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net/9p: fix race condition on rdma->state in trans_rdma.c

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[ Upstream commit 7d54894a1e ]

The rdma->state field is modified without holding req_lock in both
recv_done() and p9_cm_event_handler(), while rdma_request() accesses
the same field under the req_lock spinlock. This inconsistent locking
creates a race condition:

- recv_done() running in softirq completion context sets
  rdma->state = P9_RDMA_FLUSHING without acquiring req_lock

- p9_cm_event_handler() modifies rdma->state at multiple points
  (ADDR_RESOLVED, ROUTE_RESOLVED, ESTABLISHED, CLOSED) without
  req_lock

- rdma_request() uses spin_lock_irqsave(&rdma->req_lock, flags) to
  protect the read-modify-write of rdma->state

The race can cause lost state transitions: recv_done() or the CM
event handler could set state to FLUSHING/CLOSED while rdma_request()
is concurrently checking or modifying state under the lock, leading to
the FLUSHING transition being silently overwritten by CLOSING. This
corrupts the connection state machine and can cause use-after-free on
RDMA request objects during teardown.

Fix by adding req_lock protection to all rdma->state modifications in
recv_done() and p9_cm_event_handler(), matching the pattern already
used in rdma_request(). Use spin_lock_irqsave/spin_unlock_irqrestore
in the CM event handler since it can race with recv_done() which runs
in softirq context.

Tested with a kernel module that races two threads (simulating
rdma_request and recv_done/CM handler) on rdma->state with proper
locking: 5.5M+ FLUSHING writes over 27M iterations with 0 lost
transitions.

Fixes: 473c7dd1d7 ("9p/rdma: remove useless check in cm_event_handler")
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM:GLM-5.1
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Message-ID: <20260529073933.77315-1-zhaoyz24@mails.tsinghua.edu.cn>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Yizhou Zhao
2026-07-24 16:03:14 +02:00
committed by Greg Kroah-Hartman
parent 49b34bd3ad
commit 8aadc136d8
1 changed files with 17 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/9p/trans_rdma.c
+17 -2
View File
@@ -240,25 +240,36 @@ p9_cm_event_handler(struct rdma_cm_id *id, struct rdma_cm_event *event)
{
struct p9_client *c = id->context;
struct p9_trans_rdma *rdma = c->trans;
unsigned long flags;
switch (event->event) {
case RDMA_CM_EVENT_ADDR_RESOLVED:
spin_lock_irqsave(&rdma->req_lock, flags);
BUG_ON(rdma->state != P9_RDMA_INIT);
rdma->state = P9_RDMA_ADDR_RESOLVED;
spin_unlock_irqrestore(&rdma->req_lock, flags);
break;
case RDMA_CM_EVENT_ROUTE_RESOLVED:
spin_lock_irqsave(&rdma->req_lock, flags);
BUG_ON(rdma->state != P9_RDMA_ADDR_RESOLVED);
rdma->state = P9_RDMA_ROUTE_RESOLVED;
spin_unlock_irqrestore(&rdma->req_lock, flags);
break;
case RDMA_CM_EVENT_ESTABLISHED:
spin_lock_irqsave(&rdma->req_lock, flags);
BUG_ON(rdma->state != P9_RDMA_ROUTE_RESOLVED);
rdma->state = P9_RDMA_CONNECTED;
spin_unlock_irqrestore(&rdma->req_lock, flags);
break;
case RDMA_CM_EVENT_DISCONNECTED:
if (rdma)
if (rdma) {
spin_lock_irqsave(&rdma->req_lock, flags);
rdma->state = P9_RDMA_CLOSED;
spin_unlock_irqrestore(&rdma->req_lock, flags);
}
c->status = Disconnected;
break;
@@ -296,6 +307,7 @@ recv_done(struct ib_cq *cq, struct ib_wc *wc)
struct p9_req_t *req;
int err = 0;
int16_t tag;
unsigned long flags;
req = NULL;
ib_dma_unmap_single(rdma->cm_id->device, c->busa, client->msize,
@@ -332,7 +344,10 @@ recv_done(struct ib_cq *cq, struct ib_wc *wc)
err_out:
p9_debug(P9_DEBUG_ERROR, "req %p err %d status %d\n",
req, err, wc->status);
rdma->state = P9_RDMA_FLUSHING;
spin_lock_irqsave(&rdma->req_lock, flags);
if (rdma->state < P9_RDMA_FLUSHING)
rdma->state = P9_RDMA_FLUSHING;
spin_unlock_irqrestore(&rdma->req_lock, flags);
client->status = Disconnected;
goto out;
}