From fca26a3fc19ed02278aa2a150af82d43db0302cb Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Tue, 2 Jun 2026 12:23:13 -0400 Subject: nfsd: defer vfree of compound ops to fix rpc_status UAF MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The rpc_status netlink dumpit walks every in-flight svc_rqst under rcu_read_lock and, for NFSv4 requests, reads opnums out of args->ops[]. But args->ops is a separate vmalloc buffer freed synchronously by vfree() in nfsd4_release_compoundargs() at the end of every compound. The dumpit's rcu_read_lock pins the svc_rqst struct itself (freed via kfree_rcu), but nothing defers the vfree of the ops buffer across the RCU grace period. A concurrent compound completion can therefore free the buffer while the dumpit is reading it — a use-after-free on vmalloc memory. The trailing seqcount recheck (smp_load_acquire of rq_status_counter) cannot undo a load that already retired against freed memory. Fix by replacing vfree(args->ops) with kvfree_rcu_mightsleep(), which defers the free until after an RCU grace period. This makes the existing rcu_read_lock in the dumpit sufficient to protect the read. The tradeoff is that completed compound ops buffers (up to 200 * sizeof(struct nfsd4_op)) persist in memory slightly longer, across one grace period, before being reclaimed. Fixes: bd9d6a3efa97 ("NFSD: add rpc_status netlink support") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260602-nfsd-testing-v2-1-e4ea62e3cd5c@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 2e0097b2d1d9..b9037d99b564 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -6435,8 +6435,10 @@ void nfsd4_release_compoundargs(struct svc_rqst *rqstp) struct nfsd4_compoundargs *args = rqstp->rq_argp; if (args->ops != args->iops) { - vfree(args->ops); + void *old_ops = args->ops; + args->ops = args->iops; + kvfree_rcu_mightsleep(old_ops); } while (args->to_free) { struct svcxdr_tmpbuf *tb = args->to_free; -- cgit v1.2.3