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[Qemu-devel] [PULL v2 11/11] 9pfs: local: metadata file for the VirtFS r
From: |
Greg Kurz |
Subject: |
[Qemu-devel] [PULL v2 11/11] 9pfs: local: metadata file for the VirtFS root |
Date: |
Tue, 30 May 2017 15:40:40 +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>
[groug: work around a patchew false positive in
local_set_mapped_file_attrat()]
---
hw/9pfs/9p-local.c | 86 +++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 59 insertions(+), 27 deletions(-)
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index ddc5038cff39..1e78b7c9e961 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 = -1, 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 +281,26 @@ 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");
+ /* We can't go this far with map_dirfd not being a valid file
descriptor
+ * but some versions of gcc aren't smart enough to see it.
+ */
+ if (map_dirfd != -1) {
+ 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 +509,8 @@ 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 +527,7 @@ 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;
--
2.7.5
- [Qemu-devel] [PULL v2 00/11] 9pfs patches for 2.10 20170530, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 01/11] virtio-9p/xen-9p: move 9p specific bits to core 9p code, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 05/11] fsdev: fix virtfs-proxy-helper cwd, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 02/11] fsdev: don't allow unknown format in marshal/unmarshal, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 04/11] 9pfs: local: fix unlink of alien files in mapped-file mode, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 07/11] util: drop old utimensat() compat code, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 03/11] 9pfs: drop pdu_push_and_notify(), Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 06/11] 9pfs: assume utimensat() and futimens() are present, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 11/11] 9pfs: local: metadata file for the VirtFS root,
Greg Kurz <=
- [Qemu-devel] [PULL v2 10/11] 9pfs: local: simplify file opening, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 09/11] 9pfs: local: resolve special directories in paths, Greg Kurz, 2017/05/30
- [Qemu-devel] [PULL v2 08/11] 9pfs: check return value of v9fs_co_name_to_path(), Greg Kurz, 2017/05/30