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Wed, 19 Aug 2026 00:47:19 -0700 (PDT) From: Tien Phan To: security@kernel.org Cc: Greg KH , Chuck Lever , NeilBrown , Jeff Layton , stable@vger.kernel.org, Tien Phan Subject: [PATCH v3] nfsd: fix use-after-free of DRC slot in nfsd4_sequence() Date: Wed, 19 Aug 2026 16:47:01 +0900 Message-Id: <20260819074701.1312702-1-tienpp@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260819054326.1265334-1-tienpp@gmail.com> References: <20260819054326.1265334-1-tienpp@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit nfsd4_sequence() loads the slot for the client-supplied seq->slotid (bounded only by se_fchannel.maxreqs), then on the reduce-ack path frees every slot in [se_target_maxslots, maxreqs) with free_session_slots() without checking that the loaded slot is outside that range. Once the DRC shrinker has lowered se_target_maxslots below maxreqs, a client using seq->slotid >= se_target_maxslots has its own slot freed and then dereferenced and written (slot->sl_seqid, cstate->slot): a use-after-free. Reject such a slotid before freeing the slots. Fixes: fc8738c68d0b ("nfsd: add support for freeing unused session-DRC slots") Cc: stable@vger.kernel.org # 6.14+ Reported-by: Sentinel (automated analysis agent) Assisted-by: Claude (Anthropic) Signed-off-by: Tien Phan --- v3: trim commit message; drop the added in-code comment (Greg KH). v2: add Reported-by:/Assisted-by: trailers (Greg KH); fix NeilBrown address. v1: https://lore.kernel.org/all/20260819054326.1265334-1-tienpp@gmail.com/ fs/nfsd/nfs4state.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c index a42f34842d77..def1ea534e18 100644 --- a/fs/nfsd/nfs4state.c +++ b/fs/nfsd/nfs4state.c @@ -4575,9 +4575,14 @@ nfsd4_sequence(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate, if (session->se_target_maxslots < session->se_fchannel.maxreqs && slot->sl_generation == session->se_slot_gen && - seq->maxslots <= session->se_target_maxslots) + seq->maxslots <= session->se_target_maxslots) { /* Client acknowledged our reduce maxreqs */ + if (seq->slotid >= session->se_target_maxslots) { + status = nfserr_badslot; + goto out_put_session; + } free_session_slots(session, session->se_target_maxslots); + } buflen = (seq->cachethis) ? session->se_fchannel.maxresp_cached : -- 2.34.1