#define _GNU_SOURCE
#include <errno.h>
+#include <fcntl.h> /* AT_FOO constants */
#include <ftw.h> /* nftw() et al. */
#include <getopt.h>
#include <libgen.h> /* dirname() */
#define ACL_SUCCESS 1
-/* Command-line options */
-static bool no_exec_mask = false;
-
-
/**
* @brief Get the mode bits from the given path.
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return s.st_mode;
}
else {
- /* errno will be set already by stat() */
+ /* errno will be set already by lstat() */
return result;
}
}
+/**
+ * @brief Determine if the given path might refer to an (unsafe) hard link.
+ *
+ * @param path
+ * The path to test.
+ *
+ * @return true if we are certain that @c path does not refer to a hard
+ * link, and false otherwise. In case of error, false is returned,
+ * because we are not sure that @c path is not a hard link.
+ */
+bool is_hardlink_safe(const char* path) {
+ if (path == NULL) {
+ return false;
+ }
+ struct stat s;
+ int result = lstat(path, &s);
+ if (result == 0) {
+ return (s.st_nlink == 1 || S_ISDIR(s.st_mode));
+ }
+ else {
+ return false;
+ }
+}
+
+
/**
* @brief Determine whether or not the given path is a regular file.
*
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return S_ISREG(s.st_mode);
}
+/**
+ * @brief Determine whether or not the given path is accessible.
+ *
+ * @param path
+ * The path to test.
+ *
+ * @return true if @c path is accessible to the current effective
+ * user/group, false otherwise.
+ */
+bool path_accessible(const char* path) {
+ if (path == NULL) {
+ return false;
+ }
+
+ /* Test for access using the effective user and group rather than
+ the real one. */
+ int flags = AT_EACCESS;
+
+ /* Don't follow symlinks when checking for a path's existence,
+ since we won't follow them to set its ACLs either. */
+ flags |= AT_SYMLINK_NOFOLLOW;
+
+ /* If the path is relative, interpret it relative to the current
+ working directory (just like the access() system call). */
+ int result = faccessat(AT_FDCWD, path, F_OK, flags);
+
+ if (result == 0) {
+ return true;
+ }
+ else {
+ return false;
+ }
+}
+
+
+
/**
* @brief Determine whether or not the given path is a directory.
*
}
struct stat s;
- int result = stat(path, &s);
+ int result = lstat(path, &s);
if (result == 0) {
return S_ISDIR(s.st_mode);
}
}
+
/**
* @brief Determine whether @c path is executable (by anyone) or a
* directory.
int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry);
while (ge_result == ACL_SUCCESS) {
+ /* The first thing we do is check to see if this is a mask
+ entry. If it is, we skip it entirely. */
+ acl_tag_t tag = ACL_UNDEFINED_TAG;
+ int tag_result = acl_get_tag_type(entry, &tag);
+
+ if (tag_result == ACL_ERROR) {
+ perror("any_can_execute_or_dir (acl_get_tag_type)");
+ result = ACL_ERROR;
+ goto cleanup;
+ }
+
+ if (tag == ACL_MASK) {
+ ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry);
+ continue;
+ }
+
+ /* Ok, so it's not a mask entry. Check the execute perms. */
acl_permset_t permset;
int ps_result = acl_get_permset(entry, &permset);
}
if (gp_result == ACL_SUCCESS) {
- /* Only return one if this execute bit is not masked. */
+ /* Only return ACL_SUCCESS if this execute bit is not masked. */
if (acl_execute_masked(path) != ACL_SUCCESS) {
result = ACL_SUCCESS;
goto cleanup;
* @param path
* The path whose ACL we would like to reset to its default.
*
+ * @param no_exec_mask
+ * The value (either true or false) of the --no-exec-mask flag.
+ *
* @return
* - @c ACL_SUCCESS - The parent default ACL was inherited successfully.
* - @c ACL_FAILURE - The target path is not a regular file/directory,
* or the parent of @c path is not a directory.
* - @c ACL_ERROR - Unexpected library error.
*/
-int apply_default_acl(const char* path) {
+int apply_default_acl(const char* path, bool no_exec_mask) {
if (path == NULL) {
errno = ENOENT;
return ACL_ERROR;
}
+ /* Refuse to operate on hard links, which can be abused by an
+ * attacker to trick us into changing the ACL on a file we didn't
+ * intend to; namely the "target" of the hard link. To truly prevent
+ * that sort of mischief, we should be using file descriptors for
+ * the target and its parent directory. Then modulo a tiny race
+ * condition, we would be sure that "path" and "parent" don't change
+ * their nature between the time that we test them and when we
+ * utilize them. For contrast, the same attacker is free to replace
+ * "path" with a hard link after is_hardlink_safe() has returned
+ * "true" below.
