Merge remote-tracking branch 'aneesh/for-upstream' into staging (16ef55ca) · Commits · SUMMER2020 / students / proj-2021291

fsdev/virtfs-proxy-helper.c

+64 −29

Original line number	Diff line number	Diff line
		@@ -272,16 +272,23 @@ 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
		* supplementary group ids, and hence may be subjected DAC rules
		@@ -290,13 +297,51 @@ static int setfsugid(int uid, int gid)
		CAP_DAC_OVERRIDE,
		};

		setfsgid(gid);
		setfsuid(uid);
		*suid = geteuid();
		*sgid = getegid();

		if (setresgid(-1, gid, *sgid) == -1) {
		retval = -errno;
		goto err_out;
		}

		if (setresuid(-1, uid, *suid) == -1) {
		retval = -errno;
		goto err_sgid;
		}

		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_suid;
		}
		}
		return 0;

		err_suid:
		if (setresuid(-1, suid, suid) == -1) {
		abort();
		}
		err_sgid:
		if (setresgid(-1, sgid, sgid) == -1) {
		abort();
		}
		err_out:
		return retval;
		}

		/*
		* This is used to reset the ugid back with the saved values
		* There is nothing much we can do checking error values here.
		*/
		static void resetugid(int suid, int sgid)
		{
		if (setresgid(-1, sgid, sgid) == -1) {
		abort();
		}
		if (setresuid(-1, suid, suid) == -1) {
		abort();
		}
		}

		/*
		@@ -578,18 +623,15 @@ 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;
		goto unmarshal_err_out;
		}
		switch (type) {
		case T_MKNOD:
		@@ -619,9 +661,10 @@ static int do_create_others(int type, struct iovec *iovec)
		}

		err_out:
		resetugid(cur_uid, cur_gid);
		unmarshal_err_out:
		v9fs_string_free(&path);
		v9fs_string_free(&oldpath);
		setfsugid(cur_uid, cur_gid);
		return retval;
		}

		@@ -641,24 +684,16 @@ 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);
		resetugid(cur_uid, cur_gid);
		unmarshal_err_out:
		v9fs_string_free(&path);
		return ret;