X-Git-Url: https://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=src%2Fapply-default-acl.c;h=d97d67d25fed90d5b053652f2dcf2cb39867ea10;hb=8a38e0e6e0d8a4247933dd11812062c3590451dd;hp=5fea3a30a6efcb9c7359d5f9a19d25de7ead83e5;hpb=012ac3813d30a1bc3f405a2f8f33809cea607c6c;p=apply-default-acl.git diff --git a/src/apply-default-acl.c b/src/apply-default-acl.c index 5fea3a3..d97d67d 100644 --- a/src/apply-default-acl.c +++ b/src/apply-default-acl.c @@ -10,10 +10,10 @@ #define _GNU_SOURCE #include +#include /* AT_FOO constants */ #include /* nftw() et al. */ #include -#include /* dirname() */ -#include /* PATH_MAX */ +#include /* basename(), dirname() */ #include #include #include @@ -35,28 +35,29 @@ /** - * @brief Get the mode bits from the given path. + * @brief Get the mode bits from the given file descriptor. * - * @param path - * The path (file or directory) whose mode we want. + * @param fd + * The file descriptor (which may reference a directory) whose + * mode we want. * * @return A mode_t (st_mode) structure containing the mode bits. * See sys/stat.h for details. */ -mode_t get_mode(const char* path) { - if (path == NULL) { +mode_t get_mode(int fd) { + if (fd <= 0) { errno = ENOENT; - return -1; + return ACL_ERROR; } struct stat s; - int result = stat(path, &s); + int result = fstat(fd, &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; } } @@ -64,22 +65,85 @@ mode_t get_mode(const char* path) { /** - * @brief Determine whether or not the given path is a regular file. + * @brief Determine if the given file descriptor might refer to an + * (unsafe) hard link. + * + * @param fd + * The file descriptor whose link count we want to investigate. + * + * @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. + */ +bool is_hardlink_safe(int fd) { + if (fd <= 0) { + return false; + } + struct stat s; + int result = fstat(fd, &s); + if (result == 0) { + return (s.st_nlink == 1 || S_ISDIR(s.st_mode)); + } + else { + return false; + } +} + + +/** + * @brief Determine whether or not the given file descriptor is for + * a regular file. + * + * @param fd + * The file descriptor to test for regular-fileness. + * + * @return true if @c fd describes a regular file, and false otherwise. + */ +bool is_regular_file(int fd) { + if (fd <= 0) { + return false; + } + + struct stat s; + int result = fstat(fd, &s); + if (result == 0) { + return S_ISREG(s.st_mode); + } + else { + return false; + } +} + + + +/** + * @brief Determine whether or not the given path is accessible. * * @param path * The path to test. * - * @return true if @c path is a regular file, false otherwise. + * @return true if @c path is accessible to the current effective + * user/group, false otherwise. */ -bool is_regular_file(const char* path) { +bool path_accessible(const char* path) { if (path == NULL) { return false; } - struct stat s; - int result = stat(path, &s); + /* 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 S_ISREG(s.st_mode); + return true; } else { return false; @@ -96,13 +160,38 @@ bool is_regular_file(const char* path) { * * @return true if @c path is a directory, false otherwise. */ -bool is_directory(const char* path) { +bool is_path_directory(const char* path) { if (path == NULL) { return false; } struct stat s; - int result = stat(path, &s); + int result = lstat(path, &s); + if (result == 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; + int result = fstat(fd, &s); if (result == 0) { return S_ISDIR(s.st_mode); } @@ -207,7 +296,13 @@ int acl_set_entry(acl_t* aclp, ACL. */ acl_entry_t new_entry; - /* We allocate memory here that we should release! */ + /* The acl_create_entry() function can allocate new memory