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([117.133.183.252]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d022bc9bd4sm21059695ad.48.2026.07.29.23.26.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jul 2026 23:26:21 -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 v5 1/4] dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds Date: Thu, 30 Jul 2026 14:25:45 +0800 Message-Id: <20260730062548.231239-2-shoubaineng@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260730062548.231239-1-shoubaineng@gmail.com> References: <20260730062548.231239-1-shoubaineng@gmail.com> Precedence: bulk X-Mailing-List: stable@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 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