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Sat, 30 May 2026 20:40:56 -0700 (PDT) Received: from KERNELXING-MC1.tencent.com ([2408:8207:1920:4670:4008:f5e4:8e02:25f0]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c85772b9591sm5968282a12.22.2026.05.30.20.40.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 30 May 2026 20:40:54 -0700 (PDT) From: Jason Xing To: nbd@nbd.name, lorenzo@kernel.org, ryder.lee@mediatek.com, shayne.chen@mediatek.com, sean.wang@mediatek.com, matthias.bgg@gmail.com, angelogioacchino.delregno@collabora.com, akpm@linux-foundation.org, axboe@kernel.dk Cc: linux-wireless@vger.kernel.org, Jason Xing Subject: [PATCH 2/3] wifi: mt76: mt7915: use relay_subbuf_avail() to fix stale fwlog reads Date: Sun, 31 May 2026 11:40:09 +0800 Message-Id: <20260531034010.85002-3-kerneljasonxing@gmail.com> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20260531034010.85002-1-kerneljasonxing@gmail.com> References: <20260531034010.85002-1-kerneljasonxing@gmail.com> Precedence: bulk X-Mailing-List: linux-wireless@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jason Xing relay_reserve() advances buf->offset before the caller writes data. Since relay_file_read() uses buf->offset as the readable upper bound of the active sub-buffer, a concurrent reader can observe the reserved-but-not-yet-written region, resulting in stale data. WRITER READER (active sub-buf) ------ ------ relay_reserve(4+L) buf->offset += 4+L ---+ *(u32*)dest = L | (offset already exposes the slot) +--> read(&len, 4) => L (VALID!) <> read(buf, L) => STALE data X memcpy(dest+4, ..., L) [payload written - too late] The userspace reader [1] uses poll() + read(&len, 4) + read(buf, len), which is racy against the relay_reserve() window described above. Switch to relay_subbuf_avail() + __relay_write() so the offset only advances after each chunk is copied. [1] https://github.com/openwrt/mt76/blob/master/tools/fwlog.c Fixes: 988845c9361a ("mt76: mt7915: add support for passing chip/firmware debug data to user space") Signed-off-by: Jason Xing --- .../wireless/mediatek/mt76/mt7915/debugfs.c | 27 +++++++++---------- 1 file changed, 13 insertions(+), 14 deletions(-) diff --git a/drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c b/drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c index 26ed3745af43..d564b265dc27 100644 --- a/drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c +++ b/drivers/net/wireless/mediatek/mt76/mt7915/debugfs.c @@ -1346,22 +1346,21 @@ mt7915_debugfs_write_fwlog(struct mt7915_dev *dev, const void *hdr, int hdrlen, { static DEFINE_SPINLOCK(lock); unsigned long flags; - void *dest; + u32 rec_len = len; + + if (hdr) + rec_len += hdrlen; spin_lock_irqsave(&lock, flags); - dest = relay_reserve(dev->relay_fwlog, hdrlen + len + 4); - if (dest) { - *(u32 *)dest = hdrlen + len; - dest += 4; - - if (hdrlen) { - memcpy(dest, hdr, hdrlen); - dest += hdrlen; - } - - memcpy(dest, data, len); - relay_flush(dev->relay_fwlog); - } + if (!relay_subbuf_avail(dev->relay_fwlog, sizeof(rec_len) + rec_len)) + goto out; + + __relay_write(dev->relay_fwlog, &rec_len, sizeof(rec_len)); + if (hdr) + __relay_write(dev->relay_fwlog, hdr, hdrlen); + __relay_write(dev->relay_fwlog, data, len); + relay_flush(dev->relay_fwlog); +out: spin_unlock_irqrestore(&lock, flags); } -- 2.43.7