From f4cc21c6a8e9d392871477f9fd98d68e5ad80272 Mon Sep 17 00:00:00 2001 From: Norbert Szetei Date: Mon, 27 Jul 2026 10:06:12 +0200 Subject: [PATCH] RDMA/ucma: Lock the handler in ucma_write_cm_event() ctx->file may only be changed under the handler lock and the xa_lock, which is what stops uevents being queued for a ctx while ucma_migrate_id() moves it to another file. The CM core takes that lock before invoking ucma_event_handler(), but the write() paths that queue uevents themselves do not. ucma_write_cm_event() re-reads ctx->file for each of its four dereferences, so ucma_migrate_id() can swap it mid-sequence: mutex_lock(&ctx->file->mut); /* file A */ list_add_tail(&uevent->list, &ctx->file->event_list); /* file B */ mutex_unlock(&ctx->file->mut); /* file B */ wake_up_interruptible(&ctx->file->poll_wait); /* file B */ The window is the mutex_lock() itself: the writer sleeps in it while the migration reassigns ctx->file. The list_add_tail() then runs on file B's event_list holding only file A's mutex: list_add corruption. prev->next should be next (ffff888101320f30), but was ffff88814a08c418. (prev=ffff88814a075c18). kernel BUG at lib/list_debug.c:32! Call Trace: ucma_write_cm_event+0x36e/0x5e0 and file A's mut is left held forever, wedging its next writer in D state. The uevent is also stranded on a list ucma_cleanup_ctx_events() will not walk, so it outlives its context. /dev/infiniband/rdma_cm is 0666 and no RDMA device is involved, so an unprivileged user reaches all of this. Take the handler lock, as ucma_cleanup_mc_events() does; ctx->cm_id is pinned by the ucma_get_ctx() reference. Fixes: a3c9d0fcd371 ("RDMA/ucma: Support write an event into a CM") Link: https://patch.msgid.link/r/60544A67-EFD6-4D5D-974C-D983445F1070@doyensec.com Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Norbert Szetei Signed-off-by: Jason Gunthorpe --- drivers/infiniband/core/ucma.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c index 878561fa1cb5..a29f2d4b8d14 100644 --- a/drivers/infiniband/core/ucma.c +++ b/drivers/infiniband/core/ucma.c @@ -1776,6 +1776,13 @@ static ssize_t ucma_write_cm_event(struct ucma_file *file, goto out; } + rdma_lock_handler(ctx->cm_id); + if (!ctx->uid) { + kfree(uevent); + ret = -EINVAL; + goto err_unlock; + } + uevent->ctx = ctx; uevent->resp.uid = ctx->uid; uevent->resp.id = ctx->id; @@ -1789,6 +1796,8 @@ static ssize_t ucma_write_cm_event(struct ucma_file *file, mutex_unlock(&ctx->file->mut); wake_up_interruptible(&ctx->file->poll_wait); +err_unlock: + rdma_unlock_handler(ctx->cm_id); out: ucma_put_ctx(ctx); return ret;