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9pfs: local: fix unlink of alien files in mapped-file mode

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When trying to remove a file from a directory, both created in non-mapped
mode, the file remains and EBADF is returned to the guest.

This is a regression introduced by commit "df4938a6651b 9pfs: local:
unlinkat: don't follow symlinks" when fixing CVE-2016-9602. It changed the
way we unlink the metadata file from

    ret = remove("$dir/.virtfs_metadata/$name");
    if (ret < 0 && errno != ENOENT) {
         /* Error out */
    }
    /* Ignore absence of metadata */

to

    fd = openat("$dir/.virtfs_metadata")
    unlinkat(fd, "$name")
    if (ret < 0 && errno != ENOENT) {
         /* Error out */
    }
    /* Ignore absence of metadata */

If $dir was created in non-mapped mode, openat() fails with ENOENT and
we pass -1 to unlinkat(), which fails in turn with EBADF.

We just need to check the return of openat() and ignore ENOENT, in order
to restore the behaviour we had with remove().

Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
[groug: rewrote the comments as suggested by Eric]
This commit is contained in:
Greg Kurz 2017-05-25 10:30:13 +02:00
parent a17d8659c4
commit 6a87e7929f
1 changed files with 15 additions and 19 deletions
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34
hw/9pfs/9p-local.c
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@ -992,6 +992,14 @@ static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
int map_dirfd;
/* We need to remove the metadata as well:
* - the metadata directory if we're removing a directory
* - the metadata file in the parent's metadata directory
*
* If any of these are missing (ie, ENOENT) then we're probably
* trying to remove something that wasn't created in mapped-file
* mode. We just ignore the error.
*/
if (flags == AT_REMOVEDIR) {
int fd;
@ -999,32 +1007,20 @@ static int local_unlinkat_common(FsContext *ctx, int dirfd, const char *name,
if (fd == -1) {
goto err_out;
}
/*
* If directory remove .virtfs_metadata contained in the
* directory
*/
ret = unlinkat(fd, VIRTFS_META_DIR, AT_REMOVEDIR);
close_preserve_errno(fd);
if (ret < 0 && errno != ENOENT) {
/*
* We didn't had the .virtfs_metadata file. May be file created
* in non-mapped mode ?. Ignore ENOENT.
*/
goto err_out;
}
}
/*
* Now remove the name from parent directory
* .virtfs_metadata directory.
*/
map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
ret = unlinkat(map_dirfd, name, 0);
close_preserve_errno(map_dirfd);
if (ret < 0 && errno != ENOENT) {
/*
* We didn't had the .virtfs_metadata file. May be file created
* in non-mapped mode ?. Ignore ENOENT.
*/
if (map_dirfd != -1) {
ret = unlinkat(map_dirfd, name, 0);
close_preserve_errno(map_dirfd);
if (ret < 0 && errno != ENOENT) {
goto err_out;
}
} else if (errno != ENOENT) {
goto err_out;
}
}