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From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Thu, 29 Oct 2015 13:53:37 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r290140 - head/sys/kern
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Author: hselasky
Date: Thu Oct 29 13:53:37 2015
New Revision: 290140
URL: https://svnweb.freebsd.org/changeset/base/290140

Log:
  Add missing NULL check in physio().
  
  When destroying a character device the si_devsw field is set to NULL
  before all references are gone, to indicate the character device is
  going away. This can cause a NULL-dereference fault inside physio().
  
  The callers of physio() should own a thread reference on the cdev and
  if si_devsw is seen as non-NULL, it is usable during the execution of
  the function. Else an ENXIO error code is returned.
  
  Reviewed by:	kib
  MFC after:	2 weeks

Modified:
  head/sys/kern/kern_physio.c

Modified: head/sys/kern/kern_physio.c
==============================================================================
--- head/sys/kern/kern_physio.c	Thu Oct 29 10:31:44 2015	(r290139)
+++ head/sys/kern/kern_physio.c	Thu Oct 29 13:53:37 2015	(r290140)
@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 int
 physio(struct cdev *dev, struct uio *uio, int ioflag)
 {
+	struct cdevsw *csw;
 	struct buf *pbuf;
 	struct bio *bp;
 	struct vm_page **pages;
@@ -46,6 +47,11 @@ physio(struct cdev *dev, struct uio *uio
 	int error, i, npages, maxpages;
 	vm_prot_t prot;
 
+	csw = dev->si_devsw;
+	/* check if character device is being destroyed */
+	if (csw == NULL)
+		return (ENXIO);
+
 	/* XXX: sanity check */
 	if(dev->si_iosize_max < PAGE_SIZE) {
 		printf("WARNING: %s si_iosize_max=%d, using DFLTPHYS.\n",
@@ -165,7 +171,7 @@ physio(struct cdev *dev, struct uio *uio
 				}
 			}
 
-			dev->si_devsw->d_strategy(bp);
+			csw->d_strategy(bp);
 			if (uio->uio_rw == UIO_READ)
 				biowait(bp, "physrd");
 			else