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The abnormal client death on the DSP side triggers a glink channel teardown which propagates up through the rpmsg bus and calls fastrpc_rpmsg_remove(). fastrpc_rpmsg_remove() nulls cctx->rpdev before calling misc_deregister(). If a concurrent open() enters fastrpc_device_open() in this window and fastrpc_session_alloc() returns NULL (sessions exhausted by the leaked slot), the error path dereferences cctx->rpdev->dev causing a NULL pointer dereference: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 pc : fastrpc_device_open+0x1b8/0x258 [fastrpc] Call trace: fastrpc_device_open+0x1b8/0x258 [fastrpc] (P) misc_open+0xd8/0x1a0 Fix by moving misc_deregister() before rpdev = NULL. misc_open() and misc_deregister() both take misc_mtx, so misc_deregister() will either block until fastrpc_device_open() completes or prevent new opens from entering it entirely. Fixes: 7c11df42d0c7 ("misc: fastrpc: Fix device_open when no session is available") Cc: stable@vger.kernel.org Reviewed-by: Ekansh Gupta Signed-off-by: Vinayak Katoch --- drivers/misc/fastrpc.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c index 5dd1990d3e2a..f280bff2edf0 100644 --- a/drivers/misc/fastrpc.c +++ b/drivers/misc/fastrpc.c @@ -2697,6 +2697,12 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev) struct fastrpc_user *user; unsigned long flags; + if (cctx->fdevice) + misc_deregister(&cctx->fdevice->miscdev); + + if (cctx->secure_fdevice) + misc_deregister(&cctx->secure_fdevice->miscdev); + /* No invocations past this point */ spin_lock_irqsave(&cctx->lock, flags); cctx->rpdev = NULL; @@ -2704,12 +2710,6 @@ static void fastrpc_rpmsg_remove(struct rpmsg_device *rpdev) fastrpc_notify_users(user); spin_unlock_irqrestore(&cctx->lock, flags); - if (cctx->fdevice) - misc_deregister(&cctx->fdevice->miscdev); - - if (cctx->secure_fdevice) - misc_deregister(&cctx->secure_fdevice->miscdev); - list_for_each_entry_safe(buf, b, &cctx->invoke_interrupted_mmaps, node) list_del(&buf->node); -- 2.34.1