diff options
| -rw-r--r-- | pkg/sentry/fsimpl/gofer/BUILD | 12 | ||||
| -rw-r--r-- | pkg/sentry/fsimpl/gofer/gofer.go | 36 | ||||
| -rw-r--r-- | pkg/sentry/fsimpl/gofer/gofer_test.go | 64 | ||||
| -rw-r--r-- | test/syscalls/linux/open.cc | 22 |
4 files changed, 129 insertions, 5 deletions
diff --git a/pkg/sentry/fsimpl/gofer/BUILD b/pkg/sentry/fsimpl/gofer/BUILD index d15a36709..99d1e3f8f 100644 --- a/pkg/sentry/fsimpl/gofer/BUILD +++ b/pkg/sentry/fsimpl/gofer/BUILD @@ -1,4 +1,4 @@ -load("//tools:defs.bzl", "go_library") +load("//tools:defs.bzl", "go_library", "go_test") load("//tools/go_generics:defs.bzl", "go_template_instance") licenses(["notice"]) @@ -54,3 +54,13 @@ go_library( "//pkg/usermem", ], ) + +go_test( + name = "gofer_test", + srcs = ["gofer_test.go"], + library = ":gofer", + deps = [ + "//pkg/p9", + "//pkg/sentry/contexttest", + ], +) diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go index adee8bb60..20edaf643 100644 --- a/pkg/sentry/fsimpl/gofer/gofer.go +++ b/pkg/sentry/fsimpl/gofer/gofer.go @@ -444,7 +444,8 @@ type dentry struct { // refs is the reference count. Each dentry holds a reference on its // parent, even if disowned. refs is accessed using atomic memory - // operations. + // operations. When refs reaches 0, the dentry may be added to the cache or + // destroyed. If refs==-1 the dentry has already been destroyed. refs int64 // fs is the owning filesystem. fs is immutable. @@ -860,7 +861,7 @@ func (d *dentry) IncRef() { func (d *dentry) TryIncRef() bool { for { refs := atomic.LoadInt64(&d.refs) - if refs == 0 { + if refs <= 0 { return false } if atomic.CompareAndSwapInt64(&d.refs, refs, refs+1) { @@ -883,13 +884,20 @@ func (d *dentry) DecRef() { // checkCachingLocked should be called after d's reference count becomes 0 or it // becomes disowned. // +// It may be called on a destroyed dentry. For example, +// renameMu[R]UnlockAndCheckCaching may call checkCachingLocked multiple times +// for the same dentry when the dentry is visited more than once in the same +// operation. One of the calls may destroy the dentry, so subsequent calls will +// do nothing. +// // Preconditions: d.fs.renameMu must be locked for writing. func (d *dentry) checkCachingLocked() { // Dentries with a non-zero reference count must be retained. (The only way // to obtain a reference on a dentry with zero references is via path // resolution, which requires renameMu, so if d.refs is zero then it will // remain zero while we hold renameMu for writing.) - if atomic.LoadInt64(&d.refs) != 0 { + refs := atomic.LoadInt64(&d.refs) + if refs > 0 { if d.cached { d.fs.cachedDentries.Remove(d) d.fs.cachedDentriesLen-- @@ -897,6 +905,10 @@ func (d *dentry) checkCachingLocked() { } return } + if refs == -1 { + // Dentry has already been destroyed. + return + } // Non-child dentries with zero references are no longer reachable by path // resolution and should be dropped immediately. if d.vfsd.Parent() == nil || d.vfsd.IsDisowned() { @@ -949,9 +961,22 @@ func (d *dentry) checkCachingLocked() { } } +// destroyLocked destroys the dentry. It may flushes dirty pages from cache, +// close p9 file and remove reference on parent dentry. +// // Preconditions: d.fs.renameMu must be locked for writing. d.refs == 0. d is // not a child dentry. func (d *dentry) destroyLocked() { + switch atomic.LoadInt64(&d.refs) { + case 0: + // Mark the dentry destroyed. + atomic.StoreInt64(&d.refs, -1) + case -1: + panic("dentry.destroyLocked() called on already destroyed dentry") + default: + panic("dentry.destroyLocked() called with references on the dentry") + } + ctx := context.Background() d.handleMu.Lock() if !d.handle.file.isNil() { @@ -971,7 +996,10 @@ func (d *dentry) destroyLocked() { d.handle.close(ctx) } d.handleMu.Unlock() - d.file.close(ctx) + if !d.file.isNil() { + d.file.close(ctx) + d.file = p9file{} + } // Remove d from the set of all dentries. d.fs.syncMu.Lock() delete(d.fs.dentries, d) diff --git a/pkg/sentry/fsimpl/gofer/gofer_test.go b/pkg/sentry/fsimpl/gofer/gofer_test.go new file mode 100644 index 000000000..82bc239db --- /dev/null +++ b/pkg/sentry/fsimpl/gofer/gofer_test.go @@ -0,0 +1,64 @@ +// Copyright 2020 The gVisor Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +package gofer + +import ( + "sync/atomic" + "testing" + + "gvisor.dev/gvisor/pkg/p9" + "gvisor.dev/gvisor/pkg/sentry/contexttest" +) + +func TestDestroyIdempotent(t *testing.T) { + fs := filesystem{ + dentries: make(map[*dentry]struct{}), + opts: filesystemOptions{ + // Test relies on no dentry being held in the cache. + maxCachedDentries: 0, + }, + } + + ctx := contexttest.Context(t) + attr := &p9.Attr{ + Mode: p9.ModeRegular, + } + mask := p9.AttrMask{ + Mode: true, + Size: true, + } + parent, err := fs.newDentry(ctx, p9file{}, p9.QID{}, mask, attr) + if err != nil { + t.Fatalf("fs.newDentry(): %v", err) + } + + child, err := fs.newDentry(ctx, p9file{}, p9.QID{}, mask, attr) + if err != nil { + t.Fatalf("fs.newDentry(): %v", err) + } + parent.IncRef() // reference held by child on its parent. + parent.vfsd.InsertChild(&child.vfsd, "child") + + child.checkCachingLocked() + if got := atomic.LoadInt64(&child.refs); got != -1 { + t.Fatalf("child.refs=%d, want: -1", got) + } + // Parent will also be destroyed when child reference is removed. + if got := atomic.LoadInt64(&parent.refs); got != -1 { + t.Fatalf("parent.refs=%d, want: -1", got) + } + child.checkCachingLocked() + child.checkCachingLocked() +} diff --git a/test/syscalls/linux/open.cc b/test/syscalls/linux/open.cc index 267ae19f6..640fe6bfc 100644 --- a/test/syscalls/linux/open.cc +++ b/test/syscalls/linux/open.cc @@ -186,6 +186,28 @@ TEST_F(OpenTest, OpenNoFollowStillFollowsLinksInPath) { ASSERT_NO_ERRNO_AND_VALUE(Open(path_via_symlink, O_RDONLY | O_NOFOLLOW)); } +// Test that open(2) can follow symlinks that point back to the same tree. +// Test sets up files as follows: +// root/child/symlink => redirects to ../.. +// root/child/target => regular file +// +// open("root/child/symlink/root/child/file") +TEST_F(OpenTest, SymlinkRecurse) { + auto root = + ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDirIn(GetAbsoluteTestTmpdir())); + auto child = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateDirIn(root.path())); + auto symlink = ASSERT_NO_ERRNO_AND_VALUE( + TempPath::CreateSymlinkTo(child.path(), "../..")); + auto target = ASSERT_NO_ERRNO_AND_VALUE( + TempPath::CreateFileWith(child.path(), "abc", 0644)); + auto path_via_symlink = + JoinPath(symlink.path(), Basename(root.path()), Basename(child.path()), + Basename(target.path())); + const auto contents = + ASSERT_NO_ERRNO_AND_VALUE(GetContents(path_via_symlink)); + ASSERT_EQ(contents, "abc"); +} + TEST_F(OpenTest, Fault) { char* totally_not_null = nullptr; ASSERT_THAT(open(totally_not_null, O_RDONLY), SyscallFailsWithErrno(EFAULT)); |