dma-buf: Move dma_buf_release() from fops to dentry_ops (4ab59c3c) · Commits · 戴 / test

Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which happens if the dma_buf_release() is called while the userspace is accessing the dma_buf pseudo fs's dmabuffs_dname() in another process, and dma_buf_release() releases the dmabuf object when the last reference to the struct file goes away. I discussed with Arnd Bergmann, and he suggested that rather than tying the dma_buf_release() to the file_operations' release(), we can tie it to the dentry_operations' d_release(), which will be called when the last ref to the dentry is removed. The path exercised by __fput() calls f_op->release() first, and then calls dput, which eventually calls d_op->d_release(). In the 'normal' case, when no userspace access is happening via dma_buf pseudo fs, there should be exactly one fd, file, dentry and inode, so closing the fd will kill of everything right away. In the presented case, the dentry's d_release() will be called only when the dentry's last ref is released. Therefore, lets move dma_buf_release() from fops->release() to d_ops->d_release() Many thanks to Arnd for his FS insights :) [1]: https://lore.kernel.org/patchwork/patch/1238278/ Fixes: ("dma-buf: add DMA_BUF_SET_NAME ioctls") Reported-by:

<syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com> Cc: <stable@vger.kernel.org> [5.3+] Cc: Arnd Bergmann <arnd@arndb.de> Reported-by:

Charan Teja Reddy <charante@codeaurora.org> Reviewed-by:

Arnd Bergmann <arnd@arndb.de> Signed-off-by:

Sumit Semwal <sumit.semwal@linaro.org> Tested-by:

Charan Teja Reddy <charante@codeaurora.org> Link: https://patchwork.freedesktop.org/patch/msgid/20200611114418.19852-1-sumit.semwal@linaro.org

drivers/dma-buf/dma-buf.c

+25 −29

Original line number	Diff line number	Diff line
		@@ -54,37 +54,11 @@ static char dmabuffs_dname(struct dentry dentry, char *buffer, int buflen)
		dentry->d_name.name, ret > 0 ? name : "");
		}

		static const struct dentry_operations dma_buf_dentry_ops = {
		.d_dname = dmabuffs_dname,
		};

		static struct vfsmount *dma_buf_mnt;

		static int dma_buf_fs_init_context(struct fs_context *fc)
		{
		struct pseudo_fs_context *ctx;

		ctx = init_pseudo(fc, DMA_BUF_MAGIC);
		if (!ctx)
		return -ENOMEM;
		ctx->dops = &dma_buf_dentry_ops;
		return 0;
		}

		static struct file_system_type dma_buf_fs_type = {
		.name = "dmabuf",
		.init_fs_context = dma_buf_fs_init_context,
		.kill_sb = kill_anon_super,
		};

		static int dma_buf_release(struct inode inode, struct file file)
		static void dma_buf_release(struct dentry *dentry)
		{
		struct dma_buf *dmabuf;

		if (!is_dma_buf_file(file))
		return -EINVAL;

		dmabuf = file->private_data;
		dmabuf = dentry->d_fsdata;

		BUG_ON(dmabuf->vmapping_counter);

		@@ -110,9 +84,32 @@ static int dma_buf_release(struct inode inode, struct file file)
		module_put(dmabuf->owner);
		kfree(dmabuf->name);
		kfree(dmabuf);
		}

		static const struct dentry_operations dma_buf_dentry_ops = {
		.d_dname = dmabuffs_dname,
		.d_release = dma_buf_release,
		};

		static struct vfsmount *dma_buf_mnt;

		static int dma_buf_fs_init_context(struct fs_context *fc)
		{
		struct pseudo_fs_context *ctx;

		ctx = init_pseudo(fc, DMA_BUF_MAGIC);
		if (!ctx)
		return -ENOMEM;
		ctx->dops = &dma_buf_dentry_ops;
		return 0;
		}

		static struct file_system_type dma_buf_fs_type = {
		.name = "dmabuf",
		.init_fs_context = dma_buf_fs_init_context,
		.kill_sb = kill_anon_super,
		};

		static int dma_buf_mmap_internal(struct file file, struct vm_area_struct vma)
		{
		struct dma_buf *dmabuf;
		@@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file m, struct file file)
		}

		static const struct file_operations dma_buf_fops = {
		.release = dma_buf_release,
		.mmap = dma_buf_mmap_internal,
		.llseek = dma_buf_llseek,
		.poll = dma_buf_poll,

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