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From: Alviro Iskandar Setiawan <[email protected]>
To: Greg Kroah-Hartman <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	Pavel Begunkov <[email protected]>,
	Jens Axboe <[email protected]>,
	Dan Carpenter <[email protected]>,
	kernel test robot <[email protected]>,
	"Chen Rong A." <[email protected]>,
	[email protected],
	io-uring Mailing list <[email protected]>,
	"GNU/Weeb Mailing List" <[email protected]>
Subject: Re: FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree
Date: Sun, 22 Jan 2023 22:43:24 +0700	[thread overview]
Message-ID: <CAOG64qO=iZZO-PJjmeYO5wKHAxn3ATDyj6g=FA_tx3WNAMBvug@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>

On Sun, Jan 22, 2023 at 9:44 PM <[email protected]> wrote:
> The patch below does not apply to the 5.10-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <[email protected]>.

That uninitialized reading is living in 5.10.y branch now
https://github.com/gregkh/linux/blob/v5.10.162/io_uring/io_uring.c#L4989-L5017

If this:

   ret = import_single_range(RE AD, buf, sr->len, &iov, &msg.msg_iter);

fails, this one (flags & MSG_WAITALL) may read an uninitialized
variable because @flags is uninitialized.

Fortunately, if import_single_range() fails, (ret < min_ret) is always
true, so this:

    ret < min_ret || ((flags & MSG_WAITALL)

will always short circuit. But no one tells the compiler if @ret is
always less than @min_ret in that case. So it can't prove that @flags
is never actually read. That still falls to undefined behavior anyway,
the compiler may emit "ud2" or similar trap for that or behave
randomly. IDK...

       reply	other threads:[~2023-01-22 15:43 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
2023-01-22 15:43 ` Alviro Iskandar Setiawan [this message]
2023-01-22 17:47   ` FAILED: patch "[PATCH] io_uring: Clean up a false-positive warning from GCC 9.3.0" failed to apply to 5.10-stable tree Jens Axboe

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