dir_is_writable: add fallback if changing UIDs fails
The SELinux policy may not allow uid/gid changes which will break the writability checks and cause sudoedit to fail.
This commit is contained in:
Todd C. Miller
198
src/edit_open.c
198
src/edit_open.c
@@ -39,10 +39,12 @@
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#if defined(HAVE_SETRESUID) || defined(HAVE_SETREUID) || defined(HAVE_SETEUID)
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void
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switch_user(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups)
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static int
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switch_user_int(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups,
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bool nonfatal)
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{
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int serrno = errno;
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int ret = -1;
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debug_decl(switch_user, SUDO_DEBUG_EDIT);
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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@@ -51,72 +53,50 @@ switch_user(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups)
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/* When restoring root, change euid first; otherwise change it last. */
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if (euid == ROOT_UID) {
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if (seteuid(ROOT_UID) != 0)
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if (seteuid(ROOT_UID) != 0) {
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if (nonfatal)
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goto done;
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sudo_fatal("seteuid(ROOT_UID)");
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}
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}
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if (setegid(egid) != 0)
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if (setegid(egid) != 0) {
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if (nonfatal)
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goto done;
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sudo_fatal("setegid(%d)", (int)egid);
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}
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if (ngroups != -1) {
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if (sudo_setgroups(ngroups, groups) != 0)
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if (sudo_setgroups(ngroups, groups) != 0) {
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if (nonfatal)
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goto done;
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sudo_fatal("setgroups");
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}
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}
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if (euid != ROOT_UID) {
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if (seteuid(euid) != 0)
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if (seteuid(euid) != 0) {
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if (nonfatal)
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goto done;
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sudo_fatal("seteuid(%u)", (unsigned int)euid);
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}
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}
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ret = 0;
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done:
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errno = serrno;
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debug_return;
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debug_return_int(ret);
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}
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#if defined(HAVE_FACCESSAT) && defined(AT_EACCESS)
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/*
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* Returns true if the open directory fd is owned or writable by the user.
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*/
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int
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dir_is_writable(int dfd, struct sudo_cred *user_cred, struct sudo_cred *cur_cred)
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static int
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switch_user_nonfatal(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups)
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{
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struct stat sb;
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int rc;
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debug_decl(dir_is_writable, SUDO_DEBUG_EDIT);
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if (fstat(dfd, &sb) == -1)
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debug_return_int(-1);
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/* If the user owns the dir we always consider it writable. */
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if (sb.st_uid == user_cred->uid) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"user uid %u matches directory uid %u",
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(unsigned int)user_cred->uid, (unsigned int)sb.st_uid);
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debug_return_int(true);
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}
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/* Change uid/gid/groups to invoking user, usually needs root perms. */
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if (cur_cred->euid != ROOT_UID) {
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if (seteuid(ROOT_UID) != 0)
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sudo_fatal("seteuid(ROOT_UID)");
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}
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switch_user(user_cred->uid, user_cred->gid, user_cred->ngroups,
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user_cred->groups);
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/* Access checks are done using the euid/egid and group vector. */
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rc = faccessat(dfd, ".", W_OK, AT_EACCESS);
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/* Restore uid/gid/groups, may need root perms. */
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if (user_cred->uid != ROOT_UID) {
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if (seteuid(ROOT_UID) != 0)
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sudo_fatal("seteuid(ROOT_UID)");
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}
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switch_user(cur_cred->euid, cur_cred->egid, cur_cred->ngroups,
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cur_cred->groups);
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if (rc == 0)
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debug_return_int(true);
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if (errno == EACCES || errno == EROFS)
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debug_return_int(false);
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debug_return_int(-1);
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return switch_user_int(euid, egid, ngroups, groups, true);
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}
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#else
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void
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switch_user(uid_t euid, gid_t egid, int ngroups, GETGROUPS_T *groups)
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{
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(void)switch_user_int(euid, egid, ngroups, groups, false);
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}
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static bool
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group_matches(gid_t target, struct sudo_cred *cred)
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{
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@@ -140,8 +120,97 @@ group_matches(gid_t target, struct sudo_cred *cred)
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debug_return_bool(false);
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}
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static bool
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is_writable(struct sudo_cred *user_cred, struct stat *sb)
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{
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debug_decl(is_writable, SUDO_DEBUG_EDIT);
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/* Other writable? */
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if (ISSET(sb->st_mode, S_IWOTH)) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"directory is writable by other");
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debug_return_int(true);
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}
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/* Group writable? */
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if (ISSET(sb->st_mode, S_IWGRP)) {
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if (group_matches(sb->st_gid, user_cred)) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"directory is writable by one of the user's groups");
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debug_return_int(true);
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}
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}
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errno = EACCES;
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debug_return_int(false);
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}
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#if defined(HAVE_FACCESSAT) && defined(AT_EACCESS)
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/*
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* Returns true if the open directory fd is owned or writable by the user.
