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[34.127.51.67]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39e554e5529sm6677054a91.4.2026.09.20.22.27.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 20 Sep 2026 22:27:04 -0700 (PDT) From: Hui Peng To: bhelgaas@google.com, airlied@redhat.com Cc: benh@kernel.crashing.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, benquike@gmail.com Subject: [PATCH v2 1/2] PCI/VGA: fix inverted vga_tryget() return check in vga_arb_write() Date: Mon, 21 Sep 2026 05:27:01 +0000 Message-ID: <20260921052702.1725696-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog In-Reply-To: <20260919222629.3798073-1-benquike@gmail.com> References: <20260919222629.3798073-1-benquike@gmail.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In vga_arb_write(), the "trylock" command handler calls vga_tryget(pdev, io_state) and checks: if (vga_tryget(pdev, io_state)) { /* Update the client's locks lists... */ However, vga_tryget() returns 0 on success and a negative errno (-EBUSY) when the VGA resources are already locked. Because the check tests for a non-zero return value, a successful vga_tryget() skips incrementing priv->cards[i].io_cnt / mem_cnt and skips reporting success, leaking the acquired VGA lock, whereas a failed vga_tryget() (-EBUSY) erroneously records the lock in priv->cards[i] so a subsequent "unlock" or file release decrements the lock count without holding the lock. Check if (vga_tryget(pdev, io_state) == 0) in vga_arb_write(). Tested in QEMU against Linux 7.3.0-rc3 by opening /dev/vga_arbiter and writing "trylock io+mem" followed by closing the file descriptor. On the unfixed kernel, write("trylock io+mem") acquires the VGA lock (locks=io+mem(1:1)) but takes the error branch and returns -EBUSY (-16) without recording the lock in priv->cards[], permanently leaking the lock on close(); with this patch applied, write("trylock io+mem") succeeds (ret = 14) and close() cleanly releases the lock (locks=none(0:0)). Fixes: deb2d2ecd43d ("PCI/GPU: implement VGA arbitration on Linux") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Hui Peng --- Changes in v2: - Split the vga_tryget() return check fix in vga_arb_write() from the PCI_INVALID_CARD hot-unplug cleanup fix into a 2-patch series, and fix the commit message to reference vga_arb_write(), as noted by Sashiko. - Update Fixes: tag from the file-move commit 1d38fe6ee6a8 to deb2d2ecd43d ("PCI/GPU: implement VGA arbitration on Linux"). drivers/pci/vgaarb.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c index 3de05aee7859..350ab9624eb9 100644 --- a/drivers/pci/vgaarb.c +++ b/drivers/pci/vgaarb.c @@ -1272,7 +1272,7 @@ static ssize_t vga_arb_write(struct file *file, const char __user *buf, goto done; } - if (vga_tryget(pdev, io_state)) { + if (vga_tryget(pdev, io_state) == 0) { /* Update the client's locks lists... */ for (i = 0; i < MAX_USER_CARDS; i++) { if (priv->cards[i].pdev == pdev) { -- 2.49.0