From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f169.google.com (mail-pg1-f169.google.com [209.85.215.169]) (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 5EE1F322B8F for ; Mon, 17 Aug 2026 05:05:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.169 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786943116; cv=none; b=McX25lz8rsoDa+O7Rj+mV7bW/8gZ2Pxwxj3BogbbitM9e3iO/oiQtOoI714DZW98EGgcH+AX0egX/Tw+MwX9bNq1T6e66cy4gi5b5t9qhW7+sEvla5em0iYX8XQmIG01OqFhhYDHvjgFnxg5BXT7YxtyI86ukCEEjpJOz4W8c9M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786943116; c=relaxed/simple; bh=KsN2NJemOVK+q8gWtoYQXOOV0uMG84DgAIswe9hxUCk=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version:Content-Type; b=GDcU+1036fiHDylFWBB1SN2azNA5KYFG+Oa7v3FPLyNCJPmTgo3y45nsbihm+fd1laeLMYMxtahVhILd59vcqofwoXkyigoIi8bOqQF0mruycEtq68ozFJ/fYs5Xt1ZVa50k/XVJeYfxwZzHyQFaOIfnxhURFOg6rZjjwjWGhKk= 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=aIjxrcsC; arc=none smtp.client-ip=209.85.215.169 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="aIjxrcsC" Received: by mail-pg1-f169.google.com with SMTP id 41be03b00d2f7-ca97d139d5fso2459793a12.0 for ; Sun, 16 Aug 2026 22:05:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1786943114; x=1787547914; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=iopxSAPngaesoWpELP4kESRIlD5BFKpXn69XPl76vs4=; b=aIjxrcsCEliYLnoWcxqcgO32XWgY4kZOC1+3krERYQnZMpr6iuURZ6nyzmvJkQMWJq IoAxzIot6BjOnqN1A17EG1WOZ4Ty+rbLTbPl5IUL43FkUwRCqL0tZMUT72JaQq+C0ELq H4RgMjWg8RTpwS/JMWAu3/ShMgWjJ5bhYzlzGYPdyi5Fb+7Asco3398Xw7gNCl/y2DP5 KMt5uKZ1JVQ/OzArFC3Vm6eh/3kGab1xcbn0q6bRUKlH8sTdu8X8D1mRqwlthewIx3Gm WgYbev3kuHs3pOT0jp+LvA6E/pGQYtwK6AbaHkyAk4O9a7pyasGLKjbaHqK2q0dS36DK Uclw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786943114; x=1787547914; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:date:subject:cc:to:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=iopxSAPngaesoWpELP4kESRIlD5BFKpXn69XPl76vs4=; b=dDSh3ivw6639XJ6weliGVtERCyEIvyN6Vp/Js9dc/4vB86rV7VzbnkIovYecAFfZ6F aI/nWfewULDUMW4JyokQioaJGB0wEAih97EvVp4vzu4u1xxWdvXnkvuGVryOZ4rbWMmE A/Np26jPlu92e0WwQtMvKwfNKfutNaWen1+uTx3eC9WE3jIxhd/Bd8JjmdEB0UnmNEH0 0JVv6fdF0BtnPmtK54XxrJQHjv7mihuILc1yQ/9l4+dbgXOwvL0EHl0D0GlnwYHPHCoP hCb7GlCUoLy8zNHcq+ZXBeNisgmfk1ni30rLXSD0OInlP8TEgVvmJAZzBx+oLi1jEL9z iQ/A== X-Forwarded-Encrypted: i=1; AHgh+RqDswlTTxHmK4gbsUqQts7O6ZohXcRrl+LM20B5B/Objml+j39dsqpwlljZ1uiRwRi8uLX+mioFRcFFvg==@vger.kernel.org X-Gm-Message-State: AOJu0YxXlxjfq+PprjA7QPhKizBOoA1iPWCLF+q5W7ycfnmaCkDQC0fL i+L5ares4Ku58dx9qC2MgJY0pTlxNSc3739GkpCFXhBPbGEAJJ2E558G X-Gm-Gg: AR+sD12zwTHrUY5PDtPtkl8M1dIxg27r7xAfs+6oC/TR2PMIPsaRlghalpcIyPlScWM v1fGJgTCD3wwDGzqfZZLLoKsgxk7MUO6T1sm0MRZBFyQFKzNDXryghO11DlCmbJLYlvgqMIeRR9 VMkD1OlFl6vZ05DPOe1ng08u5+CDoICMEFB4hXdcfc1URKUj+KH8O9g96v5afRZldFdrCf6mul5 kohntWgIXjnl+kfyg1erOIDuTb5x8YeWLa3z6dO8wTJKLz7uQTeqcnIKnSFqFSAPXRtxvuZO8Kg F0H2Ev61pg0jRhPwwfIMlBCPqz8n+rqQh7Aclx8u2jxdkwK4LhvlGa5EXPJqB9s6cfobdnWC2dN aLK9Nsw7o2JFtuMKZTn+d2Aope4S55VQzc9lIq2CaiUBHCzV5+eE6JzV0hAk9zFGezrLAUKRXpU U7jcOUSJH/b6mZe8Ec4ZHn7J+c9D4ZvAMFwlnu0+J1C1R8EQCFEgFXZPtVIklcsMu/ X-Received: by 2002:a05:6a00:3699:b0:846:bc60:5bf7 with SMTP id d2e1a72fcca58-84fddf9180cmr25131878b3a.6.1786943113562; Sun, 16 Aug 2026 22:05:13 -0700 (PDT) Received: from baineng-pc.. ([117.133.183.252]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8517d267310sm2131036b3a.53.2026.08.16.22.05.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 16 Aug 2026 22:05:13 -0700 (PDT) From: Baineng Shou To: Sumit Semwal , =?UTF-8?q?Christian=20K=C3=B6nig?= , "T . J . Mercier" , Benjamin Gaignard , Brian Starkey , John Stultz , Sandeep Patil , "Andrew F . Davis" , Srinivas Kandagatla , David Airlie , Simona Vetter Cc: stable@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, Baineng Shou Subject: [PATCH v7 1/4] dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds Date: Mon, 17 Aug 2026 13:04:54 +0800 Message-Id: <20260817050457.1005285-2-shoubaineng@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260817050457.1005285-1-shoubaineng@gmail.com> References: <20260817050457.1005285-1-shoubaineng@gmail.