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Re: [Qemu-block] [PATCH v4 1/3] file-posix: Skip effectiveless OFD lock
From: |
Max Reitz |
Subject: |
Re: [Qemu-block] [PATCH v4 1/3] file-posix: Skip effectiveless OFD lock operations |
Date: |
Mon, 1 Oct 2018 21:40:24 +0200 |
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Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 |
On 21.08.18 02:58, Fam Zheng wrote:
> If we know we've already locked the bytes, don't do it again; similarly
> don't unlock a byte if we haven't locked it. This doesn't change the
> behavior, but fixes a corner case explained below.
>
> Libvirt had an error handling bug that an image can get its (ownership,
> file mode, SELinux) permissions changed (RHBZ 1584982) by mistake behind
> QEMU. Specifically, an image in use by Libvirt VM has:
>
> $ ls -lhZ b.img
> -rw-r--r--. qemu qemu system_u:object_r:svirt_image_t:s0:c600,c690 b.img
>
> Trying to attach it a second time won't work because of image locking.
> And after the error, it becomes:
>
> $ ls -lhZ b.img
> -rw-r--r--. root root system_u:object_r:virt_image_t:s0 b.img
>
> Then, we won't be able to do OFD lock operations with the existing fd.
> In other words, the code such as in blk_detach_dev:
>
> blk_set_perm(blk, 0, BLK_PERM_ALL, &error_abort);
>
> can abort() QEMU, out of environmental changes.
>
> This patch is an easy fix to this and the change is regardlessly
> reasonable, so do it.
>
> Signed-off-by: Fam Zheng <address@hidden>
>
> ---
>
> v3: Don't misuse s->perm and s->shared_perm.
> v2: For s == NULL, unlock all bits. [Kevin]
> ---
> block/file-posix.c | 54 +++++++++++++++++++++++++++++++++++++---------
> 1 file changed, 44 insertions(+), 10 deletions(-)
Reviewed-by: Max Reitz <address@hidden>
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