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Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells To: torvalds@linux-foundation.org cc: dhowells@redhat.com, Jeffrey Altman , Marc Dionne , linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] afs: Fix accidental truncation when storing data MIME-Version: 1.0 Content-ID: <1591987.1688498535.1@warthog.procyon.org.uk> Content-Transfer-Encoding: quoted-printable Date: Tue, 04 Jul 2023 20:22:15 +0100 Message-ID: <1591988.1688498535@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Hi Linus, Could you apply this fix please? Thanks, David Reported-by: Marc Dionne Reviewed-by: Jeffrey Altman Reviewed-by: Marc Dionne --- When an AFS FS.StoreData RPC call is made, amongst other things it is given the resultant file size to be. On the server, this is processed by truncating the file to new size and then writing the data. Now, kafs has a lock (vnode->io_lock) that serves to serialise operations against a specific vnode (ie. inode), but the parameters for the op are set before the lock is taken. This allows two writebacks (say sync and kswapd) to race - and if writes are ongoing the writeback for a later write could occur before the writeback for an earlier one if the latter gets interrupted. Note that afs_writepages() cannot take i_mutex and only takes a shared lock on vnode->validate_lock. Also note that the server does the truncation and the write inside a lock, so there's no problem at that end. Fix this by moving the calculation for the proposed new i_size inside the vnode->io_lock. Also reset the iterator (which we might have read from) and update the mtime setting there. Fixes: bd80d8a80e12 ("afs: Use ITER_XARRAY for writing") Reported-by: Marc Dionne Signed-off-by: David Howells Reviewed-by: Jeffrey Altman Reviewed-by: Marc Dionne cc: linux-afs@lists.infradead.org cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/3526895.1687960024@warthog.procyon.org.uk/ --- fs/afs/write.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/fs/afs/write.c b/fs/afs/write.c index 8750b99c3f56..c1f4391ccd7c 100644 --- a/fs/afs/write.c +++ b/fs/afs/write.c @@ -413,17 +413,19 @@ static int afs_store_data(struct afs_vnode *vnode, st= ruct iov_iter *iter, loff_t afs_op_set_vnode(op, 0, vnode); op->file[0].dv_delta =3D 1; op->file[0].modification =3D true; - op->store.write_iter =3D iter; op->store.pos =3D pos; op->store.size =3D size; - op->store.i_size =3D max(pos + size, vnode->netfs.remote_i_size); op->store.laundering =3D laundering; - op->mtime =3D vnode->netfs.inode.i_mtime; op->flags |=3D AFS_OPERATION_UNINTR; op->ops =3D &afs_store_data_operation; =20 try_next_key: afs_begin_vnode_operation(op); + + op->store.write_iter =3D iter; + op->store.i_size =3D max(pos + size, vnode->netfs.remote_i_size); + op->mtime =3D vnode->netfs.inode.i_mtime; + afs_wait_for_operation(op); =20 switch (op->error) {