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[109.152.100.164]) by smtp.gmail.com with ESMTPSA id k190sm11621745wme.33.2020.10.09.05.31.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 09 Oct 2020 05:31:36 -0700 (PDT) To: Matthew Wilcox Cc: syzbot , axboe@kernel.dk, io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk References: <0000000000001a684d05b1385e71@google.com> <3a98a77a-a507-954a-f2ec-e38af18c168f@gmail.com> <20201009121211.GQ20115@casper.infradead.org> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Subject: Re: KASAN: use-after-free Read in __io_uring_files_cancel Message-ID: <6da35bc9-d072-c18b-2268-15d37fa786df@gmail.com> Date: Fri, 9 Oct 2020 15:28:54 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <20201009121211.GQ20115@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 09/10/2020 15:12, Matthew Wilcox wrote: > On Fri, Oct 09, 2020 at 02:10:49PM +0300, Pavel Begunkov wrote: >>> kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562 >>> xas_next_entry include/linux/xarray.h:1630 [inline] >>> __io_uring_files_cancel+0x417/0x440 fs/io_uring.c:8681 >>> io_uring_files_cancel include/linux/io_uring.h:35 [inline] >>> exit_files+0xe4/0x170 fs/file.c:456 >>> do_exit+0xae9/0x2930 kernel/exit.c:801 >>> do_group_exit+0x125/0x310 kernel/exit.c:903 >>> get_signal+0x428/0x1f00 kernel/signal.c:2757 >>> arch_do_signal+0x82/0x2470 arch/x86/kernel/signal.c:811 >>> exit_to_user_mode_loop kernel/entry/common.c:161 [inline] >>> exit_to_user_mode_prepare+0x194/0x1f0 kernel/entry/common.c:192 >>> syscall_exit_to_user_mode+0x7a/0x2c0 kernel/entry/common.c:267 >>> entry_SYSCALL_64_after_hwframe+0x44/0xa9 >> >> It seems this fails on "node->shift" in xas_next_entry(), that would >> mean that the node itself was freed while we're iterating on it. >> >> __io_uring_files_cancel() iterates with xas_next_entry() and creates >> XA_STATE once by hand, but it also removes entries in the loop with >> io_uring_del_task_file() -> xas_store(&xas, NULL); without updating >> the iterating XA_STATE. Could it be the problem? See a diff below > > No, the problem is that the lock is dropped after calling > xas_next_entry(), and at any point after calling xas_next_entry(), > the node that it's pointing to can be freed. Only the task itself clears/removes entries, others can only insert. So, could it be freed even though there are no parallel erases? > > I don't think there's any benefit to using the advanced API here. > Since io_uring_cancel_task_requests() can sleep, we have to drop the lock > for each iteration around the loop, and so we have to walk from the top of the tree each time. So we may as well make this easy to read: Thanks for looking into it, looks definitely better. > > @@ -8665,28 +8665,19 @@ static void io_uring_attempt_task_drop(struct file *file, bool exiting) > void __io_uring_files_cancel(struct files_struct *files) > { > struct io_uring_task *tctx = current->io_uring; > - XA_STATE(xas, &tctx->xa, 0); > + struct file *file; > + unsigned long index; > > /* make sure overflow events are dropped */ > tctx->in_idle = true; > > - do { > - struct io_ring_ctx *ctx; > - struct file *file; > - > - xas_lock(&xas); > - file = xas_next_entry(&xas, ULONG_MAX); > - xas_unlock(&xas); > - > - if (!file) > - break; > - > - ctx = file->private_data; > + xa_for_each(&tctx->xa, index, file) { > + struct io_ring_ctx *ctx = file->private_data; > > io_uring_cancel_task_requests(ctx, files); > if (files) > io_uring_del_task_file(file); > - } while (1); > + } > } > > static inline bool io_uring_task_idle(struct io_uring_task *tctx) > > I'll send a proper patch in a few minutes -- I'd like to neaten up a > few of the other XArray uses. > -- Pavel Begunkov