ide_dma_cb: Assertion `prep_size >= 0 && prep_size <= n * 512' failed.
Bug #1883739 reported by
Bugs SysSec
This bug affects 1 person
| Affects | Status | Importance | Assigned to | Milestone | |
|---|---|---|---|---|---|
| QEMU |
Confirmed
|
Undecided
|
John Snow | ||
Bug Description
To reproduce run the QEMU with the following command line:
```
qemu-system-x86_64 -cdrom hypertrash.iso -nographic -m 100 -enable-kvm -net none -drive id=disk,
```
QEMU Version:
```
# qemu-5.0.0
$ ./configure --target-
$ x86_64-
QEMU emulator version 5.0.0
Copyright (c) 2003-2020 Fabrice Bellard and the QEMU Project developers
```
To create disk image run:
```
dd if=/dev/zero of=hda.img bs=1024 count=1024
```
Revision history for this message
| Bugs SysSec (bugs-syssec) wrote | #1 |
Revision history for this message
| John Snow (jnsnow) wrote | #2 |
| Changed in qemu: | |
| status: | New → Confirmed |
| Changed in qemu: | |
| assignee: | nobody → John Snow (jnsnow) |
To post a comment you must log in.
ACK. I do not have time to fix this bug at the moment under the belief that it's likely low-priority and only "misbehaving guests" can trigger it. Some advice:
1. Do not use IDE in production deployments after initial installation, if you can help it. Use a performant virtio solution.
2. If anyone would like to fix this problem, I will be more than happy to point you to the exact lines of code that cause the problem. I think the fix will be easy, but testing will be time-consuming as it involves understanding error behavior of real hardware that I don't personally have the setup to quickly test or verify.
From memory: the problem is that ide_dma_cb expects that it was able to prepare at least one sector's worth of scatter-gather list to begin DMA, but it's possible to give malformed SG lists where IDE is unable to process the remainder of a sector in a list.
It was not clear to me at the time when I first investigated this what a real controller would do if it got an incomplete sector and how it should signal that.
It was also not clear to me if the sg_prepare function for the pci bmdma controller would ever encounter a situation where further entries in the list might be received "later" and we should "wait" for them.
If this bug is more dangerous than a self-inflicted DOS, please let me know and I'll re-prioritize. Patches, email and IRC chats welcome.
--js