we're sitting in a directory that happens to have a
+ * symlink in it; for example: cd /var/run && apply-default-acl foo.
+ */
+ char* cwd = get_current_dir_name();
+ if (cwd == NULL) {
+ perror("safe_open (get_current_dir_name)");
+ return OPEN_ERROR;
+ }
+
+ char abs_cwd[PATH_MAX];
+ if (realpath(cwd, abs_cwd) == NULL) {
+ perror("safe_open (realpath)");
+ free(cwd);
+ return OPEN_ERROR;
+ }
+ snprintf_result = snprintf(abspath, PATH_MAX, "%s/%s", abs_cwd, pathname);
+ free(cwd);
}
+ if (snprintf_result == SNPRINTF_ERROR || snprintf_result > PATH_MAX) {
+ perror("safe_open (snprintf)");
+ return OPEN_ERROR;
+ }
+
+ int fd = open("/", flags);
+ if (strcmp(abspath, "/") == 0) {
+ return fd;
+ }
+
+ int result = safe_open_ex(fd, abspath+1, flags);
+ if (close(fd) == CLOSE_ERROR) {
+ perror("safe_open (close)");
+ return OPEN_ERROR;
+ }
+ return result;
}
-/**
- * @brief Determine whether or not the given path is a directory.
- *
- * @param path
- * The path to test.
- *
- * @return true if @c path is a directory, false otherwise.
- */
-bool is_path_directory(const char* path) {
- if (path == NULL) {
- return false;
- }
-
- struct stat s;
- if (lstat(path, &s) == 0) {
- return S_ISDIR(s.st_mode);
- }
- else {
- return false;
- }
-}
-
-
-/**
- * @brief Determine whether or not the given file descriptor is for
- * a directory.
- *
- * @param fd
- * The file descriptor whose directoryness is in question.
- *
- * @return true if @c fd describes a directory, and false otherwise.
- */
-bool is_directory(int fd) {
- if (fd <= 0) {
- return false;
- }
-
- struct stat s;
- if (fstat(fd, &s) == 0) {
- return S_ISDIR(s.st_mode);
- }
- else {
- return false;
- }
-}
-
-
-
/**
* @brief Update (or create) an entry in an @b minimal ACL.
*
* returned. Otherwise, @c ACL_SUCCESS.
*
*/
-int acl_set_entry(acl_t* aclp,
- acl_entry_t entry) {
+int acl_set_entry(acl_t* aclp, acl_entry_t entry) {
acl_tag_t entry_tag;
if (acl_get_tag_type(entry, &entry_tag) == ACL_ERROR) {
/**
- * @brief Determine whether @c fd is executable (by anyone) or a
- * directory.
+ * @brief Determine whether @c fd is executable by anyone.
+ *
*
* This is used as part of the heuristic to determine whether or not
* we should mask the execute bit when inheriting an ACL. If @c fd
- * describes a directory, the answer is a clear-cut yes. This behavior
- * is modeled after the capital 'X' perms of setfacl.
- *
- * If @c fd describes a file, we check the @a effective permissions,
- * contrary to what setfacl does.
+ * describes a file, we check the @a effective permissions, contrary
+ * to what setfacl does.
*
* @param fd
* The file descriptor to check.
*
+ * @param sp
+ * A pointer to a stat structure for @c fd.
+ *
* @return
- * - @c ACL_SUCCESS - @c fd describes a directory, or someone has effective
- execute permissions.
- * - @c ACL_FAILURE - @c fd describes a regular file and nobody can execute
- it.
+ * - @c ACL_SUCCESS - Someone has effective execute permissions on @c fd.
+ * - @c ACL_FAILURE - Nobody can execute @c fd.
* - @c ACL_ERROR - Unexpected library error.
