[src/trunk]: src/sys/kern vnodeops(9): Take exclusive lock in read/seek for f...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/9299ff011227
branches:  trunk
changeset: 368810:9299ff011227
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Aug 06 21:21:10 2022 +0000

description:
vnodeops(9): Take exclusive lock in read/seek for f_offset update.

Otherwise concurrent readers/seekers might clobber it.

diffstat:

 sys/kern/vfs_vnops.c |  14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diffs (42 lines):

diff -r 09d3f1537bac -r 9299ff011227 sys/kern/vfs_vnops.c
--- a/sys/kern/vfs_vnops.c      Sat Aug 06 20:16:42 2022 +0000
+++ b/sys/kern/vfs_vnops.c      Sat Aug 06 21:21:10 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_vnops.c,v 1.234 2022/07/18 04:30:30 thorpej Exp $  */
+/*     $NetBSD: vfs_vnops.c,v 1.235 2022/08/06 21:21:10 riastradh Exp $        */
 
 /*-
  * Copyright (c) 2009 The NetBSD Foundation, Inc.
@@ -66,7 +66,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_vnops.c,v 1.234 2022/07/18 04:30:30 thorpej Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_vnops.c,v 1.235 2022/08/06 21:21:10 riastradh Exp $");
 
 #include "veriexec.h"
 
@@ -647,7 +647,10 @@
                ioflag |= IO_ALTSEMANTICS;
        if (fflag & FDIRECT)
                ioflag |= IO_DIRECT;
-       vn_lock(vp, LK_SHARED | LK_RETRY);
+       if (offset == &fp->f_offset && (flags & FOF_UPDATE_OFFSET) != 0)
+               vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+       else
+               vn_lock(vp, LK_SHARED | LK_RETRY);
        uio->uio_offset = *offset;
        count = uio->uio_resid;
        error = VOP_READ(vp, uio, ioflag, cred);
@@ -1135,7 +1138,10 @@
        if (vp->v_type == VFIFO)
                return ESPIPE;
 
-       vn_lock(vp, LK_SHARED | LK_RETRY);
+       if (flags & FOF_UPDATE_OFFSET)
+               vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+       else
+               vn_lock(vp, LK_SHARED | LK_RETRY);
 
        /* Compute the old and new offsets.  */
        oldoff = fp->f_offset;