Save previous content of the td_fpop before storing the current

filedescriptor into it. Make sure that td_fpop is NULL when calling
d_mmap from dev_pager_getpages().

Change guards against td_fpop field being non-NULL with private state
for another device, and against sudden clearing the td_fpop. This
could occur when either a driver method calls another driver through
the filedescriptor operation, or a page fault happen while driver is
writing to a memory backed by another driver.

Noted by:	rwatson
Tested by:	rnoland
MFC after:	3 days

1 files changed, 27 insertions, 12 deletions

diff --git a/sys/fs/devfs/devfs_vnops.c b/sys/fs/devfs/devfs_vnops.c
index 94ea0dd..54afebe 100644
--- a/sys/fs/devfs/devfs_vnops.c
+++ b/sys/fs/devfs/devfs_vnops.c
@@ -466,10 +466,12 @@ static int
 devfs_close_f(struct file *fp, struct thread *td)
 {
 	int error;
+	struct file *fpop;
 
-	curthread->td_fpop = fp;
+	fpop = td->td_fpop;
+	td->td_fpop = fp;
 	error = vnops.fo_close(fp, td);
-	curthread->td_fpop = NULL;
+	td->td_fpop = fpop;
 	return (error);
 }
 
@@ -559,14 +561,16 @@ devfs_ioctl_f(struct file *fp, u_long com, void *data, struct ucred *cred, struc
 	int error, i;
 	const char *p;
 	struct fiodgname_arg *fgn;
+	struct file *fpop;
 
+	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw);
 	if (error)
 		return (error);
 
 	if (com == FIODTYPE) {
 		*(int *)data = dsw->d_flags & D_TYPEMASK;
-		td->td_fpop = NULL;
+		td->td_fpop = fpop;
 		dev_relthread(dev);
 		return (0);
 	} else if (com == FIODGNAME) {
@@ -577,7 +581,7 @@ devfs_ioctl_f(struct file *fp, u_long com, void *data, struct ucred *cred, struc
 			error = EINVAL;
 		else
 			error = copyout(p, fgn->buf, i);
-		td->td_fpop = NULL;
+		td->td_fpop = fpop;
 		dev_relthread(dev);
 		return (error);
 	}
@@ -618,12 +622,16 @@ devfs_kqfilter_f(struct file *fp, struct knote *kn)
 	struct cdev *dev;
 	struct cdevsw *dsw;
 	int error;
+	struct file *fpop;
+	struct thread *td;
 
+	td = curthread;
+	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw);
 	if (error)
 		return (error);
 	error = dsw->d_kqfilter(dev, kn);
-	curthread->td_fpop = NULL;
+	td->td_fpop = fpop;
 	dev_relthread(dev);
 	return (error);
 }
@@ -840,6 +848,7 @@ devfs_open(struct vop_open_args *ap)
 	struct file *fp = ap->a_fp;
 	int error;
 	struct cdevsw *dsw;
+	struct file *fpop;
 
 	if (vp->v_type == VBLK)
 		return (ENXIO);
@@ -861,15 +870,15 @@ devfs_open(struct vop_open_args *ap)
 
 	VOP_UNLOCK(vp, 0);
 
-	if (fp != NULL) {
-		td->td_fpop = fp;
+	fpop = td->td_fpop;
+	td->td_fpop = fp;
+	if (fp != NULL)
 		fp->f_data = dev;
-	}
 	if (dsw->d_fdopen != NULL)
 		error = dsw->d_fdopen(dev, ap->a_mode, td, fp);
 	else
 		error = dsw->d_open(dev, ap->a_mode, S_IFCHR, td);
-	td->td_fpop = NULL;
+	td->td_fpop = fpop;
 
 	vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 
@@ -919,12 +928,14 @@ devfs_poll_f(struct file *fp, int events, struct ucred *cred, struct thread *td)
 	struct cdev *dev;
 	struct cdevsw *dsw;
 	int error;
+	struct file *fpop;
 
+	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw);
 	if (error)
 		return (error);
 	error = dsw->d_poll(dev, events, td);
-	curthread->td_fpop = NULL;
+	td->td_fpop = fpop;
 	dev_relthread(dev);
 	return(error);
 }
@@ -947,7 +958,9 @@ devfs_read_f(struct file *fp, struct uio *uio, struct ucred *cred, int flags, st
 	struct cdev *dev;
 	int ioflag, error, resid;
 	struct cdevsw *dsw;
+	struct file *fpop;
 
+	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw);
 	if (error)
 		return (error);
@@ -962,7 +975,7 @@ devfs_read_f(struct file *fp, struct uio *uio, struct ucred *cred, int flags, st
 	error = dsw->d_read(dev, uio, ioflag);
 	if (uio->uio_resid != resid || (error == 0 && resid != 0))
 		vfs_timestamp(&dev->si_atime);
-	curthread->td_fpop = NULL;
+	td->td_fpop = fpop;
 	dev_relthread(dev);
 
 	if ((flags & FOF_OFFSET) == 0)
@@ -1383,7 +1396,9 @@ devfs_write_f(struct file *fp, struct uio *uio, struct ucred *cred, int flags, s
 	struct cdev *dev;
 	int error, ioflag, resid;
 	struct cdevsw *dsw;
+	struct file *fpop;
 
+	fpop = td->td_fpop;
 	error = devfs_fp_check(fp, &dev, &dsw);
 	if (error)
 		return (error);
@@ -1401,7 +1416,7 @@ devfs_write_f(struct file *fp, struct uio *uio, struct ucred *cred, int flags, s
 		vfs_timestamp(&dev->si_ctime);
 		dev->si_mtime = dev->si_ctime;
 	}
-	curthread->td_fpop = NULL;
+	td->td_fpop = fpop;
 	dev_relthread(dev);
 
 	if ((flags & FOF_OFFSET) == 0)