*/
-int any_can_execute_or_dir(int fd) {
-
- if (is_directory(fd)) {
- /* That was easy... */
- return ACL_SUCCESS;
- }
-
+int any_can_execute(int fd, const struct stat* sp) {
acl_t acl = acl_get_fd(fd);
if (acl == (acl_t)NULL) {
- perror("any_can_execute_or_dir (acl_get_file)");
+ perror("any_can_execute (acl_get_file)");
return ACL_ERROR;
}
int result = ACL_FAILURE;
if (acl_is_minimal(acl)) {
- struct stat s;
- if (fstat(fd, &s) == -1) {
- perror("any_can_execute_or_dir (fstat)");
- result = ACL_ERROR;
- goto cleanup;
- }
- if (s.st_mode & (S_IXUSR | S_IXOTH | S_IXGRP)) {
+ if (sp->st_mode & (S_IXUSR | S_IXOTH | S_IXGRP)) {
result = ACL_SUCCESS;
goto cleanup;
}
acl_tag_t tag = ACL_UNDEFINED_TAG;
if (acl_get_tag_type(entry, &tag) == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_tag_type)");
+ perror("any_can_execute_or (acl_get_tag_type)");
result = ACL_ERROR;
goto cleanup;
}
acl_permset_t permset;
if (acl_get_permset(entry, &permset) == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_permset)");
+ perror("any_can_execute_or (acl_get_permset)");
result = ACL_ERROR;
goto cleanup;
}
int gp_result = acl_get_perm(permset, ACL_EXECUTE);
if (gp_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_perm)");
+ perror("any_can_execute (acl_get_perm)");
result = ACL_ERROR;
goto cleanup;
}
}
if (ge_result == ACL_ERROR) {
- perror("any_can_execute_or_dir (acl_get_entry)");
+ perror("any_can_execute (acl_get_entry)");
result = ACL_ERROR;
goto cleanup;
}
/**
- * @brief Set @c acl as the default ACL on @c path if it's a directory.
+ * @brief Set @c acl as the default ACL on @c path.
*
- * This overwrites any existing default ACL on @c path. If no default
- * ACL exists, then one is created. If @c path is not a directory, we
- * return ACL_FAILURE but no error is raised.
+ * This overwrites any existing default ACL on @c path. If @c path is
+ * not a directory, we return ACL_ERROR and @c errno is set.
*
* @param path
* The target directory whose ACL we wish to replace or create.
*
* @return
* - @c ACL_SUCCESS - The default ACL was assigned successfully.
- * - @c ACL_FAILURE - If @c path is not a directory.
* - @c ACL_ERROR - Unexpected library error.
*/
int assign_default_acl(const char* path, acl_t acl) {
if (path == NULL) {
- errno = ENOENT;
+ errno = EINVAL;
+ perror("assign_default_acl (args)");
return ACL_ERROR;
}
- if (!is_path_directory(path)) {
- return ACL_FAILURE;
- }
-
- /* Our return value; success unless something bad happens. */
+ /* Our return value; success unless something bad happens. */
int result = ACL_SUCCESS;
acl_t path_acl = acl_dup(acl);
* @param path
* The path whose ACL we would like to reset to its default.
*
+ * @param sp
+ * A pointer to a stat structure for @c path, or @c NULL if you don't
+ * have one handy.
+ *
* @param no_exec_mask
* The value (either true or false) of the --no-exec-mask flag.
*
* or the parent of @c path is not a directory.
* - @c ACL_ERROR - Unexpected library error.
*/
-int apply_default_acl(const char* path, bool no_exec_mask) {
+int apply_default_acl(const char* path,
+ const struct stat* sp,
+ bool no_exec_mask) {
if (path == NULL) {
- errno = ENOENT;
+ errno = EINVAL;
+ perror("apply_default_acl (args)");
return ACL_ERROR;
}
/* The file descriptor corresponding to "path" */
int fd = 0;
- /* Split "path" into base/dirname parts to be used with openat().
- * We duplicate the strings involved because dirname/basename mangle
- * their arguments.
+ /* Get the parent directory of "path" with dirname(), which happens
+ * to murder its argument and necessitates a path_copy.
*/
char* path_copy = strdup(path);
if (path_copy == NULL) {
}
char* parent = dirname(path_copy);
- fd = open(path, O_NOFOLLOW);
- if (fd == -1) {
+ fd = safe_open(path, O_NOFOLLOW);
+ if (fd == OPEN_ERROR) {
if (errno == ELOOP) {
result = ACL_FAILURE; /* hit a symlink */
goto cleanup;
* race condition here, but the window is as small as possible
* between when we open the file descriptor (look above) and when we
* fstat it.
