| Message ID | 20210714071144.62126-1-guangming.cao@mediatek.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | dma-buf: add kernel count for dma_buf | expand |
Am 14.07.21 um 09:11 schrieb guangming.cao@mediatek.com: > From: Guangming Cao <Guangming.Cao@mediatek.com> > > Add a refcount for kernel to prevent UAF(Use After Free) issue. Well NAK on so many levels. > > We can assume a case like below: > 1. kernel space alloc dma_buf(file count = 1) > 2. kernel use dma_buf to get fd(file count = 1) > 3. userspace use fd to do mapping (file count = 2) Creating an userspace mapping increases the reference count for the underlying file object. See the implementation of mmap_region(): ... vma->vm_file = get_file(file); error = call_mmap(file, vma); ... What can happen is the the underlying exporter redirects the mmap to a different file, e.g. TTM or GEM drivers do that all the time. But this is fine since then the VA mapping is independent of the DMA-buf. > 4. kernel call dma_buf_put (file count = 1) > 5. userpsace close buffer fd(file count = 0) > 6. at this time, buffer is released, but va is valid!! > So we still can read/write buffer via mmap va, > it maybe cause memory leak, or kernel exception. > And also, if we use "ls -ll" to watch corresponding process > fd link info, it also will cause kernel exception. > > Another case: > Using dma_buf_fd to generate more than 1 fd, because > dma_buf_fd will not increase file count, thus, when close > the second fd, it maybe occurs error. Each opened fd will increase the reference count so this is certainly not correct what you describe here. Regards, Christian. > > Solution: > Add a kernel count for dma_buf, and make sure the file count > of dma_buf.file hold by kernel is 1. > > Notes: For this solution, kref couldn't work because kernel ref > maybe added from 0, but kref don't allow it. > > Signed-off-by: Guangming Cao <Guangming.Cao@mediatek.com> > --- > drivers/dma-buf/dma-buf.c | 23 +++++++++++++++++++---- > include/linux/dma-buf.h | 6 ++++-- > 2 files changed, 23 insertions(+), 6 deletions(-) > > diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c > index 511fe0d217a0..04ee92aac8b9 100644 > --- a/drivers/dma-buf/dma-buf.c > +++ b/drivers/dma-buf/dma-buf.c > @@ -62,6 +62,7 @@ static void dma_buf_release(struct dentry *dentry) > if (unlikely(!dmabuf)) > return; > > + WARN_ON(atomic64_read(&dmabuf->kernel_ref)); > BUG_ON(dmabuf->vmapping_counter); > > /* > @@ -555,6 +556,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) > goto err_module; > } > > + atomic64_set(&dmabuf->kernel_ref, 1); > dmabuf->priv = exp_info->priv; > dmabuf->ops = exp_info->ops; > dmabuf->size = exp_info->size; > @@ -617,6 +619,9 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) > > fd_install(fd, dmabuf->file); > > + /* Add file cnt for each new fd */ > + get_file(dmabuf->file); > + > return fd; > } > EXPORT_SYMBOL_GPL(dma_buf_fd); > @@ -626,12 +631,13 @@ EXPORT_SYMBOL_GPL(dma_buf_fd); > * @fd: [in] fd associated with the struct dma_buf to be returned > * > * On success, returns the struct dma_buf associated with an fd; uses > - * file's refcounting done by fget to increase refcount. returns ERR_PTR > - * otherwise. > + * dmabuf's ref refcounting done by kref_get to increase refcount. > + * Returns ERR_PTR otherwise. > */ > struct dma_buf *dma_buf_get(int fd) > { > struct file *file; > + struct dma_buf *dmabuf; > > file = fget(fd); > > @@ -643,7 +649,12 @@ struct dma_buf *dma_buf_get(int fd) > return ERR_PTR(-EINVAL); > } > > - return file->private_data; > + dmabuf = file->private_data; > + /* replace file count increase as ref increase for kernel user */ > + get_dma_buf(dmabuf); > + fput(file); > + > + return dmabuf; > } > EXPORT_SYMBOL_GPL(dma_buf_get); > > @@ -662,7 +673,11 @@ void dma_buf_put(struct dma_buf *dmabuf) > if (WARN_ON(!dmabuf || !dmabuf->file)) > return; > > - fput(dmabuf->file); > + if (WARN_ON(!atomic64_read(&dmabuf->kernel_ref))) > + return; > + > + if (!atomic64_dec_return(&dmabuf->kernel_ref)) > + fput(dmabuf->file); > } > EXPORT_SYMBOL_GPL(dma_buf_put); > > diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h > index efdc56b9d95f..bc790cb028eb 100644 > --- a/include/linux/dma-buf.h > +++ b/include/linux/dma-buf.h > @@ -308,6 +308,7 @@ struct dma_buf_ops { > struct dma_buf { > size_t size; > struct file *file; > + atomic64_t kernel_ref; > struct list_head attachments; > const struct dma_buf_ops *ops; > struct mutex lock; > @@ -436,7 +437,7 @@ struct dma_buf_export_info { > .owner = THIS_MODULE } > > /** > - * get_dma_buf - convenience wrapper for get_file. > + * get_dma_buf - increase a kernel ref of dma-buf > * @dmabuf: [in] pointer to dma_buf > * > * Increments the reference count on the dma-buf, needed in case of drivers > @@ -446,7 +447,8 @@ struct dma_buf_export_info { > */ > static inline void get_dma_buf(struct dma_buf *dmabuf) > { > - get_file(dmabuf->file); > + if (atomic64_inc_return(&dmabuf->kernel_ref) == 1) > + get_file(dmabuf->file); > } > > /**
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index 511fe0d217a0..04ee92aac8b9 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -62,6 +62,7 @@ static void dma_buf_release(struct dentry *dentry) if (unlikely(!dmabuf)) return; + WARN_ON(atomic64_read(&dmabuf->kernel_ref)); BUG_ON(dmabuf->vmapping_counter); /* @@ -555,6 +556,7 @@ struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info) goto err_module; } + atomic64_set(&dmabuf->kernel_ref, 1); dmabuf->priv = exp_info->priv; dmabuf->ops = exp_info->ops; dmabuf->size = exp_info->size; @@ -617,6 +619,9 @@ int dma_buf_fd(struct dma_buf *dmabuf, int flags) fd_install(fd, dmabuf->file); + /* Add file cnt for each new fd */ + get_file(dmabuf->file); + return fd; } EXPORT_SYMBOL_GPL(dma_buf_fd); @@ -626,12 +631,13 @@ EXPORT_SYMBOL_GPL(dma_buf_fd); * @fd: [in] fd associated with the struct dma_buf to be returned * * On success, returns the struct dma_buf associated with an fd; uses - * file's refcounting done by fget to increase refcount. returns ERR_PTR - * otherwise. + * dmabuf's ref refcounting done by kref_get to increase refcount. + * Returns ERR_PTR otherwise. */ struct dma_buf *dma_buf_get(int fd) { struct file *file; + struct dma_buf *dmabuf; file = fget(fd); @@ -643,7 +649,12 @@ struct dma_buf *dma_buf_get(int fd) return ERR_PTR(-EINVAL); } - return file->private_data; + dmabuf = file->private_data; + /* replace file count increase as ref increase for kernel user */ + get_dma_buf(dmabuf); + fput(file); + + return dmabuf; } EXPORT_SYMBOL_GPL(dma_buf_get); @@ -662,7 +673,11 @@ void dma_buf_put(struct dma_buf *dmabuf) if (WARN_ON(!dmabuf || !dmabuf->file)) return; - fput(dmabuf->file); + if (WARN_ON(!atomic64_read(&dmabuf->kernel_ref))) + return; + + if (!atomic64_dec_return(&dmabuf->kernel_ref)) + fput(dmabuf->file); } EXPORT_SYMBOL_GPL(dma_buf_put); diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h index efdc56b9d95f..bc790cb028eb 100644 --- a/include/linux/dma-buf.h +++ b/include/linux/dma-buf.h @@ -308,6 +308,7 @@ struct dma_buf_ops { struct dma_buf { size_t size; struct file *file; + atomic64_t kernel_ref; struct list_head attachments; const struct dma_buf_ops *ops; struct mutex lock; @@ -436,7 +437,7 @@ struct dma_buf_export_info { .owner = THIS_MODULE } /** - * get_dma_buf - convenience wrapper for get_file. + * get_dma_buf - increase a kernel ref of dma-buf * @dmabuf: [in] pointer to dma_buf * * Increments the reference count on the dma-buf, needed in case of drivers @@ -446,7 +447,8 @@ struct dma_buf_export_info { */ static inline void get_dma_buf(struct dma_buf *dmabuf) { - get_file(dmabuf->file); + if (atomic64_inc_return(&dmabuf->kernel_ref) == 1) + get_file(dmabuf->file); } /**