From 81ffbf5ab1458e357a761f1272105a55829b351e Mon Sep 17 00:00:00 2001 From: Greg Kurz Date: Thu, 25 May 2017 10:30:14 +0200 Subject: [PATCH] 9pfs: local: metadata file for the VirtFS root 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 Signed-off-by: Greg Kurz Reviewed-by: Eric Blake Tested-by: Leo Gaspard [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 ddc5038cff..1e78b7c9e9 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; + int map_dirfd = -1, map_fd; + bool is_root = !strcmp(name, "."); - 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; - } - - fp = local_fopenat(map_dirfd, name, "r"); - if (!fp) { - if (errno == ENOENT) { - goto update_map_file; - } else { - close_preserve_errno(map_dirfd); + 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; } + + 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;