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1,001 B
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Introduced in commit f37708f6b8 (2.10). The NBD spec says a client
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can request export names up to 4096 bytes in length, even though
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they should not expect success on names longer than 256. However,
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qemu hard-codes the limit of 256, and fails to filter out a client
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that probes for a longer name; the result is a stack smash that can
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potentially give an attacker arbitrary control over the qemu
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process.
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The smash can be easily demonstrated with this client:
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$ qemu-io f raw nbd://localhost:10809/$(printf %3000d 1 | tr ' ' a)
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If the qemu NBD server binary (whether the standalone qemu-nbd, or
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the builtin server of QMP nbd-server-start) was compiled with
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-fstack-protector-strong, the ability to exploit the stack smash
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into arbitrary execution is a lot more difficult (but still
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theoretically possible to a determined attacker, perhaps in
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combination with other CVEs). Still, crashing a running qemu (and
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losing the VM) is bad enough, even if the attacker did not obtain
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full execution control. |