Re: IORING_REGISTER_CREDS[_UPDATE]() and credfd_create()?

Jens Axboe
2020-01-30T02:20:57Z

On 1/29/20 6:08 PM, Jens Axboe wrote:
> On 1/29/20 10:34 AM, Jens Axboe wrote:
>> On 1/29/20 7:59 AM, Jann Horn wrote:
>>> On Tue, Jan 28, 2020 at 8:42 PM Jens Axboe <axboe@kernel.dk> wrote:
>>>> On 1/28/20 11:04 AM, Jens Axboe wrote:
>>>>> On 1/28/20 10:19 AM, Jens Axboe wrote:
>>> [...]
>>>>>> #1 adds support for registering the personality of the invoking task,
>>>>>> and #2 adds support for IORING_OP_USE_CREDS. Right now it's limited to
>>>>>> just having one link, it doesn't support a chain of them.
>>> [...]
>>>> I didn't like it becoming a bit too complicated, both in terms of
>>>> implementation and use. And the fact that we'd have to jump through
>>>> hoops to make this work for a full chain.
>>>>
>>>> So I punted and just added sqe->personality and IOSQE_PERSONALITY.
>>>> This makes it way easier to use. Same branch:
>>>>
>>>> https://git.kernel.dk/cgit/linux-block/log/?h=for-5.6/io_uring-vfs-creds
>>>>
>>>> I'd feel much better with this variant for 5.6.
>>>
>>> Some general feedback from an inspectability/debuggability perspective:
>>>
>>> At some point, it might be nice if you could add a .show_fdinfo
>>> handler to the io_uring_fops that makes it possible to get a rough
>>> overview over the state of the uring by reading /proc/$pid/fdinfo/$fd,
>>> just like e.g. eventfd (see eventfd_show_fdinfo()). It might be
>>> helpful for debugging to be able to see information about the fixed
>>> files and buffers that have been registered. Same for the
>>> personalities; that information might also be useful when someone is
>>> trying to figure out what privileges a running process actually has.
>>
>> Agree, that would be a very useful addition. I'll take a look at it.
>
> Jann, how much info are you looking for? Here's a rough start, just
> shows the number of registered files and buffers, and lists the
> personalities registered. We could also dump the buffer info for
> each of them, and ditto for the files. Not sure how much verbosity
> is acceptable in fdinfo?
>
> Here's the test app for personality:
>
> # cat 3
> pos: 0
> flags: 02000002
> mnt_id: 14
> user-files: 0
> user-bufs: 0
> personalities:
> 1: uid=0/gid=0

Here's one that adds the registered buffers and files as well. So
essentially this shows any info on the registered parts.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c5ca84a305d3..e306691bc7a4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6511,6 +6505,55 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
return submitted ? submitted : ret;
}

+static int io_uring_show_cred(int id, void *p, void *data)
+{
+ const struct cred *cred = p;
+ struct seq_file *m = data;
+
+ seq_printf(m, "%5d: uid=%u/gid=%u\n", id, cred->uid.val, cred->gid.val);
+ return 0;
+}
+
+static void __io_uring_show_fdinfo(struct io_ring_ctx *ctx, struct seq_file *m)
+{
+ int i;
+
+ mutex_lock(&ctx->uring_lock);
+ seq_printf(m, "user-files: %d\n", ctx->nr_user_files);
+ for (i = 0; i < ctx->nr_user_files; i++) {
+ struct fixed_file_table *table;
+ struct file *f;
+
+ table = &ctx->file_data->table[i >> IORING_FILE_TABLE_SHIFT];
+ f = table->files[i & IORING_FILE_TABLE_MASK];
+ if (f)
+ seq_printf(m, "%5d: %s\n", i, file_dentry(f)->d_iname);
+ else
+ seq_printf(m, "%5d: <none>\n", i);
+ }
+ seq_printf(m, "user-bufs: %d\n", ctx->nr_user_bufs);
+ for (i = 0; i < ctx->nr_user_bufs; i++) {
+ struct io_mapped_ubuf *buf = &ctx->user_bufs[i];
+
+ seq_printf(m, "%5d: 0x%llx/%lu\n", i, buf->ubuf, buf->len);
+ }
+ if (!idr_is_empty(&ctx->personality_idr)) {
+ seq_printf(m, "personalities:\n");
+ idr_for_each(&ctx->personality_idr, io_uring_show_cred, m);
+ }
+ mutex_unlock(&ctx->uring_lock);
+}
+
+static void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
+{
+ struct io_ring_ctx *ctx = f->private_data;
+
+ if (percpu_ref_tryget(&ctx->refs)) {
+ __io_uring_show_fdinfo(ctx, m);
+ percpu_ref_put(&ctx->refs);
+ }
+}
+
static const struct file_operations io_uring_fops = {
.release = io_uring_release,
.flush = io_uring_flush,
@@ -6521,6 +6564,7 @@ static const struct file_operations io_uring_fops = {
#endif
.poll = io_uring_poll,
.fasync = io_uring_fasync,
+ .show_fdinfo = io_uring_show_fdinfo,
};

static int io_allocate_scq_urings(struct io_ring_ctx *ctx,

--
Jens Axboe