linux-kernel - Re: [PATCH 09/10] VFS: Remove read-only checks from dentry

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Message-Id: <E1Osh50-0005s0-V7@pomaz-ex.szeredi.hu>
Date:	Mon, 06 Sep 2010 21:10:10 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	NeilBrown <neilb@...e.de>
CC:	miklos@...redi.hu, linux-fsdevel@...r.kernel.org,
	haveblue@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] VFS: Remove read-only checks from dentry_permission

On Mon, 06 Sep 2010, NeilBrown wrote:
> It is not sufficient to depend on the the "filesystem is readonly"
> tests in dentry_permission as it does not check if the vfsmnt is
> readonly.
> All call sites already call mnt_want_write or __mnt_is_readonly which
> includes the test on MS_RDONLY.

Last time I checked I found some holes (in nfsd IIRC).  That was a
long time ago and things may have changed.

That check could be replaced with a

		if (IS_RDONLY(inode) &&
		    (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
			BUG();

which would catch these cases but only if the superblock was marked
r/o.  Otherwise it's basically impossible to make sure the callers of
the VFS play by the rules.  That was one reason I advocated a
path_... interface for the VFS instead of the current dentry based
one, but Al didn't like it.

Thanks,
Miklos
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