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. 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 v3: - rename cb_session_changed to nfsd4_cb_session_changed - rename restart_callback to requeue_callback, and rename need_restart: label to requeue: - don't increment seq_nr on -ESERVERFAULT - comment cleanups - drop client-side rpc patch (will send separately) - Link to v2: https://lore.kernel.org/r/20250129-nfsd-6-14-v2-0-2700c92f3e44@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 (6): 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() fs/nfsd/nfs4callback.c | 217 +++++++++++++++++++++++++++++++++++-------------- fs/nfsd/nfs4state.c | 45 +++++++++- fs/nfsd/state.h | 6 +- fs/nfsd/trace.h | 6 +- 4 files changed, 204 insertions(+), 70 deletions(-) --- base-commit: a05af3c6103b703d1d38d8180b3ebbe0a03c2f07 change-id: 20250123-nfsd-6-14-b0797e385dc0 Best regards, -- Jeff Layton <jlayton@xxxxxxxxxx>
