From: Greg Kurz Date: Fri, 5 May 2017 14:48:08 +0200 Subject: [PATCH] 9pfs: local: forbid client access to metadata (CVE-2017-7493) When using the mapped-file security mode, we shouldn't let the client mess with the metadata. The current code already tries to hide the metadata dir from the client by skipping it in local_readdir(). But the client can still access or modify it through several other operations. This can be used to escalate privileges in the guest. Affected backend operations are: - local_mknod() - local_mkdir() - local_open2() - local_symlink() - local_link() - local_unlinkat() - local_renameat() - local_rename() - local_name_to_path() Other operations are safe because they are only passed a fid path, which is computed internally in local_name_to_path(). This patch converts all the functions listed above to fail and return EINVAL when being passed the name of the metadata dir. This may look like a poor choice for errno, but there's no such thing as an illegal path name on Linux and I could not think of anything better. This fixes CVE-2017-7493. Reported-by: Leo Gaspard Signed-off-by: Greg Kurz Reviewed-by: Eric Blake (cherry picked from commit 7a95434e0ca8a037fd8aa1a2e2461f92585eb77b) --- hw/9pfs/9p-local.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 56 insertions(+), 2 deletions(-) diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c index f3ebca4f7a..a2486566af 100644 --- a/hw/9pfs/9p-local.c +++ b/hw/9pfs/9p-local.c @@ -452,6 +452,11 @@ static off_t local_telldir(FsContext *ctx, V9fsFidOpenState *fs) return telldir(fs->dir.stream); } +static bool local_is_mapped_file_metadata(FsContext *fs_ctx, const char *name) +{ + return !strcmp(name, VIRTFS_META_DIR); +} + static struct dirent *local_readdir(FsContext *ctx, V9fsFidOpenState *fs) { struct dirent *entry; @@ -465,8 +470,8 @@ again: if (ctx->export_flags & V9FS_SM_MAPPED) { entry->d_type = DT_UNKNOWN; } else if (ctx->export_flags & V9FS_SM_MAPPED_FILE) { - if (!strcmp(entry->d_name, VIRTFS_META_DIR)) { - /* skp the meta data directory */ + if (local_is_mapped_file_metadata(ctx, entry->d_name)) { + /* skip the meta data directory */ goto again; } entry->d_type = DT_UNKNOWN; @@ -559,6 +564,12 @@ static int local_mknod(FsContext *fs_ctx, V9fsPath *dir_path, int err = -1; int dirfd; + if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(fs_ctx, name)) { + errno = EINVAL; + return -1; + } + dirfd = local_opendir_nofollow(fs_ctx, dir_path->data); if (dirfd == -1) { return -1; @@ -605,6 +616,12 @@ static int local_mkdir(FsContext *fs_ctx, V9fsPath *dir_path, int err = -1; int dirfd; + if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(fs_ctx, name)) { + errno = EINVAL; + return -1; + } + dirfd = local_opendir_nofollow(fs_ctx, dir_path->data); if (dirfd == -1) { return -1; @@ -694,6 +711,12 @@ static int local_open2(FsContext *fs_ctx, V9fsPath *dir_path, const char *name, int err = -1; int dirfd; + if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(fs_ctx, name)) { + errno = EINVAL; + return -1; + } + /* * Mark all the open to not follow symlinks */ @@ -752,6 +775,12 @@ static int local_symlink(FsContext *fs_ctx, const char *oldpath, int err = -1; int dirfd; + if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(fs_ctx, name)) { + errno = EINVAL; + return -1; + } + dirfd = local_opendir_nofollow(fs_ctx, dir_path->data); if (dirfd == -1) { return -1; @@ -826,6 +855,12 @@ static int local_link(FsContext *ctx, V9fsPath *oldpath, int ret = -1; int odirfd, ndirfd; + if (ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(ctx, name)) { + errno = EINVAL; + return -1; + } + odirfd = local_opendir_nofollow(ctx, odirpath); if (odirfd == -1) { goto out; @@ -1096,6 +1131,12 @@ static int local_lremovexattr(FsContext *ctx, V9fsPath *fs_path, static int local_name_to_path(FsContext *ctx, V9fsPath *dir_path, const char *name, V9fsPath *target) { + if (ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(ctx, name)) { + errno = EINVAL; + return -1; + } + if (dir_path) { v9fs_path_sprintf(target, "%s/%s", dir_path->data, name); } else if (strcmp(name, "/")) { @@ -1116,6 +1157,13 @@ static int local_renameat(FsContext *ctx, V9fsPath *olddir, int ret; int odirfd, ndirfd; + if (ctx->export_flags & V9FS_SM_MAPPED_FILE && + (local_is_mapped_file_metadata(ctx, old_name) || + local_is_mapped_file_metadata(ctx, new_name))) { + errno = EINVAL; + return -1; + } + odirfd = local_opendir_nofollow(ctx, olddir->data); if (odirfd == -1) { return -1; @@ -1206,6 +1254,12 @@ static int local_unlinkat(FsContext *ctx, V9fsPath *dir, int ret; int dirfd; + if (ctx->export_flags & V9FS_SM_MAPPED_FILE && + local_is_mapped_file_metadata(ctx, name)) { + errno = EINVAL; + return -1; + } + dirfd = local_opendir_nofollow(ctx, dir->data); if (dirfd == -1) { return -1;