dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds

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/<name> remains open. No UAPI or heap-driver interface change. [1] https://lore.kernel.org/dri-devel/175e98de-f414-47d7-81c1-c0fe0a8f7f62@amd.com/

Baineng Shou committed 2 months ago

Commit 30d0aff1 parent cb732d03 files · +61 −40Browse files

Unified · Split

3 files

drivers/dma-buf/dma-buf.c +20 −0
drivers/dma-buf/dma-heap.c +40 −40
include/linux/dma-buf.h +1 −0

drivers/dma-buf/dma-buf.c+20−0

@@ -803,6 +803,26 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) · 802 unmodified lines
803	803	}
804	804	EXPORT_SYMBOL_NS_GPL(dma_buf_fd, "DMA_BUF");
805	805
	806	+/**
	807	+ * dma_buf_fd_install - install a reserved fd for a dma-buf
	808	+ * @dmabuf: [in] pointer to dma_buf
	809	+ * @fd: [in] fd reserved with get_unused_fd_flags()
	810	+ *
	811	+ * Publishes a previously reserved fd into the caller's fd table.
	812	+ * Must only be called after all fallible work (e.g. copy_to_user)
	813	+ * has succeeded, as it cannot be undone safely once called.
	814	+ *
	815	+ * The caller is responsible for having emitted the trace event
	816	+ * (via dma_buf_fd() or get_unused_fd_flags() + this function)
	817	+ * before calling this.
	818	+ */
	819	+void dma_buf_fd_install(struct dma_buf *dmabuf, int fd)
	820	+{
	821	+ DMA_BUF_TRACE(trace_dma_buf_fd, dmabuf, fd);
	822	+ fd_install(fd, dmabuf->file);
	823	+}
	824	+EXPORT_SYMBOL_NS_GPL(dma_buf_fd_install, "DMA_BUF");
	825	+
806	826	/**
807	827	* dma_buf_get - returns the struct dma_buf related to an fd
808	828	* @fd: [in] fd associated with the struct dma_buf to be returned

