From 6f60a2b0a27a742690aa6acd5df1912ccb5fc8d3 Mon Sep 17 00:00:00 2001 From: Etienne Perot Date: Thu, 3 Dec 2020 06:18:03 -0800 Subject: Implement `fcntl` options `F_GETSIG` and `F_SETSIG`. These options allow overriding the signal that gets sent to the process when I/O operations are available on the file descriptor, rather than the default `SIGIO` signal. Doing so also populates `siginfo` to contain extra information about which file descriptor caused the event (`si_fd`) and what events happened on it (`si_band`). The logic around which FD is populated within `si_fd` matches Linux's, which means it has some weird edge cases where that value may not actually refer to a file descriptor that is still valid. This CL also ports extra S/R logic regarding async handler in VFS2. Without this, async I/O handlers aren't properly re-registered after S/R. PiperOrigin-RevId: 345436598 --- pkg/sentry/kernel/epoll/epoll.go | 7 ++- pkg/sentry/kernel/fasync/BUILD | 2 + pkg/sentry/kernel/fasync/fasync.go | 96 ++++++++++++++++++++++++++++++++------ 3 files changed, 88 insertions(+), 17 deletions(-) (limited to 'pkg/sentry/kernel') diff --git a/pkg/sentry/kernel/epoll/epoll.go b/pkg/sentry/kernel/epoll/epoll.go index 15519f0df..61aeca044 100644 --- a/pkg/sentry/kernel/epoll/epoll.go +++ b/pkg/sentry/kernel/epoll/epoll.go @@ -273,7 +273,7 @@ func (e *EventPoll) ReadEvents(max int) []linux.EpollEvent { // // Callback is called when one of the files we're polling becomes ready. It // moves said file to the readyList if it's currently in the waiting list. -func (p *pollEntry) Callback(*waiter.Entry) { +func (p *pollEntry) Callback(*waiter.Entry, waiter.EventMask) { e := p.epoll e.listsMu.Lock() @@ -306,9 +306,8 @@ func (e *EventPoll) initEntryReadiness(entry *pollEntry) { f.EventRegister(&entry.waiter, entry.mask) // Check if the file happens to already be in a ready state. - ready := f.Readiness(entry.mask) & entry.mask - if ready != 0 { - entry.Callback(&entry.waiter) + if ready := f.Readiness(entry.mask) & entry.mask; ready != 0 { + entry.Callback(&entry.waiter, ready) } } diff --git a/pkg/sentry/kernel/fasync/BUILD b/pkg/sentry/kernel/fasync/BUILD index 2b3955598..f855f038b 100644 --- a/pkg/sentry/kernel/fasync/BUILD +++ b/pkg/sentry/kernel/fasync/BUILD @@ -8,11 +8,13 @@ go_library( visibility = ["//:sandbox"], deps = [ "//pkg/abi/linux", + "//pkg/sentry/arch", "//pkg/sentry/fs", "//pkg/sentry/kernel", "//pkg/sentry/kernel/auth", "//pkg/sentry/vfs", "//pkg/sync", + "//pkg/syserror", "//pkg/waiter", ], ) diff --git a/pkg/sentry/kernel/fasync/fasync.go b/pkg/sentry/kernel/fasync/fasync.go index 153d2cd9b..b66d61c6f 100644 --- a/pkg/sentry/kernel/fasync/fasync.go +++ b/pkg/sentry/kernel/fasync/fasync.go @@ -17,22 +17,45 @@ package fasync import ( "gvisor.dev/gvisor/pkg/abi/linux" + "gvisor.dev/gvisor/pkg/sentry/arch" "gvisor.dev/gvisor/pkg/sentry/fs" "gvisor.dev/gvisor/pkg/sentry/kernel" "gvisor.dev/gvisor/pkg/sentry/kernel/auth" "gvisor.dev/gvisor/pkg/sentry/vfs" "gvisor.dev/gvisor/pkg/sync" + "gvisor.dev/gvisor/pkg/syserror" "gvisor.dev/gvisor/pkg/waiter" ) -// New creates a new fs.FileAsync. -func New() fs.FileAsync { - return &FileAsync{} +// Table to convert waiter event masks into si_band siginfo codes. +// Taken from fs/fcntl.c:band_table. +var bandTable = map[waiter.EventMask]int64{ + // POLL_IN + waiter.EventIn: linux.EPOLLIN | linux.EPOLLRDNORM, + // POLL_OUT + waiter.EventOut: linux.EPOLLOUT | linux.EPOLLWRNORM | linux.EPOLLWRBAND, + // POLL_ERR + waiter.EventErr: linux.EPOLLERR, + // POLL_PRI + waiter.EventPri: linux.EPOLLPRI | linux.EPOLLRDBAND, + // POLL_HUP + waiter.EventHUp: linux.EPOLLHUP | linux.EPOLLERR, } -// NewVFS2 creates a new vfs.FileAsync. -func NewVFS2() vfs.FileAsync { - return &FileAsync{} +// New returns a function that creates a new fs.FileAsync with the given file +// descriptor. +func New(fd int) func() fs.FileAsync { + return func() fs.FileAsync { + return &FileAsync{fd: fd} + } +} + +// NewVFS2 returns a function that creates a new vfs.FileAsync with the given +// file descriptor. +func NewVFS2(fd int) func() vfs.FileAsync { + return func() vfs.FileAsync { + return &FileAsync{fd: fd} + } } // FileAsync sends signals when the registered file is ready for IO. @@ -42,6 +65,12 @@ type FileAsync struct { // e is immutable after first use (which is protected by mu below). e waiter.Entry + // fd is the file descriptor to notify about. + // It is immutable, set at allocation time. This matches Linux semantics in + // fs/fcntl.c:fasync_helper. + // The fd value is passed to the signal recipient in siginfo.si_fd. + fd int + // regMu protects registeration and unregistration actions on e. // // regMu must be held while registration decisions are being made @@ -56,6 +85,10 @@ type FileAsync struct { mu sync.Mutex `state:"nosave"` requester *auth.Credentials registered bool + // signal is the signal to deliver upon I/O being available. + // The default value ("zero signal") means the default SIGIO signal will be + // delivered. + signal linux.Signal // Only one of the following is allowed to be non-nil. recipientPG *kernel.ProcessGroup @@ -64,10 +97,10 @@ type FileAsync struct { } // Callback sends a signal. -func (a *FileAsync) Callback(e *waiter.Entry) { +func (a *FileAsync) Callback(e *waiter.Entry, mask waiter.EventMask) { a.mu.Lock() + defer a.mu.Unlock() if !a.registered { - a.mu.Unlock() return } t := a.recipientT @@ -80,19 +113,34 @@ func (a *FileAsync) Callback(e *waiter.Entry) { } if t == nil { // No recipient has been registered. - a.mu.Unlock() return } c := t.Credentials() // Logic from sigio_perm in fs/fcntl.c. - if a.requester.EffectiveKUID == 0 || + permCheck := (a.requester.EffectiveKUID == 0 || a.requester.EffectiveKUID == c.SavedKUID || a.requester.EffectiveKUID == c.RealKUID || a.requester.RealKUID == c.SavedKUID || - a.requester.RealKUID == c.RealKUID { - t.SendSignal(kernel.SignalInfoPriv(linux.SIGIO)) + a.requester.RealKUID == c.RealKUID) + if !permCheck { + return } - a.mu.Unlock() + signalInfo := &arch.SignalInfo{ + Signo: int32(linux.SIGIO), + Code: arch.SignalInfoKernel, + } + if a.signal != 0 { + signalInfo.Signo = int32(a.signal) + signalInfo.SetFD(uint32(a.fd)) + var band int64 + for m, bandCode := range bandTable { + if m&mask != 0 { + band |= bandCode + } + } + signalInfo.SetBand(band) + } + t.SendSignal(signalInfo) } // Register sets the file which will be monitored for IO events. @@ -186,3 +234,25 @@ func (a *FileAsync) ClearOwner() { a.recipientTG = nil a.recipientPG = nil } + +// Signal returns which signal will be sent to the signal recipient. +// A value of zero means the signal to deliver wasn't customized, which means +// the default signal (SIGIO) will be delivered. +func (a *FileAsync) Signal() linux.Signal { + a.mu.Lock() + defer a.mu.Unlock() + return a.signal +} + +// SetSignal overrides which signal to send when I/O is available. +// The default behavior can be reset by specifying signal zero, which means +// to send SIGIO. +func (a *FileAsync) SetSignal(signal linux.Signal) error { + if signal != 0 && !signal.IsValid() { + return syserror.EINVAL + } + a.mu.Lock() + defer a.mu.Unlock() + a.signal = signal + return nil +} -- cgit v1.2.3