+ *
+ * Unfortunately, our API is lacking in this area. For example,
+ * acl_set_fd() is only capable of setting the ACL_TYPE_ACCESS list,
+ * and not the ACL_TYPE_DEFAULT. Apparently the only way to operate
+ * on default ACLs is through the path name, which is inherently
+ * unreliable since the acl_*_file() calls themselves might follow
+ * links (both hard and symbolic).
+ *
+ * Some improvement could still be made by using descriptors where
+ * possible -- this would shrink the exploit window -- but for now
+ * we use a naive implementation that only keeps honest men honest.
+ */
+ if (!is_hardlink_safe(path)) {
+ return ACL_FAILURE;
+ }
+
if (!is_regular_file(path) && !is_directory(path)) {
return ACL_FAILURE;
}
* The program name to use in the output.
*
*/
-void usage(char* program_name) {
+void usage(const char* program_name) {
printf("Apply any applicable default ACLs to the given files or "
"directories.\n\n");
printf("Usage: %s [flags] <target1> [<target2> [ <target3>...]]\n\n",
int info,
struct FTW *ftw) {
- bool app_result = apply_default_acl(target);
+ bool app_result = apply_default_acl(target, false);
+ if (app_result) {
+ return FTW_CONTINUE;
+ }
+ else {
+ return FTW_STOP;
+ }
+}
+
+
+
+/**
+ * @brief Wrapper around @c apply_default_acl() for use with @c nftw().
+ *
+ * This is identical to @c apply_default_acl_nftw(), except it passes
+ * @c true to @c apply_default_acl() as its no_exec_mask argument.
+ *
+ */
+int apply_default_acl_nftw_x(const char *target,
+ const struct stat *s,
+ int info,
+ struct FTW *ftw) {
+
+ bool app_result = apply_default_acl(target, true);
if (app_result) {
return FTW_CONTINUE;
}
*
* We ignore symlinks for consistency with chmod -r.
*
+ * @param target
+ * The root (path) of the recursive application.
+ *
+ * @param no_exec_mask
+ * The value (either true or false) of the --no-exec-mask flag.
+ *
* @return
* If @c target is not a directory, we return the result of
* calling @c apply_default_acl() on @c target. Otherwise, we convert
* If there is an error, it will be reported via @c perror, but
* we still return @c false.
*/
-bool apply_default_acl_recursive(const char *target) {
+bool apply_default_acl_recursive(const char *target, bool no_exec_mask) {
if (!is_directory(target)) {
- return apply_default_acl(target);
+ return apply_default_acl(target, no_exec_mask);
}
int max_levels = 256;
int flags = FTW_PHYS; /* Don't follow links. */
- int nftw_result = nftw(target,
- apply_default_acl_nftw,
- max_levels,
- flags);
+ /* There are two separate functions that could be passed to
+ nftw(). One passes no_exec_mask = true to apply_default_acl(),
+ and the other passes no_exec_mask = false. Since the function we
+ pass to nftw() cannot have parameters, we have to create separate
+ options and make the decision here. */
+ int (*fn)(const char *, const struct stat *, int, struct FTW *) = NULL;
+ fn = no_exec_mask ? apply_default_acl_nftw_x : apply_default_acl_nftw;
+
+ int nftw_result = nftw(target, fn, max_levels, flags);
if (nftw_result == 0) {
/* Success */
}
bool recursive = false;
- /* bool no_exec_mask is declared static/global */
+ bool no_exec_mask = false;
struct option long_options[] = {
/* These options set a flag. */
const char* target = argv[arg_index];
bool reapp_result = false;
+ /* Make sure we can access the given path before we go out of our
+ * way to please it. Doing this check outside of
+ * apply_default_acl() lets us spit out a better error message for
+ * typos, too.
+ */
+ if (!path_accessible(target)) {
+ fprintf(stderr, "%s: %s: No such file or directory\n", argv[0], target);
+ result = EXIT_FAILURE;
+ continue;
+ }
+
if (recursive) {
- reapp_result = apply_default_acl_recursive(target);
+ reapp_result = apply_default_acl_recursive(target, no_exec_mask);
}
else {
- /* It's either normal file, or we're not operating recursively. */
- reapp_result = apply_default_acl(target);
+ /* It's either a normal file, or we're not operating recursively. */
+ reapp_result = apply_default_acl(target, no_exec_mask);
}
if (!reapp_result) {
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