Commit 473a3211 authored by Peter Maydell's avatar Peter Maydell
Browse files

Merge remote-tracking branch 'remotes/gkurz/tags/for-upstream' into staging 



Just a single fix for an annoying regression introduced in 2.9 when fixing
CVE-2016-9602.

# gpg: Signature made Thu 10 Aug 2017 13:40:28 BST
# gpg:                using DSA key 0x02FC3AEB0101DBC2
# gpg: Good signature from "Greg Kurz <groug@kaod.org>"
# gpg:                 aka "Greg Kurz <groug@free.fr>"
# gpg:                 aka "Greg Kurz <gkurz@linux.vnet.ibm.com>"
# gpg:                 aka "Gregory Kurz (Groug) <groug@free.fr>"
# gpg:                 aka "[jpeg image of size 3330]"
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: 2BD4 3B44 535E C0A7 9894  DBA2 02FC 3AEB 0101 DBC2

* remotes/gkurz/tags/for-upstream:
  9pfs: local: fix fchmodat_nofollow() limitations

Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
parents b38df311 4751fd53

hw/9pfs/9p-local.c

+35 −7
Original line number Diff line number Diff line
@@ -333,17 +333,27 @@ update_map_file: 


static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode)

{

    struct stat stbuf;

    int fd, ret;



    /* FIXME: this should be handled with fchmodat(AT_SYMLINK_NOFOLLOW).

     * Unfortunately, the linux kernel doesn't implement it yet. As an

     * alternative, let's open the file and use fchmod() instead. This

     * may fail depending on the permissions of the file, but it is the

     * best we can do to avoid TOCTTOU. We first try to open read-only

     * in case name points to a directory. If that fails, we try write-only

     * in case name doesn't point to a directory.

     * Unfortunately, the linux kernel doesn't implement it yet.

     */

    fd = openat_file(dirfd, name, O_RDONLY, 0);



     /* First, we clear non-racing symlinks out of the way. */

    if (fstatat(dirfd, name, &stbuf, AT_SYMLINK_NOFOLLOW)) {

        return -1;

    }

    if (S_ISLNK(stbuf.st_mode)) {

        errno = ELOOP;

        return -1;

    }



    /* Access modes are ignored when O_PATH is supported. We try O_RDONLY and

     * O_WRONLY for old-systems that don't support O_PATH.

     */

    fd = openat_file(dirfd, name, O_RDONLY | O_PATH_9P_UTIL, 0);

#if O_PATH_9P_UTIL == 0

    if (fd == -1) {

        /* In case the file is writable-only and isn't a directory. */

        if (errno == EACCES) {
@@ -357,6 +367,24 @@ static int fchmodat_nofollow(int dirfd, const char *name, mode_t mode) 
        return -1;

    }

    ret = fchmod(fd, mode);

#else

    if (fd == -1) {

        return -1;

    }



    /* Now we handle racing symlinks. */

    ret = fstat(fd, &stbuf);

    if (!ret) {

        if (S_ISLNK(stbuf.st_mode)) {

            errno = ELOOP;

            ret = -1;

        } else {

            char *proc_path = g_strdup_printf("/proc/self/fd/%d", fd);

            ret = chmod(proc_path, mode);

            g_free(proc_path);

        }

    }

#endif

    close_preserve_errno(fd);

    return ret;

}

hw/9pfs/9p-util.h

+15 −9
Original line number Diff line number Diff line
@@ -13,6 +13,12 @@ 
#ifndef QEMU_9P_UTIL_H

#define QEMU_9P_UTIL_H



#ifdef O_PATH

#define O_PATH_9P_UTIL O_PATH

#else

#define O_PATH_9P_UTIL 0

#endif



static inline void close_preserve_errno(int fd)

{

    int serrno = errno;
@@ -22,13 +28,8 @@ static inline void close_preserve_errno(int fd) 


static inline int openat_dir(int dirfd, const char *name)

{

#ifdef O_PATH

#define OPENAT_DIR_O_PATH O_PATH

#else

#define OPENAT_DIR_O_PATH 0

#endif

    return openat(dirfd, name,

                  O_DIRECTORY | O_RDONLY | O_NOFOLLOW | OPENAT_DIR_O_PATH);

                  O_DIRECTORY | O_RDONLY | O_NOFOLLOW | O_PATH_9P_UTIL);

}



static inline int openat_file(int dirfd, const char *name, int flags,
@@ -43,9 +44,14 @@ static inline int openat_file(int dirfd, const char *name, int flags, 
    }



    serrno = errno;

    /* O_NONBLOCK was only needed to open the file. Let's drop it. */

    /* O_NONBLOCK was only needed to open the file. Let's drop it. We don't

     * do that with O_PATH since fcntl(F_SETFL) isn't supported, and openat()

     * ignored it anyway.

     */

    if (!(flags & O_PATH_9P_UTIL)) {

        ret = fcntl(fd, F_SETFL, flags);

        assert(!ret);

    }

    errno = serrno;

    return fd;

}