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Creating an image that requires format probing of the backing image is potentially unsafe (we've had several CVEs over the years based on probes leaking information to the guest on a subsequent boot, although these days tools like libvirt are aware of the issue enough to prevent the worst effects). For example, if our probing algorithm ever changes, or if other tools like libvirt determine a different probe result than we do, then subsequent use of that backing file under a different format will present corrupted data to the guest. Fortunately, the worst effects occur only when the backing image is originally raw, and we at least prevent commit into a probed raw backing file that would change its probed type. Still, it is worth starting a deprecation clock so that future qemu-img can refuse to create backing chains that would rely on probing, to encourage clients to avoid unsafe practices. Most warnings are intentionally emitted from bdrv_img_create() in the block layer, but qemu-img convert uses bdrv_create() which cannot emit its own warning without causing spurious warnings on other code paths. In the end, all command-line image creation or backing file rewriting now performs a check. Furthermore, if we probe a backing file as non-raw, then it is safe to explicitly record that result (rather than relying on future probes); only where we probe a raw image do we care about further warnings to the user when using such an image (for example, commits into a probed-raw backing file are prevented), to help them improve their tooling. But whether or not we make the probe results explicit, we still warn the user to remind them to upgrade their workflow to supply -F always. iotest 114 specifically wants to create an unsafe image for later amendment rather than defaulting to our new default of recording a probed format, so it needs an update. While touching it, expand it to cover all of the various warnings enabled by this patch. iotest 301 also shows a change to qcow messages. Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <20200706203954.341758-11-eblake@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
24 lines
1.4 KiB
Plaintext
24 lines
1.4 KiB
Plaintext
QA output created by 114
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qemu-img: warning: Deprecated use of backing file without explicit backing format (detected format of raw)
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.orig
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Formatting 'TEST_DIR/t.IMGFMT.base', fmt=IMGFMT size=67108864
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qemu-img: warning: Deprecated use of backing file without explicit backing format
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qemu-img: warning: Deprecated use of backing file without explicit backing format (detected format of IMGFMT)
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base backing_fmt=IMGFMT
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qemu-img: warning: Deprecated use of unopened backing file without explicit backing format, use of this image requires potentially unsafe format probing
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Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=67108864 backing_file=TEST_DIR/t.IMGFMT.base
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image: TEST_DIR/t.IMGFMT
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file format: IMGFMT
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virtual size: 64 MiB (67108864 bytes)
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cluster_size: 65536
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backing file: TEST_DIR/t.IMGFMT.base
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backing file format: foo
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qemu-io: can't open device TEST_DIR/t.qcow2: Could not open backing file: Unknown driver 'foo'
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no file open, try 'help open'
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read 4096/4096 bytes at offset 0
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4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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qemu-img: warning: Deprecated use of backing file without explicit backing format, use of this image requires potentially unsafe format probing
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read 4096/4096 bytes at offset 0
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4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
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*** done
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