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* Checks whether the open directory dfd is owned or writable by the user.
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* Returns true if writable, false if not, or -1 on error.
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*/
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int
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dir_is_writable(int dfd, struct sudo_cred *user_cred, struct sudo_cred *cur_cred)
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{
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struct stat sb;
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int rc;
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debug_decl(dir_is_writable, SUDO_DEBUG_EDIT);
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if (fstat(dfd, &sb) == -1)
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debug_return_int(-1);
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/* If the user owns the dir we always consider it writable. */
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if (sb.st_uid == user_cred->uid) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"user uid %u matches directory uid %u",
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(unsigned int)user_cred->uid, (unsigned int)sb.st_uid);
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debug_return_int(true);
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}
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/* Change uid/gid/groups to invoking user, usually needs root perms. */
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if (cur_cred->euid != ROOT_UID) {
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if (seteuid(ROOT_UID) != 0) {
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sudo_debug_printf(
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SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO|SUDO_DEBUG_ERRNO,
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"seteuid(ROOT_UID)");
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goto fallback;
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}
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}
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if (switch_user_nonfatal(user_cred->uid, user_cred->gid, user_cred->ngroups,
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user_cred->groups) == -1) {
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sudo_debug_printf(
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SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO|SUDO_DEBUG_ERRNO,
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"unable to switch to user_cred");
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goto fallback;
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}
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/* Access checks are done using the euid/egid and group vector. */
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rc = faccessat(dfd, ".", W_OK, AT_EACCESS);
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/* Restore uid/gid/groups, may need root perms. */
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if (user_cred->uid != ROOT_UID) {
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if (seteuid(ROOT_UID) != 0)
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sudo_fatal("seteuid(ROOT_UID)");
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}
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switch_user(cur_cred->euid, cur_cred->egid, cur_cred->ngroups,
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cur_cred->groups);
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if (rc == 0)
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debug_return_int(true);
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if (errno == EACCES || errno == EROFS)
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debug_return_int(false);
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debug_return_int(-1);
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fallback:
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debug_return_int(is_writable(user_cred, &sb));
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}
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#endif /* HAVE_FACCESSAT && AT_EACCESS */
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#if !defined(HAVE_FACCESSAT) || !defined(AT_EACCESS)
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/*
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* Checks whether the open directory dfd is owned or writable by the user.
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* Returns true if writable, false if not, or -1 on error.
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*/
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int
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dir_is_writable(int dfd, struct sudo_cred *user_cred, struct sudo_cred *cur_cred)
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@@ -160,24 +229,7 @@ dir_is_writable(int dfd, struct sudo_cred *user_cred, struct sudo_cred *cur_cred
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debug_return_int(true);
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}
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/* Other writable? */
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if (ISSET(sb.st_mode, S_IWOTH)) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"directory is writable by other");
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debug_return_int(true);
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}
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/* Group writable? */
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if (ISSET(sb.st_mode, S_IWGRP)) {
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if (group_matches(sb.st_gid, user_cred)) {
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sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
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"directory is writable by one of the user's groups");
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debug_return_int(true);
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}
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}
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errno = EACCES;
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debug_return_int(false);
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debug_return_int(is_writable(user_cred, &sb));
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}
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#endif /* HAVE_FACCESSAT && AT_EACCESS */
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