From 807a080d9574e42dae83bb8bd0863b110b98a858 Mon Sep 17 00:00:00 2001
From: Dean Deng <deandeng@google.com>
Date: Thu, 31 Dec 2020 09:48:56 -0800
Subject: Add missing error checks for FileDescription.Init.

Syzkaller discovered this bug in pipefs by doing something quite strange:
creat(&(0x7f0000002a00)='./file1\x00', 0x0)
mount(&(0x7f0000000440)=ANY=[], &(0x7f00000002c0)='./file1\x00', &(0x7f0000000300)='devtmpfs\x00', 0x20000d, 0x0)
creat(&(0x7f0000000000)='./file1/file0\x00', 0x0)

This can be reproduced with:
touch mymount
mkfifo /dev/mypipe
mount -o ro -t devtmpfs devtmpfs mymount
echo 123 > mymount/mypipe

PiperOrigin-RevId: 349687714
---
 pkg/sentry/kernel/pipe/vfs.go | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

(limited to 'pkg/sentry/kernel/pipe/vfs.go')

diff --git a/pkg/sentry/kernel/pipe/vfs.go b/pkg/sentry/kernel/pipe/vfs.go
index 7b23cbe86..2d47d2e82 100644
--- a/pkg/sentry/kernel/pipe/vfs.go
+++ b/pkg/sentry/kernel/pipe/vfs.go
@@ -63,10 +63,19 @@ func NewVFSPipe(isNamed bool, sizeBytes int64) *VFSPipe {
 // ReaderWriterPair returns read-only and write-only FDs for vp.
 //
 // Preconditions: statusFlags should not contain an open access mode.
-func (vp *VFSPipe) ReaderWriterPair(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, *vfs.FileDescription) {
+func (vp *VFSPipe) ReaderWriterPair(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32) (*vfs.FileDescription, *vfs.FileDescription, error) {
 	// Connected pipes share the same locks.
 	locks := &vfs.FileLocks{}
-	return vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags, locks), vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags, locks)
+	r, err := vp.newFD(mnt, vfsd, linux.O_RDONLY|statusFlags, locks)
+	if err != nil {
+		return nil, nil, err
+	}
+	w, err := vp.newFD(mnt, vfsd, linux.O_WRONLY|statusFlags, locks)
+	if err != nil {
+		r.DecRef(ctx)
+		return nil, nil, err
+	}
+	return r, w, nil
 }
 
 // Allocate implements vfs.FileDescriptionImpl.Allocate.
@@ -85,7 +94,10 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 		return nil, syserror.EINVAL
 	}
 
-	fd := vp.newFD(mnt, vfsd, statusFlags, locks)
+	fd, err := vp.newFD(mnt, vfsd, statusFlags, locks)
+	if err != nil {
+		return nil, err
+	}
 
 	// Named pipes have special blocking semantics during open:
 	//
@@ -137,16 +149,18 @@ func (vp *VFSPipe) Open(ctx context.Context, mnt *vfs.Mount, vfsd *vfs.Dentry, s
 }
 
 // Preconditions: vp.mu must be held.
-func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *vfs.FileLocks) *vfs.FileDescription {
+func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, locks *vfs.FileLocks) (*vfs.FileDescription, error) {
 	fd := &VFSPipeFD{
 		pipe: &vp.pipe,
 	}
 	fd.LockFD.Init(locks)
-	fd.vfsfd.Init(fd, statusFlags, mnt, vfsd, &vfs.FileDescriptionOptions{
+	if err := fd.vfsfd.Init(fd, statusFlags, mnt, vfsd, &vfs.FileDescriptionOptions{
 		DenyPRead:         true,
 		DenyPWrite:        true,
 		UseDentryMetadata: true,
-	})
+	}); err != nil {
+		return nil, err
+	}
 
 	switch {
 	case fd.vfsfd.IsReadable() && fd.vfsfd.IsWritable():
@@ -160,7 +174,7 @@ func (vp *VFSPipe) newFD(mnt *vfs.Mount, vfsd *vfs.Dentry, statusFlags uint32, l
 		panic("invalid pipe flags: must be readable, writable, or both")
 	}
 
-	return &fd.vfsfd
+	return &fd.vfsfd, nil
 }
 
 // VFSPipeFD implements vfs.FileDescriptionImpl for pipes. It also implements
-- 
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