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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <20230925120309.1731676-9-dhowells@redhat.com>
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Cc:     dhowells@redhat.com, Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Christian Brauner <christian@brauner.io>,
        David Laight <David.Laight@ACULAB.COM>,
        Matthew Wilcox <willy@infradead.org>,
        Jeff Layton <jlayton@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-mm@kvack.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v7 08/12] iov_iter: Don't deal with iter->copy_mc in memcpy_from_iter_mc()
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Date:   Mon, 02 Oct 2023 10:25:51 +0100
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David Howells <dhowells@redhat.com> wrote:

> +static size_t __copy_from_iter_mc(void *addr, size_t bytes, struct iov_=
iter *i)
>  {
> -	struct iov_iter *iter =3D priv2;
> +	size_t progress;
>  =

> -	if (iov_iter_is_copy_mc(iter))
> -		return copy_mc_to_kernel(to + progress, iter_from, len);
> -	return memcpy_from_iter(iter_from, progress, len, to, priv2);
> +	if (unlikely(i->count < bytes))
> +		bytes =3D i->count;
> +	if (unlikely(!bytes))
> +		return 0;
> +	progress =3D iterate_bvec(i, bytes, addr, NULL, memcpy_from_iter_mc);
> +	i->count -=3D progress;

i->count shouldn't be decreased here as iterate_bvec() now does that.

This causes the LTP abort01 test to log a warning under KASAN (see below).
I'll remove the line and repush the patches.

David

    LTP: starting abort01
    =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
    BUG: KASAN: stack-out-of-bounds in __copy_from_iter_mc+0x2e6/0x480
    Read of size 4 at addr ffffc90004777594 by task abort01/708

    CPU: 4 PID: 708 Comm: abort01 Not tainted 99.6.0-rc3-ged6251886a1d #46
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009)/Incus, BIOS unknown=
 2/2/2022
    Call Trace:
     <TASK>
     dump_stack_lvl+0x3d/0x70
     print_report+0xce/0x650
     ? lock_acquire+0x1b1/0x330
     kasan_report+0xda/0x110
     ? __copy_from_iter_mc+0x2e6/0x480
     ? __copy_from_iter_mc+0x2e6/0x480
     __copy_from_iter_mc+0x2e6/0x480
     copy_page_from_iter_atomic+0x517/0x1350
     ? __pfx_copy_page_from_iter_atomic+0x10/0x10
     ? __filemap_get_folio+0x281/0x6c0
     ? folio_wait_writeback+0x53/0x1e0
     ? prepare_pages.constprop.0+0x40b/0x6c0
     btrfs_copy_from_user+0xc6/0x290
     btrfs_buffered_write+0x8c9/0x1190
     ? __pfx_btrfs_buffered_write+0x10/0x10
     ? _raw_spin_unlock+0x2d/0x50
     ? btrfs_file_llseek+0x100/0xf00
     ? follow_page_mask+0x69f/0x1e10
     btrfs_do_write_iter+0x859/0xff0
     ? __pfx_btrfs_file_llseek+0x10/0x10
     ? find_held_lock+0x2d/0x110
     ? __pfx_btrfs_do_write_iter+0x10/0x10
     ? __up_read+0x211/0x790
     ? __pfx___get_user_pages+0x10/0x10
     ? __pfx___up_read+0x10/0x10
     ? __kernel_write_iter+0x3be/0x6d0
     __kernel_write_iter+0x226/0x6d0
     ? __pfx___kernel_write_iter+0x10/0x10
     dump_user_range+0x25d/0x650
     ? __pfx_dump_user_range+0x10/0x10
     ? __pfx_writenote+0x10/0x10
     elf_core_dump+0x231f/0x2e90
     ? __pfx_elf_core_dump+0x10/0x10
     ? do_coredump+0x12a9/0x38c0
     ? kasan_set_track+0x25/0x30
     ? __kasan_kmalloc+0xaa/0xb0
     ? __kmalloc_node+0x6c/0x1b0
     ? do_coredump+0x12a9/0x38c0
     ? get_signal+0x1e7d/0x20f0
     ? 0xffffffffff600000
     ? mas_next_slot+0x328/0x1dd0
     ? lock_acquire+0x162/0x330
     ? do_coredump+0x2537/0x38c0
     do_coredump+0x2537/0x38c0
     ? __pfx_do_coredump+0x10/0x10
     ? kmem_cache_free+0x114/0x520
     ? find_held_lock+0x2d/0x110
     get_signal+0x1e7d/0x20f0
     ? __pfx_get_signal+0x10/0x10
     ? do_send_specific+0xf1/0x1c0
     ? __pfx_do_send_specific+0x10/0x10
     arch_do_signal_or_restart+0x8b/0x4b0
     ? __pfx_arch_do_signal_or_restart+0x10/0x10
     exit_to_user_mode_prepare+0xde/0x210
     syscall_exit_to_user_mode+0x16/0x50
     do_syscall_64+0x53/0x90
     entry_SYSCALL_64_after_hwframe+0x6e/0xd8