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit DMA_HEAP_IOCTL_ALLOC allocates a dma-buf and installs an fd into the caller's fd table via dma_buf_fd() -> fd_install() before dma_heap_ioctl() copies the result back to userspace. If the trailing copy_to_user() fails, userspace never learns the fd number, but the fd (and the underlying dma-buf reference) are already visible to other threads in the same process and are leaked for the lifetime of the process. The obvious "close it on the failure path" fix is unsafe: once fd_install() has run, another thread can already dup() the fd, send it via SCM_RIGHTS, or close() it and let its number be reused, so a subsequent close_fd() from the ioctl path can operate on an unrelated file. This was pointed out by Christian König on v1 [1]. Restructure the allocation path so that fd_install() is the last, unfailable step of a successful ioctl: 1. heap->ops->allocate() creates the dma_buf. 2. get_unused_fd_flags() reserves an fd number in the caller's fd table without publishing it, so no other thread can observe it. 3. copy_to_user() delivers the fd number to userspace; on failure the fd is returned with put_unused_fd() and the dma_buf reference is dropped with dma_buf_put(), leaving no user- visible state behind. 4. dma_buf_fd_install() publishes the fd and emits the trace_dma_buf_fd tracepoint -- from here on the ioctl cannot fail. A new dma_buf_fd_install() helper is introduced in dma-buf.c to wrap fd_install() together with the DMA_BUF_TRACE() call, preserving the export tracing that dma_buf_fd() provides. dma_heap_ioctl_allocate() is refactored to return the struct dma_buf * directly (returning ERR_PTR on failure) so the caller holds the dmabuf reference across steps 3 and 4. The failure at step 3 is easily reachable from userspace: pass a struct dma_heap_allocation_data that lives in a page whose protection is flipped to PROT_READ between copy_from_user() and copy_to_user() (e.g. via mprotect()). Before this change each such ioctl leaks one dmabuf fd; after it, the fd table is unchanged on failure and only /dev/dma_heap/ remains open. No UAPI or heap-driver interface change. [1] https://lore.kernel.org/dri-devel/175e98de-f414-47d7-81c1-c0fe0a8f7f62@amd.com/ Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework") Cc: stable@vger.kernel.org Reviewed-by: T.J. Mercier Acked-by: Christian König Acked-by: Sumit Semwal Signed-off-by: Baineng Shou --- drivers/dma-buf/dma-buf.c | 20 ++++++++++ drivers/dma-buf/dma-heap.c | 80 +++++++++++++++++++------------------- include/linux/dma-buf.h | 1 + 3 files changed, 61 insertions(+), 40 deletions(-) diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index d504c636dc29..4c9add51f9ef 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -803,6 +803,26 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) } EXPORT_SYMBOL_NS_GPL(dma_buf_fd, "DMA_BUF"); +/** + * dma_buf_fd_install - install a reserved fd for a dma-buf + * @dmabuf: [in] pointer to dma_buf + * @fd: [in] fd reserved with get_unused_fd_flags() + * + * Publishes a previously reserved fd into the caller's fd table. + * Must only be called after all fallible work (e.g. copy_to_user) + * has succeeded, as it cannot be undone safely once called. + * + * The caller is responsible for having emitted the trace event + * (via dma_buf_fd() or get_unused_fd_flags() + this function) + * before calling this. + */ +void dma_buf_fd_install(struct dma_buf *dmabuf, int fd) +{ + DMA_BUF_TRACE(trace_dma_buf_fd, dmabuf, fd); + fd_install(fd, dmabuf->file); +} +EXPORT_SYMBOL_NS_GPL(dma_buf_fd_install, "DMA_BUF"); + /** * dma_buf_get - returns the struct dma_buf related to an fd * @fd: [in] fd associated with the struct dma_buf to be returned diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c index a76bf3f8b071..43c32fb28313 100644 --- a/drivers/dma-buf/dma-heap.c +++ b/drivers/dma-buf/dma-heap.c @@ -55,33 +55,6 @@ MODULE_PARM_DESC(mem_accounting, "Enable cgroup-based memory accounting for dma-buf heap allocations (default=false)."); EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP"); -static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len, - u32 fd_flags, - u64 heap_flags) -{ - struct dma_buf *dmabuf; - int fd; - - /* - * Allocations from all heaps have to begin - * and end on page boundaries. - */ - len = PAGE_ALIGN(len); - if (!len) - return -EINVAL; - - dmabuf = heap->ops->allocate(heap, len, fd_flags, heap_flags); - if (IS_ERR(dmabuf)) - return PTR_ERR(dmabuf); - - fd = dma_buf_fd(dmabuf, fd_flags); - if (fd < 0) { - dma_buf_put(dmabuf); - /* just return, as put will call release and that will free */ - } - return fd; -} - static int dma_heap_open(struct inode *inode, struct file *file) { struct dma_heap *heap; @@ -99,30 +72,42 @@ static int dma_heap_open(struct inode *inode, struct file *file) return 0; } -static long dma_heap_ioctl_allocate(struct file *file, void *data) +static struct dma_buf *dma_heap_ioctl_allocate(struct file *file, void *data) { struct dma_heap_allocation_data *heap_allocation = data; struct dma_heap *heap = file->private_data; + struct dma_buf *dmabuf; int fd; + size_t len; if (heap_allocation->fd) - return -EINVAL; + return ERR_PTR(-EINVAL); if (heap_allocation->fd_flags & ~DMA_HEAP_VALID_FD_FLAGS) - return -EINVAL; + return ERR_PTR(-EINVAL); if (heap_allocation->heap_flags & ~DMA_HEAP_VALID_HEAP_FLAGS) - return -EINVAL; + return ERR_PTR(-EINVAL); + + len = PAGE_ALIGN(heap_allocation->len); + if (!len) + return ERR_PTR(-EINVAL); + + dmabuf = heap->ops->allocate(heap, len, heap_allocation->fd_flags, + heap_allocation->heap_flags); - fd = dma_heap_buffer_alloc(heap, heap_allocation->len, - heap_allocation->fd_flags, - heap_allocation->heap_flags); - if (fd < 0) - return fd; + if (IS_ERR(dmabuf)) + return dmabuf; + + fd = get_unused_fd_flags(heap_allocation->fd_flags); + if (fd < 0) { + dma_buf_put(dmabuf); + return ERR_PTR(fd); + } heap_allocation->fd = fd; - return 0; + return dmabuf; } static unsigned int dma_heap_ioctl_cmds[] = { @@ -138,6 +123,8 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd, unsigned int in_size, out_size, drv_size, ksize; int nr = _IOC_NR(ucmd); int ret = 0; + int fd; + struct dma_buf *dmabuf; if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds)) return -EINVAL; @@ -174,15 +161,28 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd, switch (kcmd) { case DMA_HEAP_IOCTL_ALLOC: - ret = dma_heap_ioctl_allocate(file, kdata); + dmabuf = dma_heap_ioctl_allocate(file, kdata); + + if (IS_ERR(dmabuf)) { + ret = PTR_ERR(dmabuf); + break; + } + + fd = ((struct dma_heap_allocation_data *)kdata)->fd; + if (copy_to_user((void __user *)arg, kdata, out_size) != 0) { + put_unused_fd(fd); + dma_buf_put(dmabuf); + ret = -EFAULT; + } else { + dma_buf_fd_install(dmabuf, fd); + } + break; default: ret = -ENOTTY; goto err; } - if (copy_to_user((void __user *)arg, kdata, out_size) != 0) - ret = -EFAULT; err: if (kdata != stack_kdata) kfree(kdata); diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index d1203da56fc5..d15b2b31d3c9 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -567,6 +567,7 @@ void dma_buf_unpin(struct dma_buf_attachment *attach); struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info); int dma_buf_fd(struct dma_buf *dmabuf, int flags); +void dma_buf_fd_install(struct dma_buf *dmabuf, int fd); struct dma_buf *dma_buf_get(int fd); void dma_buf_put(struct dma_buf *dmabuf); -- 2.34.1