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authorGreg Kurz <groug@kaod.org>2017-05-05 14:48:08 +0200
committerGreg Kurz <groug@kaod.org>2017-05-15 15:20:57 +0200
commit7a95434e0ca8a037fd8aa1a2e2461f92585eb77b (patch)
treef88df38e506ff3b387c30a71219b468fcc3a274f
parent3a8760664d5c1a1a93c9012bdb8ac07ab8fd4b0d (diff)
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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 <leo@gaspard.io> Signed-off-by: Greg Kurz <groug@kaod.org> Reviewed-by: Eric Blake <eblake@redhat.com>
-rw-r--r--hw/9pfs/9p-local.c58
1 files changed, 56 insertions, 2 deletions
diff --git a/hw/9pfs/9p-local.c b/hw/9pfs/9p-local.c
index f3ebca4..a248656 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;