5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chuck Lever <chuck.lever@xxxxxxxxxx> [ Upstream commit 8d915bbf39266bb66082c1e4980e123883f19830 ] We've discovered that delivering a CB_OFFLOAD operation can be unreliable in some pretty unremarkable situations. Examples include: - The server dropped the connection because it lost a forechannel NFSv4 request and wishes to force the client to retransmit - The GSS sequence number window under-flowed - A network partition occurred When that happens, all pending callback operations, including CB_OFFLOAD, are lost. NFSD does not retransmit them. Moreover, the Linux NFS client does not yet support sending an OFFLOAD_STATUS operation to probe whether an asynchronous COPY operation has finished. Thus, on Linux NFS clients, when a CB_OFFLOAD is lost, asynchronous COPY can hang until manually interrupted. I've tried a couple of remedies, but so far the side-effects are worse than the disease and they have had to be reverted. So temporarily force COPY operations to be synchronous so that the use of CB_OFFLOAD is avoided entirely. This is a fix that can easily be backported to LTS kernels. I am working on client patches that introduce an implementation of OFFLOAD_STATUS. Note that NFSD arbitrarily limits the size of a copy_file_range to 4MB to avoid indefinitely blocking an nfsd thread. A short COPY result is returned in that case, and the client can present a fresh COPY request for the remainder. Link: https://nvd.nist.gov/vuln/detail/CVE-2024-49974 [ cel: adjusted to apply to origin/linux-5.4.y ] Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- fs/nfsd/nfs4proc.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c index e38f873f98a7f..27e9754ad3b9d 100644 --- a/fs/nfsd/nfs4proc.c +++ b/fs/nfsd/nfs4proc.c @@ -1262,6 +1262,13 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, __be32 status; struct nfsd4_copy *async_copy = NULL; + /* + * Currently, async COPY is not reliable. Force all COPY + * requests to be synchronous to avoid client application + * hangs waiting for COPY completion. + */ + copy->cp_synchronous = 1; + status = nfsd4_verify_copy(rqstp, cstate, ©->cp_src_stateid, ©->nf_src, ©->cp_dst_stateid, ©->nf_dst); -- 2.43.0
