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nfs/localio: must clear res.replen in nfs_local_read_done
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Otherwise memory corruption can occur due to NFSv3 LOCALIO reads
leaving garbage in res.replen:
- nfs3_read_done() copies that into server->read_hdrsize; from there
  nfs3_proc_read_setup() copies it to args.replen in new requests.
- nfs3_xdr_enc_read3args() passes that to rpc_prepare_reply_pages()
  which includes it in hdrsize for xdr_init_pages, so that rq_rcv_buf
  contains a ridiculous len.
- This is copied to rq_private_buf and xs_read_stream_request()
  eventually passes the kvec to sock_recvmsg() which receives incoming
  data into entirely the wrong place.

This is easily reproduced with NFSv3 LOCALIO that is servicing reads
when it is made to pivot back to using normal RPC.  This switch back
to using normal NFSv3 with RPC can occur for a few reasons but this
issue was exposed with a test that stops and then restarts the NFSv3
server while LOCALIO is performing heavy read IO.

Fixes: 70ba381 ("nfs: add LOCALIO support")
Reported-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: NeilBrown <neilb@suse.de>
Co-developed-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
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neilbrown authored and Trond Myklebust committed Nov 10, 2024
1 parent 2fdb05d commit 650703b
Showing 1 changed file with 6 additions and 0 deletions.
6 changes: 6 additions & 0 deletions fs/nfs/localio.c
Original file line number Diff line number Diff line change
Expand Up @@ -351,6 +351,12 @@ nfs_local_read_done(struct nfs_local_kiocb *iocb, long status)

nfs_local_pgio_done(hdr, status);

/*
* Must clear replen otherwise NFSv3 data corruption will occur
* if/when switching from LOCALIO back to using normal RPC.
*/
hdr->res.replen = 0;

if (hdr->res.count != hdr->args.count ||
hdr->args.offset + hdr->res.count >= i_size_read(file_inode(filp)))
hdr->res.eof = true;
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