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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-Type: text/plain; charset="us-ascii" 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 Hi Linus, Could you apply this fix please? Thanks, David --- When an AFS FS.StoreData RPC call is made, amongst other things it is give= n 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 se= t 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 loc= k 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, s= truct 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; = 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); = switch (op->error) {