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From: "J. Bruce Fields" <bfields@redhat.com>
To: linux-nfs@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, "J. Bruce Fields" <bfields@redhat.com>
Subject: [PATCH 1/2] nfsd: allow fh_want_write to be called twice
Date: Wed, 15 May 2019 21:20:06 -0400	[thread overview]
Message-ID: <1557969619-17157-2-git-send-email-bfields@redhat.com> (raw)
In-Reply-To: <1557969619-17157-1-git-send-email-bfields@redhat.com>

From: "J. Bruce Fields" <bfields@redhat.com>

A fuzzer recently triggered lockdep warnings about potential sb_writers
deadlocks caused by fh_want_write().

Looks like we aren't careful to pair each fh_want_write() with an
fh_drop_write().

It's not normally a problem since fh_put() will call fh_drop_write() for
us.  And was OK for NFSv3 where we'd do one operation that might call
fh_want_write(), and then put the filehandle.

But an NFSv4 protocol fuzzer can do weird things like call unlink twice
in a compound, and then we get into trouble.

I'm a little worried about this approach of just leaving everything to
fh_put().  But I think there are probably a lot of
fh_want_write()/fh_drop_write() imbalances so for now I think we need it
to be more forgiving.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>
---
 fs/nfsd/vfs.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index a7e107309f76..db351247892d 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -120,8 +120,11 @@ void		nfsd_put_raparams(struct file *file, struct raparms *ra);
 
 static inline int fh_want_write(struct svc_fh *fh)
 {
-	int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
+	int ret;
 
+	if (fh->fh_want_write)
+		return 0;
+	ret = mnt_want_write(fh->fh_export->ex_path.mnt);
 	if (!ret)
 		fh->fh_want_write = true;
 	return ret;
-- 
2.21.0


  reply	other threads:[~2019-05-16  1:46 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16  1:20 [PATCH 00/12] exposing knfsd state to userspace J. Bruce Fields
2019-05-16  1:20 ` J. Bruce Fields [this message]
2019-05-18 20:04   ` [PATCH 1/2] nfsd: allow fh_want_write to be called twice J. Bruce Fields
2019-05-16  1:20 ` [PATCH 01/12] nfsd: persist nfsd filesystem across mounts J. Bruce Fields
2019-05-16  1:20 ` [PATCH 2/2] nfsd: fh_drop_write in nfsd_unlink J. Bruce Fields
2019-05-16  1:20 ` [PATCH 02/12] nfsd: rename cl_refcount J. Bruce Fields
2019-05-16  1:20 ` [PATCH 03/12] nfsd4: use reference count to free client J. Bruce Fields
2019-05-16  1:20 ` [PATCH 04/12] nfsd: add nfsd/clients directory J. Bruce Fields
2019-05-16  1:20 ` [PATCH 05/12] nfsd: make client/ directory names small ints J. Bruce Fields
2019-05-16  1:20 ` [PATCH 06/12] nfsd4: add a client info file J. Bruce Fields
2019-05-16  1:20 ` [PATCH 07/12] nfsd: copy client's address including port number to cl_addr J. Bruce Fields
2019-05-16  1:20 ` [PATCH 08/12] nfsd: add more information to client info file J. Bruce Fields
2019-05-16  1:20 ` [PATCH 09/12] nfsd4: add file to display list of client's opens J. Bruce Fields
2019-05-16  1:20 ` [PATCH 10/12] nfsd: show lock and deleg stateids J. Bruce Fields
2019-05-16  1:20 ` [PATCH 11/12] nfsd4: show layout stateids J. Bruce Fields
2019-05-16  1:20 ` [PATCH 12/12] nfsd: allow forced expiration of NFSv4 clients J. Bruce Fields
  -- strict thread matches above, loose matches on Subject: below --
2019-05-13 15:27 [PATCH 0/2] nfsd shoudn't call mnt_want_write twice J. Bruce Fields
2019-05-13 15:27 ` [PATCH 1/2] nfsd: allow fh_want_write to be called twice J. Bruce Fields

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