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Fix small mount propagation bug.

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The MS_PRIVATE flag was not being cleared in addPeer.

Reported-by: syzbot+ea0d65b2da47bf96a8d1@syzkaller.appspotmail.com
PiperOrigin-RevId: 557949154
This commit is contained in:
Lucas Manning
2023-08-17 15:14:15 -07:00
committed by gVisor bot
parent 5ba2eb884a
commit 960b564a68
4 changed files with 45 additions and 38 deletions
Download Patch File Download Diff File Expand all files Collapse all files
pkg/sentry/vfs/mount.go
+16 -24
View File
@@ -87,8 +87,8 @@ type Mount struct {
// Mount. children is protected by VirtualFilesystem.mountMu.
children map[*Mount]struct{}
// propFlags are the propagation flags set on this mount.
propFlags uint32
// isShared indicates this mount has the MS_SHARED propagation type.
isShared bool
// sharedEntry represents an entry in a circular list (ring) of mounts in a
// shared peer group.
@@ -116,14 +116,14 @@ func (sharedMapper) linkerFor(mnt *Mount) *sharedEntry { return &mnt.sharedEntry
func newMount(vfs *VirtualFilesystem, fs *Filesystem, root *Dentry, mntns *MountNamespace, opts *MountOptions) *Mount {
mnt := &Mount{
ID: vfs.lastMountID.Add(1),
Flags: opts.Flags,
vfs: vfs,
fs: fs,
root: root,
ns: mntns,
propFlags: linux.MS_PRIVATE,
refs: atomicbitops.FromInt64(1),
ID: vfs.lastMountID.Add(1),
Flags: opts.Flags,
vfs: vfs,
fs: fs,
root: root,
ns: mntns,
isShared: false,
refs: atomicbitops.FromInt64(1),
}
if opts.ReadOnly {
mnt.setReadOnlyLocked(true)
@@ -148,20 +148,12 @@ func (mnt *Mount) generateOptionalTags() string {
defer mnt.vfs.mountMu.Unlock()
// TODO(b/249777195): Support MS_SLAVE and MS_UNBINDABLE propagation types.
var optional string
if mnt.shared() {
if mnt.isShared {
optional = fmt.Sprintf("shared:%d", mnt.groupID)
}
return optional
}
func (mnt *Mount) shared() bool {
return mnt.propFlags&linux.MS_SHARED != 0
}
func (mnt *Mount) private() bool {
return mnt.propFlags&linux.MS_PRIVATE != 0
}
// NewFilesystem creates a new filesystem object not yet associated with any
// mounts. It can be installed into the filesystem tree with ConnectMountAt.
// Note that only the filesystem-specific mount options from opts are used by
@@ -319,7 +311,7 @@ func (vfs *VirtualFilesystem) cloneMount(mnt *Mount, root *Dentry, mopts *MountO
}
}
clone := vfs.NewDisconnectedMount(mnt.fs, root, opts)
if mnt.shared() {
if mnt.isShared {
vfs.addPeer(mnt, clone)
}
return clone
@@ -443,7 +435,7 @@ func (vfs *VirtualFilesystem) UmountAt(ctx context.Context, creds *auth.Credenti
umountTree := []*Mount{vd.mount}
parent, mountpoint := vd.mount.parent(), vd.mount.point()
if parent != nil && parent.shared() {
if parent != nil && parent.isShared {
for peer := parent.sharedEntry.Next(); peer != parent; peer = peer.sharedEntry.Next() {
umountMnt := vfs.mounts.Lookup(peer, mountpoint)
// From https://www.kernel.org/doc/Documentation/filesystems/sharedsubtree.txt:
@@ -537,7 +529,7 @@ func (vfs *VirtualFilesystem) umountRecursiveLocked(mnt *Mount, opts *umountRecu
if parent := mnt.parent(); parent != nil && (opts.disconnectHierarchy || !parent.umounted) {
vdsToDecRef = append(vdsToDecRef, vfs.disconnectLocked(mnt))
}
if mnt.shared() {
if mnt.isShared {
vfs.setPropagation(mnt, linux.MS_PRIVATE)
}
}
@@ -885,12 +877,12 @@ retry:
// Either the mount point at new_root, or the parent mount of that mount
// point, has propagation type MS_SHARED.
if newRootParent := newRootVd.mount.parent(); newRootVd.mount.shared() || newRootParent.shared() {
if newRootParent := newRootVd.mount.parent(); newRootVd.mount.isShared || newRootParent.isShared {
vfs.mountMu.Unlock()
return linuxerr.EINVAL
}
// put_old is a mount point and has the propagation type MS_SHARED.
