On Wed, Jan 29, 2025 at 09:27:02AM -0500, Jeff Layton wrote: > On Wed, 2025-01-29 at 09:21 -0500, J. Bruce Fields wrote: > > On Wed, Jan 29, 2025 at 08:39:53AM -0500, Jeff Layton wrote: > > > While looking over the CB_SEQUENCE error handling, I discovered that > > > callbacks don't hold a reference to a session, and the > > > clp->cl_cb_session could easily change between request and response. > > > If that happens at an inopportune time, there could be UAFs or weird > > > slot/sequence handling problems. > > > > Nobody should place too much faith in my understanding of how any of > > this works at this point, but.... My vague memory is that a lot of > > things are serialized simply by being run only on the cl_callback_wq. > > Modifying clp->cl_cb_session is such a thing. > > It is, but that doesn't save us here. The workqueue is just there to > submit jobs to the RPC client. Once that happens they are run via > rpciod's workqueue (and in parallel with one another since they're > async RPC calls). > > So, it's possible that while we're waiting for a response from one > callback, another is submitted, and that workqueue job changes the > clp->cl_cb_session. I think it calls rpc_shutdown_client() before changing clp->cl_cb_session. (Though I'm not sure whether rpc_shutdown_client guarantees that all rpc processing for the client is completed before returning?) --b. > > Thanks for taking a look, Bruce! > > > > > > This series changes the nfsd4_session to be RCU-freed, and then adds a > > > new method of session refcounting that is compatible with the old. > > > nfsd4_callback RPCs will now hold a lightweight reference to the session > > > in addition to the slot. Then, all of the callback handling is switched > > > to use that session instead of dereferencing clp->cb_cb_session. > > > I've also reworked the error handling in nfsd4_cb_sequence_done() > > > based on review comments, and lifted the v4.0 handing out of that > > > function. > > > > > > This passes pynfs, nfstests, and fstests for me, but I'm not sure how > > > much any of that stresses the backchannel's error handling. > > > > > > These should probably go in via Chuck's tree, but the last patch touches > > > some NFS cnd sunrpc client code, so it'd be good to have R-b's or A-b's > > > from Trond and/or Anna on that one. > > > > > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx> > > > --- > > > Changes in v2: > > > - make nfsd4_session be RCU-freed > > > - change code to keep reference to session over callback RPCs > > > - rework error handling in nfsd4_cb_sequence_done() > > > - move NFSv4.0 handling out of nfsd4_cb_sequence_done() > > > - Link to v1: https://lore.kernel.org/r/20250123-nfsd-6-14-v1-0-c1137a4fa2ae@xxxxxxxxxx > > > > > > --- > > > Jeff Layton (7): > > > nfsd: add routines to get/put session references for callbacks > > > nfsd: make clp->cl_cb_session be an RCU managed pointer > > > nfsd: add a cb_ses pointer to nfsd4_callback and use it instead of clp->cb_cb_session > > > nfsd: overhaul CB_SEQUENCE error handling > > > nfsd: remove unneeded forward declaration of nfsd4_mark_cb_fault() > > > nfsd: lift NFSv4.0 handling out of nfsd4_cb_sequence_done() > > > sunrpc: make rpc_restart_call() and rpc_restart_call_prepare() void return > > > > > > fs/nfs/nfs4proc.c | 12 ++- > > > fs/nfsd/nfs4callback.c | 212 ++++++++++++++++++++++++++++++++------------ > > > fs/nfsd/nfs4state.c | 43 ++++++++- > > > fs/nfsd/state.h | 6 +- > > > fs/nfsd/trace.h | 6 +- > > > include/linux/sunrpc/clnt.h | 4 +- > > > net/sunrpc/clnt.c | 7 +- > > > 7 files changed, 210 insertions(+), 80 deletions(-) > > > --- > > > base-commit: a05af3c6103b703d1d38d8180b3ebbe0a03c2f07 > > > change-id: 20250123-nfsd-6-14-b0797e385dc0 > > > > > > Best regards, > > > -- > > > Jeff Layton <jlayton@xxxxxxxxxx> > > -- > Jeff Layton <jlayton@xxxxxxxxxx>
