Commit 72f0d0bf authored by Greg Kurz's avatar Greg Kurz
Browse files

9pfs: local: lremovexattr: don't follow symlinks 



The local_lremovexattr() callback is vulnerable to symlink attacks because
it calls lremovexattr() which follows symbolic links in all path elements
but the rightmost one.

This patch introduces a helper to emulate the non-existing fremovexattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to lremovexattr().

local_lremovexattr() is converted to use this helper and opendir_nofollow().

This partly fixes CVE-2016-9602.

Signed-off-by: default avatarGreg Kurz <groug@kaod.org>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 3e36aba7

hw/9pfs/9p-posix-acl.c

+2 −8
Original line number Diff line number Diff line
@@ -58,10 +58,8 @@ static int mp_pacl_removexattr(FsContext *ctx, 
                               const char *path, const char *name)

{

    int ret;

    char *buffer;



    buffer = rpath(ctx, path);

    ret  = lremovexattr(buffer, MAP_ACL_ACCESS);

    ret = local_removexattr_nofollow(ctx, path, MAP_ACL_ACCESS);

    if (ret == -1 && errno == ENODATA) {

        /*

         * We don't get ENODATA error when trying to remove a
@@ -71,7 +69,6 @@ static int mp_pacl_removexattr(FsContext *ctx, 
        errno = 0;

        ret = 0;

    }

    g_free(buffer);

    return ret;

}
@@ -111,10 +108,8 @@ static int mp_dacl_removexattr(FsContext *ctx, 
                               const char *path, const char *name)

{

    int ret;

    char *buffer;



    buffer = rpath(ctx, path);

    ret  = lremovexattr(buffer, MAP_ACL_DEFAULT);

    ret = local_removexattr_nofollow(ctx, path, MAP_ACL_DEFAULT);

    if (ret == -1 && errno == ENODATA) {

        /*

         * We don't get ENODATA error when trying to remove a
@@ -124,7 +119,6 @@ static int mp_dacl_removexattr(FsContext *ctx, 
        errno = 0;

        ret = 0;

    }

    g_free(buffer);

    return ret;

}

hw/9pfs/9p-xattr-user.c

+1 −7
Original line number Diff line number Diff line
@@ -81,9 +81,6 @@ static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name, 
static int mp_user_removexattr(FsContext *ctx,

                               const char *path, const char *name)

{

    char *buffer;

    int ret;



    if (strncmp(name, "user.virtfs.", 12) == 0) {

        /*

         * Don't allow fetch of user.virtfs namesapce
@@ -92,10 +89,7 @@ static int mp_user_removexattr(FsContext *ctx, 
        errno = EACCES;

        return -1;

    }

    buffer = rpath(ctx, path);

    ret = lremovexattr(buffer, name);

    g_free(buffer);

    return ret;

    return local_removexattr_nofollow(ctx, path, name);

}



XattrOperations mapped_user_xattr = {

hw/9pfs/9p-xattr.c

+31 −5
Original line number Diff line number Diff line
@@ -234,17 +234,43 @@ int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value, 
    return local_setxattr_nofollow(ctx, path, name, value, size, flags);

}



int pt_removexattr(FsContext *ctx, const char *path, const char *name)

static ssize_t fremovexattrat_nofollow(int dirfd, const char *filename,

                                       const char *name)

{

    char *buffer;

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

    int ret;



    buffer = rpath(ctx, path);

    ret = lremovexattr(path, name);

    g_free(buffer);

    ret = lremovexattr(proc_path, name);

    g_free(proc_path);

    return ret;

}



ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path,

                                   const char *name)

{

    char *dirpath = g_path_get_dirname(path);

    char *filename = g_path_get_basename(path);

    int dirfd;

    ssize_t ret = -1;



    dirfd = local_opendir_nofollow(ctx, dirpath);

    if (dirfd == -1) {

        goto out;

    }



    ret = fremovexattrat_nofollow(dirfd, filename, name);

    close_preserve_errno(dirfd);

out:

    g_free(dirpath);

    g_free(filename);

    return ret;

}



int pt_removexattr(FsContext *ctx, const char *path, const char *name)

{

    return local_removexattr_nofollow(ctx, path, name);

}



ssize_t notsup_getxattr(FsContext *ctx, const char *path, const char *name,

                        void *value, size_t size)

{

hw/9pfs/9p-xattr.h

+2 −0
Original line number Diff line number Diff line
@@ -34,6 +34,8 @@ ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path, 
ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,

                                const char *name, void *value, size_t size,

                                int flags);

ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path,

                                   const char *name);



extern XattrOperations mapped_user_xattr;

extern XattrOperations passthrough_user_xattr;