if putOldVd.mount.root == putOldVd.dentry && putOldVd.mount.shared() {
if putOldVd.mount.root == putOldVd.dentry && putOldVd.mount.isShared {
vfs.mountMu.Unlock()
return linuxerr.EINVAL
}
pkg/sentry/vfs/namespace.go
+1 -1
View File
@@ -179,7 +179,7 @@ func (vfs *VirtualFilesystem) CloneMountNamespace(
ns.root.root.IncRef()
ns.root.fs.IncRef()
newns.root = newMount(vfs, ns.root.fs, ns.root.root, newns, &MountOptions{Flags: ns.root.Flags, ReadOnly: ns.root.ReadOnly()})
if ns.root.shared() {
if ns.root.isShared {
vfs.addPeer(ns.root, newns.root)
}
vfs.updateRootAndCWD(ctx, root, cwd, ns.root, newns.root)
pkg/sentry/vfs/propagation.go
+11 -13
View File
@@ -56,26 +56,27 @@ func propTypeToString(pflag uint32) string {
func (vfs *VirtualFilesystem) setPropagation(mnt *Mount, pflag uint32) error {
switch pflag {
case linux.MS_SHARED:
if mnt.private() {
if !mnt.isShared {
id, err := vfs.allocateGroupID()
if err != nil {
return err
}
mnt.groupID = id
sharedRingInit(mnt)
mnt.isShared = true
}
case linux.MS_PRIVATE:
if mnt.shared() {
if mnt.isShared {
if sharedRingEmpty(mnt) {
vfs.freeGroupID(mnt.groupID)
}
sharedRingRemove(mnt)
mnt.groupID = 0
mnt.isShared = false
}
default:
panic(fmt.Sprintf("unsupported propagation type: %s", propTypeToString(pflag)))
}
mnt.propFlags = pflag
return nil
}
@@ -84,9 +85,8 @@ func (vfs *VirtualFilesystem) setPropagation(mnt *Mount, pflag uint32) error {
//
// +checklocks:vfs.mountMu
func (vfs *VirtualFilesystem) addPeer(mnt *Mount, new *Mount) {
mnt.propFlags |= linux.MS_SHARED
sharedRingAdd(mnt, new)
new.propFlags |= linux.MS_SHARED
new.isShared = true
new.groupID = mnt.groupID
}
@@ -99,10 +99,10 @@ func (vfs *VirtualFilesystem) addPeer(mnt *Mount, new *Mount) {
// +checklocksalias:mnt.vfs.mountMu=vfs.mountMu
func (vfs *VirtualFilesystem) preparePropagationTree(mnt *Mount, vd VirtualDentry) map[*Mount]VirtualDentry {
tree := map[*Mount]VirtualDentry{}
if !vd.mount.shared() {
if !vd.mount.isShared {
return tree
}
if !mnt.shared() {
if !mnt.isShared {
vfs.setPropagation(mnt, linux.MS_SHARED)
}
for peer := vd.mount.sharedEntry.Next(); peer != vd.mount; peer = peer.sharedEntry.Next() {
@@ -184,11 +184,9 @@ func (vfs *VirtualFilesystem) SetMountPropagationAt(ctx context.Context, creds *
func (vfs *VirtualFilesystem) SetMountPropagation(mnt *Mount, propFlags uint32) {
vfs.mountMu.Lock()
defer vfs.mountMu.Unlock()
if propFlags != mnt.propFlags {
if propFlags&(linux.MS_SHARED|linux.MS_PRIVATE) != 0 {
vfs.setPropagation(mnt, propFlags)
} else {
panic(fmt.Sprintf("unsupported propagation type: %s", propTypeToString(propFlags)))
}
if propFlags&(linux.MS_SHARED|linux.MS_PRIVATE) != 0 {
vfs.setPropagation(mnt, propFlags)
} else {
panic(fmt.Sprintf("unsupported propagation type: %s", propTypeToString(propFlags)))
}
}
test/syscalls/linux/mount.cc
+17
View File
@@ -49,6 +49,7 @@
#include "test/util/capability_util.h"
#include "test/util/file_descriptor.h"
#include "test/util/fs_util.h"
#include "test/util/linux_capability_util.h"
#include "test/util/mount_util.h"
#include "test/util/multiprocess_util.h"
#include "test/util/posix_error.h"
@@ -1443,6 +1444,22 @@ TEST(MountTest, DeadMountsAreDecRefd) {
}
}
TEST(MountTest, UmountSharedBind) {
SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));
std::string home = NewTempAbsPath();
ASSERT_NO_ERRNO(Mkdir(home));
ASSERT_THAT(chdir(home.c_str()), SyscallSucceeds());
constexpr char dirpath[] = "./file";
ASSERT_THAT(mkdir(dirpath, 0), SyscallSucceeds());
ASSERT_THAT(mount(dirpath, dirpath, 0, MS_BIND, 0), SyscallSucceeds());
ASSERT_THAT(mount(0, dirpath, 0, MS_SHARED, 0), SyscallSucceeds());
ASSERT_THAT(mount(dirpath, dirpath, 0, MS_BIND, 0), SyscallSucceeds());
ASSERT_THAT(mount(0, dirpath, 0, MS_SHARED, 0), SyscallSucceeds());
ASSERT_THAT(umount2(dirpath, MNT_DETACH), SyscallSucceeds());
ASSERT_THAT(umount2(dirpath, MNT_DETACH), SyscallSucceeds());
}
TEST(MountTest, MountNamespace) {
SKIP_IF(!ASSERT_NO_ERRNO_AND_VALUE(HaveCapability(CAP_SYS_ADMIN)));