From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f43.google.com (mail-wm1-f43.google.com [209.85.128.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 40ECE343D8A for ; Wed, 18 Feb 2026 17:36:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.43 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771436207; cv=none; b=GacGTlAm/JR+jlvE0NkfaIGev8MGdggMQ3tTQlnNZXzk8+Q32Vl0spLa4UcR5udKH24in8uV8F1JKS/ic4ymOwwSRtt1KWo+Z+Lim9TZ7AxDBMSKZBVmQCleQsdKt4qrAbpvR6X/gJLETaejdYtFiGFIsvbLTLmQoL+S9IXKhRE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771436207; c=relaxed/simple; bh=ryk1XlFpYkbWCCRIEYCdmMdH4Bm5ivPc/TwrajVtluw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=KpMHBveTOY/K0iaW5HUb9u8rqTcxg9mcu6LVkiok4tarrTfP7J7Qgf41dW9M7NoYtgUGMSuTvJQ2njVnTmOMnCyVqgTqyVE1iWrBl4dy+dCqiwwLKq5fETpvRITzQTxXkcNVe/+LK04Q1F0zm41exqrd89nJvYHQbWZ8hfBP3vU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=fPfvwdiW; arc=none smtp.client-ip=209.85.128.43 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="fPfvwdiW" Received: by mail-wm1-f43.google.com with SMTP id 5b1f17b1804b1-480706554beso948635e9.1 for ; Wed, 18 Feb 2026 09:36:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1771436204; x=1772041004; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=opGeJXdqBNHSNGuTpufEOdqG+49HpE5DgTtWk7Ja0tg=; b=fPfvwdiWDb4Z/WTrRpEyjGKWx0uF+c3WWRdZpfUgGpmGf/wkqSJQDTsZfLyUtPb8bR 3j/uHqLognwuuARMvQKskx8S54cNDCrd9ueIKDN9vt8wb9SZdGdXR7oSoAbxaLMTjn8M wyTG6ibzHAQZNvaMN9zgUG1+h0oLkSFuF13NONi6yvCohPCC1NUIsTIDL6dpklApzzxh 99gjgu2i88SLjrIjNZCndX4iVqVBUcR8kMfPRBjin5emSni5dfRSi8JaVBvepj+BeksG +Yb0AUnaTtWu4svK6bkYXSMZER1LQU1gy5XI2j01f2/eP09DSQo9/YJ0g0kRstVAw0m4 XGQQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1771436204; x=1772041004; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-gg:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=opGeJXdqBNHSNGuTpufEOdqG+49HpE5DgTtWk7Ja0tg=; b=b/i+q6g7AIE+BxQ3yql0EloeWmhe8wClVqCkNlNdA4GpXxOEGV4C7cYI0+86QZimWf n4iq+HphZd/mtTzoOvAJseHDh7chIn2vOJS2jaB18NvrEPZJA+n5whOsYRTktuOw1tv2 aROD72dAwrfyPyqxMDmrH4ibiDuAgBRJVv18iSMqQmquwp+gDaN81zJPtZ2p9uliqOdJ IrZMIQQWWQPfr+W1YjpsdEzMUJ5kZs+bSg3CQ+AyDoE1RXG9K68ogKnuEQ1XjHyqTrKn HYYIpAQY4b5oFEAANPgtNOD7tdSxjHcIe4NWUAshNTr4QEwI/zLuPuTeYog+tF4liOyv 6CMw== X-Gm-Message-State: AOJu0Yz44sLA4D+VZ7t8RZWm8nsp6iFibyVmgc+04PaJoIZFAeu0bXz6 Z/COk7k2hQcCNvxmwK7+nO17tBJA7ZYcNvBQJoEfsEv1lapiqpwfevWSWOvQTpgN X-Gm-Gg: AZuq6aI9WScNDgT3PMaY3oS4szziSdh47ZtvTxdMXMeQdKzJjtxfuC2RdQvQNy0TL9p PveXBgYJYbyeWRpDw0KZ1EtkUbgck11KnGmUTgT5C6zEtXGRcAhxgGNpW3d73M4UgCQ+KLCPbFk oetuku/vNwizVaqVE46SSspoa/PLidKZTjT/WYr1ust4aifr8eSH4vT6/B4ubj+ItBIRf+NztIP zvF0qeKP1URTbu2VRdSK2FjkBpQ5/v8pSVAd2FHV8y/L78U7GH4/Ujod1Z9k0Ls+kE8EvBWMx6j Wt1cA3dd4CM46HChhwW/g1XLwzS5QV0qnAK5QIe9NQ514Tc4CEiVEkwDC8pgTJmf5uSR5HgfCgN hKQnAPNKCrT9BtHsTsKKGEWWhDkUXUyjhbOVxLrn3klBZUiLDWyLPeG+1YRH10cwj5Fa/0gS2vZ uChHYmFF4UfyEP6Wl5sSHTstfNkJhNWCQfoaJUpNMmUYmMsm3mqygb5ehzHUlPunuaS7cHCTxmb oDzP+dEn1yws6yV59M7Ptl3a5mKg1TmmSkfxoIf X-Received: by 2002:a05:600c:5308:b0:47e:e946:3a72 with SMTP id 5b1f17b1804b1-48379bf78f1mr246397705e9.27.1771436204063; Wed, 18 Feb 2026 09:36:44 -0800 (PST) Received: from 127.mynet ([2a01:4b00:bd21:4f00:7cc6:d3ca:494:116c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4835d99e194sm464119405e9.8.2026.02.18.09.36.