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[Qemu-devel] [PULL 11/11] 9pfs: local: metadata file for the VirtFS root
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PULL 11/11] 9pfs: local: metadata file for the VirtFS root |
Date: |
Mon, 29 May 2017 11:05:40 +0200 |
When using the mapped-file security, credentials are stored in a metadata
directory located in the parent directory. This is okay for all paths with
the notable exception of the root path, since we don't want and probably
can't create a metadata directory above the virtfs directory on the host.
This patch introduces a dedicated metadata file, sitting in the virtfs root
for this purpose. It relies on the fact that the "." name necessarily refers
to the virtfs root.
As for the metadata directory, we don't want the client to see this file.
The current code only cares for readdir() but there are many other places
to fix actually. The filtering logic is hence put in a separate function.
Before:
# ls -ld
drwxr-xr-x. 3 greg greg 4096 May 5 12:49 .
# chown root.root .
chown: changing ownership of '.': Is a directory
# ls -ld
drwxr-xr-x. 3 greg greg 4096 May 5 12:49 .
After:
# ls -ld
drwxr-xr-x. 3 greg greg 4096 May 5 12:49 .
# chown root.root .
# ls -ld
drwxr-xr-x. 3 root root 4096 May 5 12:50 .
and from the host:
ls -al .virtfs_metadata_root
-rwx------. 1 greg greg 26 May 5 12:50 .virtfs_metadata_root
$ cat .virtfs_metadata_root
virtfs.uid=0
virtfs.gid=0
Reported-by: Leo Gaspard <address@hidden>
Signed-off-by: Greg Kurz <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Tested-by: Leo Gaspard <address@hidden>
---
hw/9pfs/9p-local.c | 81 ++++++++++++++++++++++++++++++++++++------------------
1 file changed, 54 insertions(+), 27 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index ddc5038cff39..6442f642d326 100644
--- a/hw/9pfs/9p-local.c
+++ b/hw/9pfs/9p-local.c
@@ -107,6 +107,7 @@ static void unlinkat_preserve_errno(int dirfd, const char
*path, int flags)
}
#define VIRTFS_META_DIR ".virtfs_metadata"
+#define VIRTFS_META_ROOT_FILE VIRTFS_META_DIR "_root"
static FILE *local_fopenat(int dirfd, const char *name, const char *mode)
{
@@ -143,13 +144,17 @@ static void local_mapped_file_attr(int dirfd, const char
*name,
char buf[ATTR_MAX];
int map_dirfd;
- map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
- if (map_dirfd == -1) {
- return;
- }
+ if (strcmp(name, ".")) {
+ map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
+ if (map_dirfd == -1) {
+ return;
+ }
- fp = local_fopenat(map_dirfd, name, "r");
- close_preserve_errno(map_dirfd);
+ fp = local_fopenat(map_dirfd, name, "r");
+ close_preserve_errno(map_dirfd);
+ } else {
+ fp = local_fopenat(dirfd, VIRTFS_META_ROOT_FILE, "r");
+ }
if (!fp) {
return;
}
@@ -227,26 +232,38 @@ static int local_set_mapped_file_attrat(int dirfd, const
char *name,
int ret;
char buf[ATTR_MAX];
int uid = -1, gid = -1, mode = -1, rdev = -1;
- int map_dirfd;
-
- ret = mkdirat(dirfd, VIRTFS_META_DIR, 0700);
- if (ret < 0 && errno != EEXIST) {
- return -1;
- }
-
- map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
- if (map_dirfd == -1) {
- return -1;
- }
+ int map_dirfd, map_fd;
+ bool is_root = !strcmp(name, ".");
+
+ if (is_root) {
+ fp = local_fopenat(dirfd, VIRTFS_META_ROOT_FILE, "r");
+ if (!fp) {
+ if (errno == ENOENT) {
+ goto update_map_file;
+ } else {
+ return -1;
+ }
+ }
+ } else {
+ ret = mkdirat(dirfd, VIRTFS_META_DIR, 0700);
+ if (ret < 0 && errno != EEXIST) {
+ return -1;
+ }
- fp = local_fopenat(map_dirfd, name, "r");
- if (!fp) {
- if (errno == ENOENT) {
- goto update_map_file;
- } else {
- close_preserve_errno(map_dirfd);
+ map_dirfd = openat_dir(dirfd, VIRTFS_META_DIR);
+ if (map_dirfd == -1) {
return -1;
}
+
+ fp = local_fopenat(map_dirfd, name, "r");
+ if (!fp) {
+ if (errno == ENOENT) {
+ goto update_map_file;
+ } else {
+ close_preserve_errno(map_dirfd);
+ return -1;
+ }
+ }
}
memset(buf, 0, ATTR_MAX);
while (fgets(buf, ATTR_MAX, fp)) {
@@ -264,12 +281,21 @@ static int local_set_mapped_file_attrat(int dirfd, const
char *name,
fclose(fp);
update_map_file:
- fp = local_fopenat(map_dirfd, name, "w");
- close_preserve_errno(map_dirfd);
+ if (is_root) {
+ fp = local_fopenat(dirfd, VIRTFS_META_ROOT_FILE, "w");
+ } else {
+ fp = local_fopenat(map_dirfd, name, "w");
+ close_preserve_errno(map_dirfd);
+ }
if (!fp) {
return -1;
}
+ map_fd = fileno(fp);
+ assert(map_fd != -1);
+ ret = fchmod(map_fd, 0600);
+ assert(ret == 0);
+
if (credp->fc_uid != -1) {
uid = credp->fc_uid;
}
@@ -478,7 +504,8 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState
*fs)
static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name)
{
- return !strcmp(name, VIRTFS_META_DIR);
+ return
+ !strcmp(name, VIRTFS_META_DIR) || !strcmp(name, VIRTFS_META_ROOT_FILE);
}
static struct dirent *local_readdir(FsContext *ctx, V9fsFidOpenState *fs)
@@ -495,7 +522,7 @@ again:
entry->d_type = DT_UNKNOWN;
} else if (ctx->export_flags & V9FS_SM_MAPPED_FILE) {
if (local_is_mapped_file_metadata(ctx, entry->d_name)) {
- /* skip the meta data directory */
+ /* skip the meta data */
goto again;
}
entry->d_type = DT_UNKNOWN;
--
2.7.4
- [Qemu-devel] [PULL 01/11] virtio-9p/xen-9p: move 9p specific bits to core 9p code, (continued)
- [Qemu-devel] [PULL 01/11] virtio-9p/xen-9p: move 9p specific bits to core 9p code, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 03/11] 9pfs: drop pdu_push_and_notify(), Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 02/11] fsdev: don't allow unknown format in marshal/unmarshal, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 05/11] fsdev: fix virtfs-proxy-helper cwd, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 06/11] 9pfs: assume utimensat() and futimens() are present, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 09/11] 9pfs: local: resolve special directories in paths, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 04/11] 9pfs: local: fix unlink of alien files in mapped-file mode, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 07/11] util: drop old utimensat() compat code, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 08/11] 9pfs: check return value of v9fs_co_name_to_path(), Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 10/11] 9pfs: local: simplify file opening, Greg Kurz, 2017/05/29
- [Qemu-devel] [PULL 11/11] 9pfs: local: metadata file for the VirtFS root,
Greg Kurz <=
- Re: [Qemu-devel] [PULL 00/11] 9pfs patches for 2.10 20170525, no-reply, 2017/05/29
- Re: [Qemu-devel] [PULL 00/11] 9pfs patches for 2.10 20170525, Stefan Hajnoczi, 2017/05/30