@@ -272,31 +272,76 @@ static int send_status(int sockfd, struct iovec *iovec, int status)
/*
* from man 7 capabilities, section
* Effect of User ID Changes on Capabilities:
- * 4. If the file system user ID is changed from 0 to nonzero (see setfsuid(2))
- * then the following capabilities are cleared from the effective set:
- * CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH, CAP_FOWNER, CAP_FSETID,
- * CAP_LINUX_IMMUTABLE (since Linux 2.2.30), CAP_MAC_OVERRIDE, and CAP_MKNOD
- * (since Linux 2.2.30). If the file system UID is changed from nonzero to 0,
- * then any of these capabilities that are enabled in the permitted set
- * are enabled in the effective set.
+ * If the effective user ID is changed from nonzero to 0, then the permitted
+ * set is copied to the effective set. If the effective user ID is changed
+ * from 0 to nonzero, then all capabilities are are cleared from the effective
+ * set.
+ *
+ * The setfsuid/setfsgid man pages warn that changing the effective user ID may
+ * expose the program to unwanted signals, but this is not true anymore: for an
+ * unprivileged (without CAP_KILL) program to send a signal, the real or
+ * effective user ID of the sending process must equal the real or saved user
+ * ID of the target process. Even when dropping privileges, it is enough to
+ * keep the saved UID to a "privileged" value and virtfs-proxy-helper won't
+ * be exposed to signals. So just use setresuid/setresgid.
*/
-static int setfsugid(int uid, int gid)
+static int setugid(int uid, int gid, int *suid, int *sgid)
{
+ int retval;
+
/*
- * We still need DAC_OVERRIDE because we don't change
+ * We still need DAC_OVERRIDE because we don't change
* supplementary group ids, and hence may be subjected DAC rules
*/
cap_value_t cap_list[] = {
CAP_DAC_OVERRIDE,
};
- setfsgid(gid);
- setfsuid(uid);
+ /*
+ * If suid/sgid are NULL, the saved uid/gid is set to the
+ * new effective uid/gid. If they are not, the saved uid/gid
+ * is set to the current effective user id and stored into
+ * *suid and *sgid.
+ */
+ if (!suid) {
+ suid = &uid;
+ } else {
+ *suid = geteuid();
+ }
+ if (!sgid) {
+ sgid = &gid;
+ } else {
+ *sgid = getegid();
+ }
+
+ if (setresuid(-1, uid, *suid) == -1) {
+ retval = -errno;
+ goto err_out;
+ }
+ if (setresgid(-1, gid, *sgid) == -1) {
+ retval = -errno;
+ goto err_suid;
+ }
if (uid != 0 || gid != 0) {
- return do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0);
+ if (do_cap_set(cap_list, ARRAY_SIZE(cap_list), 0) < 0) {
+ retval = -errno;
+ goto err_sgid;
+ }
}
+
return 0;
+
+err_sgid:
+ if (setresgid(-1, *sgid, *sgid) == -1) {
+ abort();
+ }
+err_suid:
+ if (setresuid(-1, *suid, *suid) == -1) {
+ abort();
+ }
+err_out:
+ return retval;
}
/*
@@ -578,17 +623,14 @@ static int do_create_others(int type, struct iovec *iovec)
v9fs_string_init(&path);
v9fs_string_init(&oldpath);
- cur_uid = geteuid();
- cur_gid = getegid();
retval = proxy_unmarshal(iovec, offset, "dd", &uid, &gid);
if (retval < 0) {
return retval;
}
offset += retval;
- retval = setfsugid(uid, gid);
+ retval = setugid(uid, gid, &cur_uid, &cur_gid);
if (retval < 0) {
- retval = -errno;
goto err_out;
}
switch (type) {
@@ -621,7 +663,7 @@ static int do_create_others(int type, struct iovec *iovec)
err_out:
v9fs_string_free(&path);
v9fs_string_free(&oldpath);
- setfsugid(cur_uid, cur_gid);
+ setugid(cur_uid, cur_gid, NULL, NULL);
return retval;
}
@@ -641,24 +683,17 @@ static int do_create(struct iovec *iovec)
if (ret < 0) {
goto unmarshal_err_out;
}
- cur_uid = geteuid();
- cur_gid = getegid();
- ret = setfsugid(uid, gid);
+ ret = setugid(uid, gid, &cur_uid, &cur_gid);
if (ret < 0) {
- /*
- * On failure reset back to the
- * old uid/gid
- */
- ret = -errno;
- goto err_out;
+ goto unmarshal_err_out;
}
ret = open(path.data, flags, mode);
if (ret < 0) {
ret = -errno;
}
-err_out:
- setfsugid(cur_uid, cur_gid);
+ setugid(cur_uid, cur_gid, NULL, NULL);
+
unmarshal_err_out:
v9fs_string_free(&path);
return ret;