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Feb 2026 09:36:43 -0800 (PST) From: Pavel Begunkov To: io-uring@vger.kernel.org Cc: asml.silence@gmail.com, axboe@kernel.dk, netdev@vger.kernel.org, Kai Aizen Subject: [PATCH 1/1] io_uring/zcrx: fix user_ref race between scrub and refill paths Date: Wed, 18 Feb 2026 17:36:41 +0000 Message-ID: <364c2e7d4f53b26bb3133cfc4271183fcd450be2.1771435883.git.asml.silence@gmail.com> X-Mailer: git-send-email 2.52.0 Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kai Aizen The io_zcrx_put_niov_uref() function uses a non-atomic check-then-decrement pattern (atomic_read followed by separate atomic_dec) to manipulate user_refs. This is serialized against other callers by rq_lock, but io_zcrx_scrub() modifies the same counter with atomic_xchg() WITHOUT holding rq_lock. On SMP systems, the following race exists: CPU0 (refill, holds rq_lock) CPU1 (scrub, no rq_lock) put_niov_uref: atomic_read(uref) - 1 // window opens atomic_xchg(uref, 0) - 1 return_niov_freelist(niov) [PUSH #1] // window closes atomic_dec(uref) - wraps to -1 returns true return_niov(niov) return_niov_freelist(niov) [PUSH #2: DOUBLE-FREE] The same niov is pushed to the freelist twice, causing free_count to exceed nr_iovs. Subsequent freelist pushes then perform an out-of-bounds write (a u32 value) past the kvmalloc'd freelist array into the adjacent slab object. Fix this by replacing the non-atomic read-then-dec in io_zcrx_put_niov_uref() with an atomic_try_cmpxchg loop that atomically tests and decrements user_refs. This makes the operation safe against concurrent atomic_xchg from scrub without requiring scrub to acquire rq_lock. Fixes: 34a3e60821ab ("io_uring/zcrx: implement zerocopy receive pp memory provider") Cc: stable@vger.kernel.org Signed-off-by: Kai Aizen [pavel: removed a warning and a comment] Signed-off-by: Pavel Begunkov --- io_uring/zcrx.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c index 3d377523ff7e..0c9bf540b12b 100644 --- a/io_uring/zcrx.c +++ b/io_uring/zcrx.c @@ -341,10 +341,14 @@ static inline atomic_t *io_get_user_counter(struct net_iov *niov) static bool io_zcrx_put_niov_uref(struct net_iov *niov) { atomic_t *uref = io_get_user_counter(niov); + int old; + + old = atomic_read(uref); + do { + if (unlikely(old == 0)) + return false; + } while (!atomic_try_cmpxchg(uref, &old, old - 1)); - if (unlikely(!atomic_read(uref))) - return false; - atomic_dec(uref); return true; } -- 2.52.0