and/or + * change the location of the ACL structure entirely. When that + * happens, the value pointed to by aclp is updated, which means + * that a new acl_t gets "passed out" to our caller, eventually to + * be fed to acl_free(). In other words, we should still be freeing + * the right thing, even if the value pointed to by aclp changes. + */ int c_result = acl_create_entry(aclp, &new_entry); if (c_result == ACL_ERROR) { perror("acl_set_entry (acl_create_entry)"); @@ -250,20 +345,20 @@ int acl_set_entry(acl_t* aclp, * @brief Determine the number of entries in the given ACL. * * @param acl - * A pointer to an @c acl_t structure. + * The ACL to inspect. * * @return Either the non-negative number of entries in @c acl, or * @c ACL_ERROR on error. */ -int acl_entry_count(acl_t* acl) { +int acl_entry_count(acl_t acl) { acl_entry_t entry; int entry_count = 0; - int result = acl_get_entry(*acl, ACL_FIRST_ENTRY, &entry); + int result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry); while (result == ACL_SUCCESS) { entry_count++; - result = acl_get_entry(*acl, ACL_NEXT_ENTRY, &entry); + result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry); } if (result == ACL_ERROR) { @@ -282,14 +377,14 @@ int acl_entry_count(acl_t* acl) { * An ACL is minimal if it has fewer than four entries. * * @param acl - * A pointer to an acl_t structure. + * The ACL whose minimality is in question. * * @return * - @c ACL_SUCCESS - @c acl is minimal * - @c ACL_FAILURE - @c acl is not minimal * - @c ACL_ERROR - Unexpected library error */ -int acl_is_minimal(acl_t* acl) { +int acl_is_minimal(acl_t acl) { int ec = acl_entry_count(acl); @@ -309,29 +404,17 @@ int acl_is_minimal(acl_t* acl) { /** - * @brief Determine whether the given path has an ACL whose mask - * denies execute. + * @brief Determine whether the given ACL's mask denies execute. * - * @param path - * The path to check. + * @param acl + * The ACL whose mask we want to check. * * @return - * - @c ACL_SUCCESS - @c path has a mask which denies execute. - * - @c ACL_FAILURE - The ACL for @c path does not deny execute, - * or @c path has no extended ACL at all. + * - @c ACL_SUCCESS - The @c acl has a mask which denies execute. + * - @c ACL_FAILURE - The @c acl has a mask which does not deny execute. * - @c ACL_ERROR - Unexpected library error. */ -int acl_execute_masked(const char* path) { - - acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS); - - if (acl == (acl_t)NULL) { - perror("acl_execute_masked (acl_get_file)"); - return ACL_ERROR; - } - - /* Our return value. */ - int result = ACL_FAILURE; +int acl_execute_masked(acl_t acl) { acl_entry_t entry; int ge_result = acl_get_entry(acl, ACL_FIRST_ENTRY, &entry); @@ -342,8 +425,7 @@ int acl_execute_masked(const char* path) { if (tag_result == ACL_ERROR) { perror("acl_execute_masked (acl_get_tag_type)"); - result = ACL_ERROR; - goto cleanup; + return ACL_ERROR; } if (tag == ACL_MASK) { @@ -354,15 +436,13 @@ int acl_execute_masked(const char* path) { int ps_result = acl_get_permset(entry, &permset); if (ps_result == ACL_ERROR) { perror("acl_execute_masked (acl_get_permset)"); - result = ACL_ERROR; - goto cleanup; + return ACL_ERROR; } int gp_result = acl_get_perm(permset, ACL_EXECUTE); if (gp_result == ACL_ERROR) { perror("acl_execute_masked (acl_get_perm)"); - result = ACL_ERROR; - goto cleanup; + return ACL_ERROR; } if (gp_result == ACL_FAILURE) { @@ -374,42 +454,41 @@ int acl_execute_masked(const char* path) { ge_result = acl_get_entry(acl, ACL_NEXT_ENTRY, &entry); } - cleanup: - acl_free(acl); - return result; + return ACL_FAILURE; } + /** - * @brief Determine whether @c path is executable (by anyone) or a + * @brief Determine whether @c fd is executable (by anyone) or a * directory. * * 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 path - * is a directory, the answer is a clear-cut yes. This behavior is - * modeled after the capital 'X' perms of setfacl. + * 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 path is a file, we check the @a effective permissions, + * If @c fd describes a file, we check the @a effective permissions, * contrary to what setfacl does. * - * @param path - * The path to check. + * @param fd + * The file descriptor to check. * * @return - * - @c ACL_SUCCESS - @c path is a directory, or someone has effective + * - @c ACL_SUCCESS - @c fd describes a directory, or someone has effective execute permissions. - * - @c ACL_FAILURE - @c path is a regular file and nobody can execute + * - @c ACL_FAILURE - @c fd describes a regular file and nobody can execute it. * - @c ACL_ERROR - Unexpected library error. */ -int any_can_execute_or_dir(const char* path) { +int any_can_execute_or_dir(int fd) { - if (is_directory(path)) { + if (is_directory(fd)) { /* That was easy... */ return ACL_SUCCESS; } - acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS); + acl_t acl = acl_get_fd(fd); if (acl == (acl_t)NULL) { perror("any_can_execute_or_dir (acl_get_file)"); @@ -419,8 +498,8 @@ int any_can_execute_or_dir(const char* path) { /* Our return value. */ int result = ACL_FAILURE; - if (acl_is_minimal(&acl)) { - mode_t mode = get_mode(path); + if (acl_is_minimal(acl)) { + mode_t mode = get_mode(fd); if (mode & (S_IXUSR | S_IXOTH | S_IXGRP)) { result = ACL_SUCCESS; goto cleanup; @@ -435,6 +514,23 @@ int any_can_execute_or_dir(const char* path) { 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); @@ -452,8 +548,8 @@ int any_can_execute_or_dir(const char* path) { } if (gp_result == ACL_SUCCESS) { - /* Only return one if this execute bit is not masked. */ - if (acl_execute_masked(path) != ACL_SUCCESS) { + /* Only return ACL_SUCCESS if this execute bit is not masked. */ + if (acl_execute_masked(acl) != ACL_SUCCESS) { result = ACL_SUCCESS; goto cleanup; } @@ -476,59 +572,49 @@ int any_can_execute_or_dir(const char* path) { /** - * @brief Inherit the default ACL from @c parent to @c path. - * - * The @c parent parameter does not necessarily need to be the parent - * of @c path, although that will usually be the case. This overwrites - * any existing default ACL on @c path. + * @brief Set @c acl as the default ACL on @c path if it's a directory. * - * @param parent - * The parent directory whose ACL we want to inherit. + * 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. * * @param path - * The target directory whose ACL we wish to overwrite (or create). + * The target directory whose ACL we wish to replace or create. + * + * @param acl + * The ACL to set as default on @c path. * * @return - * - @c ACL_SUCCESS - The default ACL was inherited successfully. - * - @c ACL_FAILURE - Either @c parent or @c path is not a directory. + * - @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 inherit_default_acl(const char* path, const char* parent) { - - /* Our return value. */ - int result = ACL_SUCCESS; +int assign_default_acl(const char* path, acl_t acl) { if (path == NULL) { errno = ENOENT; return ACL_ERROR; } - if (!is_directory(path) || !is_directory(parent)) { + if (!is_path_directory(path)) { return ACL_FAILURE; } - acl_t parent_acl = acl_get_file(parent, ACL_TYPE_DEFAULT); - if (parent_acl == (acl_t)NULL) { - perror("inherit_default_acl (acl_get_file)"); - return ACL_ERROR; - } - - acl_t path_acl = acl_dup(parent_acl); + /* Our return value; success unless something bad happens. */ + int result = ACL_SUCCESS; + acl_t path_acl = acl_dup(acl); if (path_acl == (acl_t)NULL) { - perror("inherit_default_acl (acl_dup)"); - acl_free(parent_acl); - return ACL_ERROR; + perror("assign_default_acl (acl_dup)"); + return ACL_ERROR; /* Nothing to clean up in this case. */ } int sf_result = acl_set_file(path, ACL_TYPE_DEFAULT, path_acl); - if (sf_result == -1) { - perror("inherit_default_acl (acl_set_file)"); + if (sf_result == ACL_ERROR) { + perror("assign_default_acl (acl_set_file)"); result = ACL_ERROR; - goto cleanup; } - cleanup: acl_free(path_acl); return result; } @@ -537,26 +623,26 @@ int inherit_default_acl(const char* path, const char* parent) { /** * @brief Remove @c ACL_USER, @c ACL_GROUP, and @c ACL_MASK entries - * from the given path. + * from the given file descriptor. * - * @param path - * The path whose ACLs we want to wipe. + * @param fd + * The file descriptor whose ACLs we want to wipe. * * @return * - @c ACL_SUCCESS - The ACLs were wiped successfully, or none * existed in the first place. * - @c ACL_ERROR - Unexpected library error. */ -int wipe_acls(const char* path) { +int wipe_acls(int fd) { - if (path == NULL) { + if (fd <= 0) { errno = ENOENT; return ACL_ERROR; } - acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS); + acl_t acl = acl_get_fd(fd); if (acl == (acl_t)NULL) { - perror("wipe_acls (acl_get_file)"); + perror("wipe_acls (acl_get_fd)"); return ACL_ERROR; } @@ -585,9 +671,9 @@ int wipe_acls(const char* path) { goto cleanup; } - int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl); + int sf_result = acl_set_fd(fd, acl); if (sf_result == ACL_ERROR) { - perror("wipe_acls (acl_set_file)"); + perror("wipe_acls (acl_set_fd)"); result = ACL_ERROR; goto cleanup; } @@ -623,19 +709,59 @@ int apply_default_acl(const char* path, bool no_exec_mask) { return ACL_ERROR; } - if (!is_regular_file(path) && !is_directory(path)) { - return ACL_FAILURE; - } + /* Define these next three variables here because we may have to + * jump to the cleanup routine which expects them to exist. + */ + + /* Our return value. */ + int result = ACL_SUCCESS; + + /* The default ACL on path's parent directory */ + acl_t defacl = (acl_t)NULL; - /* dirname mangles its argument */ - char path_copy[PATH_MAX]; - strncpy(path_copy, path, PATH_MAX-1); - path_copy[PATH_MAX-1] = 0; + /* 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. + */ + char* path_copy = strdup(path); + if (path_copy == NULL) { + perror("apply_default_acl (strdup)"); + return ACL_ERROR; + } char* parent = dirname(path_copy); - if (!is_directory(parent)) { - /* Make sure dirname() did what we think it did. */ - return ACL_FAILURE; + + fd = open(path, O_NOFOLLOW); + if (fd == -1) { + if (errno == ELOOP) { + result = ACL_FAILURE; /* hit a symlink */ + goto cleanup; + } + else { + perror("apply_default_acl (open fd)"); + result = ACL_ERROR; + goto cleanup; + } + } + + + /* 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. There is TOCTOU + * 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. + */ + if (!is_hardlink_safe(fd)) { + result = ACL_FAILURE; + goto cleanup; + } + + if (!is_regular_file(fd) && !is_directory(fd)) { + result = ACL_FAILURE; + goto cleanup; } /* Default to not masking the exec bit; i.e. applying the default @@ -644,27 +770,26 @@ int apply_default_acl(const char* path, bool no_exec_mask) { bool allow_exec = true; if (!no_exec_mask) { - int ace_result = any_can_execute_or_dir(path); + int ace_result = any_can_execute_or_dir(fd); if (ace_result == ACL_ERROR) { perror("apply_default_acl (any_can_execute_or_dir)"); - return ACL_ERROR; + result = ACL_ERROR; + goto cleanup; } allow_exec = (bool)ace_result; } - acl_t