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io_uring: don't assume mm is constant across submits 

If we COW the identity, we assume that ->mm never changes. But this
isn't true of multiple processes end up sharing the ring. Hence treat
id->mm like like any other process compontent when it comes to the
identity mapping. This is pretty trivial, just moving the existing grab
into io_grab_identity(), and including a check for the match.

Cc: stable@vger.kernel.org # 5.10
Fixes: 1e6fa5216a ("io_uring: COW io_identity on mismatch")
Reported-by: Christian Brauner <christian.brauner@ubuntu.com>:
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>:
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2020-12-29 10:50:46 -07:00
parent 5c8fe583cc
commit 77788775c7
1 changed files with 7 additions and 7 deletions
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14
fs/io_uring.c
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@ -1501,6 +1501,13 @@ static bool io_grab_identity(struct io_kiocb *req)
spin_unlock_irq(&ctx->inflight_lock);
req->work.flags |= IO_WQ_WORK_FILES;
}
if (!(req->work.flags & IO_WQ_WORK_MM) &&
(def->work_flags & IO_WQ_WORK_MM)) {
if (id->mm != current->mm)
return false;
mmgrab(id->mm);
req->work.flags |= IO_WQ_WORK_MM;
}
return true;
}
@ -1525,13 +1532,6 @@ static void io_prep_async_work(struct io_kiocb *req)
req->work.flags |= IO_WQ_WORK_UNBOUND;
}
/* ->mm can never change on us */
if (!(req->work.flags & IO_WQ_WORK_MM) &&
(def->work_flags & IO_WQ_WORK_MM)) {
mmgrab(id->mm);
req->work.flags |= IO_WQ_WORK_MM;
}
/* if we fail grabbing identity, we must COW, regrab, and retry */
if (io_grab_identity(req))
return;