drivers/dma-buf/dma-heap.c+40−40

@@ -55,33 +55,6 @@ MODULE_PARM_DESC(mem_accounting, · 54 unmodified lines
55	55	"Enable cgroup-based memory accounting for dma-buf heap allocations (default=false).");
56	56	EXPORT_SYMBOL_NS_GPL(mem_accounting, "DMA_BUF_HEAP");
57	57
58		−static int dma_heap_buffer_alloc(struct dma_heap *heap, size_t len,
59		− u32 fd_flags,
60		− u64 heap_flags)
61		−{
62		− struct dma_buf *dmabuf;
63		− int fd;
64		−
65		− /*
66		− * Allocations from all heaps have to begin
67		− * and end on page boundaries.
68		− */
69		− len = PAGE_ALIGN(len);
70		− if (!len)
71		− return -EINVAL;
72		−
73		− dmabuf = heap->ops->allocate(heap, len, fd_flags, heap_flags);
74		− if (IS_ERR(dmabuf))
75		− return PTR_ERR(dmabuf);
76		−
77		− fd = dma_buf_fd(dmabuf, fd_flags);
78		− if (fd < 0) {
79		− dma_buf_put(dmabuf);
80		− /* just return, as put will call release and that will free */
81		− }
82		− return fd;
83		−}
84		−
85	58	static int dma_heap_open(struct inode inode, struct file file)
86	59	{
87	60	struct dma_heap *heap;
@@ -99,30 +72,42 @@ static int dma_heap_open(struct inode inode, struct file file) · 11 unmodified lines
99	72	return 0;
100	73	}
101	74
102		−static long dma_heap_ioctl_allocate(struct file file, void data)
	75	+static struct dma_buf dma_heap_ioctl_allocate(struct file file, void *data)
103	76	{
104	77	struct dma_heap_allocation_data *heap_allocation = data;
105	78	struct dma_heap *heap = file->private_data;
	79	+ struct dma_buf *dmabuf;
106	80	int fd;
	81	+ size_t len;
107	82
108	83	if (heap_allocation->fd)
109		− return -EINVAL;
	84	+ return ERR_PTR(-EINVAL);
110	85
111	86	if (heap_allocation->fd_flags & ~DMA_HEAP_VALID_FD_FLAGS)
112		− return -EINVAL;
	87	+ return ERR_PTR(-EINVAL);
113	88
114	89	if (heap_allocation->heap_flags & ~DMA_HEAP_VALID_HEAP_FLAGS)
115		− return -EINVAL;
	90	+ return ERR_PTR(-EINVAL);
	91	+
	92	+ len = PAGE_ALIGN(heap_allocation->len);
	93	+ if (!len)
	94	+ return ERR_PTR(-EINVAL);
	95	+
	96	+ dmabuf = heap->ops->allocate(heap, len, heap_allocation->fd_flags,
	97	+ heap_allocation->heap_flags);
116	98
117		− fd = dma_heap_buffer_alloc(heap, heap_allocation->len,
118		− heap_allocation->fd_flags,
119		− heap_allocation->heap_flags);
120		− if (fd < 0)
121		− return fd;
	99	+ if (IS_ERR(dmabuf))
	100	+ return dmabuf;
	101	+
	102	+ fd = get_unused_fd_flags(heap_allocation->fd_flags);
	103	+ if (fd < 0) {
	104	+ dma_buf_put(dmabuf);
	105	+ return ERR_PTR(fd);
	106	+ }
122	107
123	108	heap_allocation->fd = fd;
124	109
125		− return 0;
	110	+ return dmabuf;
126	111	}
127	112
128	113	static unsigned int dma_heap_ioctl_cmds[] = {
@@ -138,6 +123,8 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd, · 9 unmodified lines
138	123	unsigned int in_size, out_size, drv_size, ksize;
139	124	int nr = _IOC_NR(ucmd);
140	125	int ret = 0;
	126	+ int fd;
	127	+ struct dma_buf *dmabuf;
141	128
142	129	if (nr >= ARRAY_SIZE(dma_heap_ioctl_cmds))
143	130	return -EINVAL;
@@ -174,15 +161,28 @@ static long dma_heap_ioctl(struct file *file, unsigned int ucmd, · 30 unmodified lines
174	161
175	162	switch (kcmd) {
176	163	case DMA_HEAP_IOCTL_ALLOC:
177		− ret = dma_heap_ioctl_allocate(file, kdata);
	164	+ dmabuf = dma_heap_ioctl_allocate(file, kdata);
	165	+
	166	+ if (IS_ERR(dmabuf)) {
	167	+ ret = PTR_ERR(dmabuf);
	168	+ break;
	169	+ }
	170	+
	171	+ fd = ((struct dma_heap_allocation_data *)kdata)->fd;
	172	+ if (copy_to_user((void __user *)arg, kdata, out_size) != 0) {
	173	+ put_unused_fd(fd);
	174	+ dma_buf_put(dmabuf);
	175	+ ret = -EFAULT;
	176	+ } else {
	177	+ dma_buf_fd_install(dmabuf, fd);
	178	+ }
	179	+
178	180	break;
179	181	default:
180	182	ret = -ENOTTY;
181	183	goto err;
182	184	}
183	185
184		− if (copy_to_user((void __user *)arg, kdata, out_size) != 0)
185		− ret = -EFAULT;
186	186	err:
187	187	if (kdata != stack_kdata)
188	188	kfree(kdata);

include/linux/dma-buf.h+1−0

@@ -567,6 +567,7 @@ void dma_buf_unpin(struct dma_buf_attachment *attach); · 566 unmodified lines
567	567	struct dma_buf dma_buf_export(const struct dma_buf_export_info exp_info);
568	568
569	569	int dma_buf_fd(struct dma_buf *dmabuf, int flags);
	570	+void dma_buf_fd_install(struct dma_buf *dmabuf, int fd);
570	571	struct dma_buf *dma_buf_get(int fd);
571	572	void dma_buf_put(struct dma_buf *dmabuf);
572	573