defacl = acl_get_file(parent, ACL_TYPE_DEFAULT); + defacl = acl_get_file(parent, ACL_TYPE_DEFAULT); if (defacl == (acl_t)NULL) { perror("apply_default_acl (acl_get_file)"); - return ACL_ERROR; + result = ACL_ERROR; + goto cleanup; } - /* Our return value. */ - int result = ACL_SUCCESS; - - int wipe_result = wipe_acls(path); + int wipe_result = wipe_acls(fd); if (wipe_result == ACL_ERROR) { perror("apply_default_acl (wipe_acls)"); result = ACL_ERROR; @@ -673,16 +798,17 @@ int apply_default_acl(const char* path, bool no_exec_mask) { /* Do this after wipe_acls(), otherwise we'll overwrite the wiped ACL with this one. */ - acl_t acl = acl_get_file(path, ACL_TYPE_ACCESS); + acl_t acl = acl_get_fd(fd); if (acl == (acl_t)NULL) { - perror("apply_default_acl (acl_get_file)"); - return ACL_ERROR; + perror("apply_default_acl (acl_get_fd)"); + result = ACL_ERROR; + goto cleanup; } /* If it's a directory, inherit the parent's default. */ - int inherit_result = inherit_default_acl(path, parent); + int inherit_result = assign_default_acl(path, defacl); if (inherit_result == ACL_ERROR) { - perror("apply_default_acl (inherit_acls)"); + perror("apply_default_acl (assign_default_acl)"); result = ACL_ERROR; goto cleanup; } @@ -736,7 +862,22 @@ int apply_default_acl(const char* path, bool no_exec_mask) { } } - /* Finally, add the permset to the access ACL. */ + /* Finally, add the permset to the access ACL. It's actually + * important that we pass in the address of "acl" here, and not + * "acl" itself. Why? The call to acl_create_entry() within + * acl_set_entry() can allocate new memory for the entry. + * Sometimes that can be done in-place, in which case everything + * is cool and the new memory gets released when we call + * acl_free(acl). + * + * But occasionally, the whole ACL structure will have to be moved + * in order to allocate the extra space. When that happens, + * acl_create_entry() modifies the pointer it was passed (in this + * case, &acl) to point to the new location. We want to call + * acl_free() on the new location, and since acl_free() gets + * called right here, we need acl_create_entry() to update the + * value of "acl". To do that, it needs the address of "acl". + */ int set_result = acl_set_entry(&acl, entry); if (set_result == ACL_ERROR) { perror("apply_default_acl (acl_set_entry)"); @@ -755,15 +896,22 @@ int apply_default_acl(const char* path, bool no_exec_mask) { goto cleanup; } - int sf_result = acl_set_file(path, ACL_TYPE_ACCESS, acl); + int sf_result = acl_set_fd(fd, acl); if (sf_result == ACL_ERROR) { - perror("apply_default_acl (acl_set_file)"); + perror("apply_default_acl (acl_set_fd)"); result = ACL_ERROR; goto cleanup; } cleanup: - acl_free(defacl); + free(path_copy); + if (defacl != (acl_t)NULL) { + acl_free(defacl); + } + if (fd >= 0 && close(fd) == -1) { + perror("apply_default_acl (close)"); + result = ACL_ERROR; + } return result; } @@ -776,7 +924,7 @@ int apply_default_acl(const char* path, bool no_exec_mask) { * 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] [ [ ...]]\n\n", @@ -866,7 +1014,7 @@ int apply_default_acl_nftw_x(const char *target, */ bool apply_default_acl_recursive(const char *target, bool no_exec_mask) { - if (!is_directory(target)) { + if (!is_path_directory(target)) { return apply_default_acl(target, no_exec_mask); } @@ -953,11 +1101,22 @@ int main(int argc, char* argv[]) { 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, no_exec_mask); } else { - /* It's either normal file, or we're not operating recursively. */ + /* It's either a normal file, or we're not operating recursively. */ reapp_result = apply_default_acl(target, no_exec_mask); }