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Date: Mon, 18 Mar 2019 13:29:49 -0700 From: Eric Biggers <ebiggers@...nel.org> To: Al Viro <viro@...iv.linux.org.uk> Cc: linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-mtd@...ts.infradead.org, linux-unionfs@...r.kernel.org, Sarthak Kukreti <sarthakkukreti@...omium.org>, Gao Xiang <gaoxiang25@...wei.com> Subject: Re: [PATCH 1/5] fscrypt: clean up and improve dentry revalidation On Sun, Mar 17, 2019 at 08:38:22PM +0000, Al Viro wrote: > On Sun, Mar 17, 2019 at 01:04:40PM -0700, Eric Biggers wrote: > > + /* > > + * Ciphertext name; valid if the directory's key is still unavailable. > > + * > > + * Note: since fscrypt forbids rename() on ciphertext names, it should > > + * be safe to access ->d_parent directly here. > > No, it is not. Again, d_splice_alias() on buggered fs image picking a reference > to your subdirectory when doing a lookup elsewhere. It can relocate the > damn thing, without rename() being allowed for _anything_. You're talking about directory hard links, right? E.g. if there's a directory with two links a/dir and b/dir, and fscrypt_d_revalidate() is running on 'dir' via a lookup in a/, it could be the case that b/dir is being concurrently looked up. Then the concurrent d_splice_alias() will move the whole dentry tree rooted at 'dir' from a/ to b/ in the dcache. Okay, it looks like you're right; I'll update my comment to clarify that dget_parent() is still needed... - Eric
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