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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Fri, 22 Jan 2016 20:35:20 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r294596 - head/sys/kern
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Author: kib
Date: Fri Jan 22 20:35:20 2016
New Revision: 294596
URL: https://svnweb.freebsd.org/changeset/base/294596

Log:
  The struct file f_advice member is overlaid with the devfs f_cdevpriv
  data.  If vnode bypass for devfs file failed, vn_read/vn_write are
  called and might try to dereference f_advice.  Limit the accesses to
  f_advice to VREG vnodes only, which is the type ensured by
  posix_fadvise().
  
  The f_advice for regular files is protected by mtxpool lock.  Recheck
  that f_advice is not NULL after lock is taken.
  
  Reported and tested by:	bde
  Sponsored by:	The FreeBSD Foundation
  MFC after:	3 weeks

Modified:
  head/sys/kern/vfs_vnops.c

Modified: head/sys/kern/vfs_vnops.c
==============================================================================
--- head/sys/kern/vfs_vnops.c	Fri Jan 22 20:30:51 2016	(r294595)
+++ head/sys/kern/vfs_vnops.c	Fri Jan 22 20:35:20 2016	(r294596)
@@ -743,12 +743,13 @@ get_advice(struct file *fp, struct uio *
 	int ret;
 
 	ret = POSIX_FADV_NORMAL;
-	if (fp->f_advice == NULL)
+	if (fp->f_advice == NULL || fp->f_vnode->v_type != VREG)
 		return (ret);
 
 	mtxp = mtx_pool_find(mtxpool_sleep, fp);
 	mtx_lock(mtxp);
-	if (uio->uio_offset >= fp->f_advice->fa_start &&
+	if (fp->f_advice != NULL &&
+	    uio->uio_offset >= fp->f_advice->fa_start &&
 	    uio->uio_offset + uio->uio_resid <= fp->f_advice->fa_end)
 		ret = fp->f_advice->fa_advice;
 	mtx_unlock(mtxp);