Commit 9fd2ecdc authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Aneesh Kumar K.V
Browse files

virtfs-proxy-helper: use setresuid and setresgid 



The setfsuid and setfsgid system calls are obscure and they complicate
the error checking (that glibc's warn_unused_result "feature" forces
us to do).  Switch to the standard setresuid and setresgid functions.

Signed-off-by: default avatarPaolo Bonzini <pbonini@redhat.com>
Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
parent 16c6c80a

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;