+ *
+ * Note: we only need to call fstat ourselves if we weren't passed a
+ * valid pointer to a stat structure (nftw does that).
*/
- if (!is_hardlink_safe(fd)) {
- result = ACL_FAILURE;
- goto cleanup;
+ if (sp == NULL) {
+ struct stat s;
+ if (fstat(fd, &s) == STAT_ERROR) {
+ perror("apply_default_acl (fstat)");
+ goto cleanup;
+ }
+
+ sp = &s;
}
- if (!is_regular_file(fd) && !is_directory(fd)) {
- result = ACL_FAILURE;
- goto cleanup;
+ if (!S_ISDIR(sp->st_mode)) {
+ /* If it's not a directory, make sure it's a regular,
+ non-hard-linked file. */
+ if (!S_ISREG(sp->st_mode) || sp->st_nlink != 1) {
+ result = ACL_FAILURE;
+ goto cleanup;
+ }
}
+
/* Default to not masking the exec bit; i.e. applying the default
ACL literally. If --no-exec-mask was not specified, then we try
- to "guess" whether or not to mask the exec bit. */
+ to "guess" whether or not to mask the exec bit. This behavior
+ is modeled after the capital 'X' perms of setfacl. */
bool allow_exec = true;
if (!no_exec_mask) {
- int ace_result = any_can_execute_or_dir(fd);
+ /* Never mask the execute bit on directories. */
+ int ace_result = any_can_execute(fd,sp) || S_ISDIR(sp->st_mode);
if (ace_result == ACL_ERROR) {
- perror("apply_default_acl (any_can_execute_or_dir)");
+ perror("apply_default_acl (any_can_execute)");
result = ACL_ERROR;
goto cleanup;
}
goto cleanup;
}
- /* If it's a directory, inherit the parent's default. */
- if (assign_default_acl(path, defacl) == ACL_ERROR) {
+ /* If it's a directory, inherit the parent's default. We sure hope
+ * that "path" still points to the same thing that "fd" and this
+ * "sp" describe. If not, we may wind up trying to set a default ACL
+ * on a file, and this will throw an error. I guess that's what we
+ * want to do?
+ */
+ if (S_ISDIR(sp->st_mode) && assign_default_acl(path, defacl) == ACL_ERROR) {
perror("apply_default_acl (assign_default_acl)");
result = ACL_ERROR;
goto cleanup;
if (defacl != (acl_t)NULL) {
acl_free(defacl);
}
- if (fd >= 0 && close(fd) == -1) {
+ if (fd >= 0 && close(fd) == CLOSE_ERROR) {
perror("apply_default_acl (close)");
result = ACL_ERROR;
}
*
*/
int apply_default_acl_nftw(const char *target,
- const struct stat *s,
+ const struct stat *sp,
int info,
struct FTW *ftw) {
- if (apply_default_acl(target, false)) {
+ if (apply_default_acl(target, sp, false)) {
return FTW_CONTINUE;
}
else {
*
*/
int apply_default_acl_nftw_x(const char *target,
- const struct stat *s,
+ const struct stat *sp,
int info,
struct FTW *ftw) {
- if (apply_default_acl(target, true)) {
+ if (apply_default_acl(target, sp, true)) {
return FTW_CONTINUE;
}
else {
* we still return @c false.
*/
bool apply_default_acl_recursive(const char *target, bool no_exec_mask) {
-
- if (!is_path_directory(target)) {
- return apply_default_acl(target, no_exec_mask);
- }
-
int max_levels = 256;
int flags = FTW_PHYS; /* Don't follow links. */
return true;
}
- /* nftw will return -1 on error, or if the supplied function
+ /* nftw will return NFTW_ERROR on error, or if the supplied function
* (apply_default_acl_nftw) returns a non-zero result, nftw will
* return that.
*/
- if (nftw_result == -1) {
+ if (nftw_result == NFTW_ERROR) {
perror("apply_default_acl_recursive (nftw)");
}
}
else {
/* It's either a normal file, or we're not operating recursively. */
- reapp_result = apply_default_acl(target, no_exec_mask);
+ reapp_result = apply_default_acl(target, NULL, no_exec_mask);
}
if (!reapp_result) {
projects / apply-default-acl.git / blobdiff