Messages in this thread | | | Date | Wed, 04 Apr 2018 22:49:30 +0200 | From | Oleksandr Natalenko <> | Subject | Re: usercopy whitelist woe in scsi_sense_cache |
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Hi.
On středa 4. dubna 2018 22:21:53 CEST Kees Cook wrote: > ... > That means scsi_sense_cache should be 96 bytes in size? But a 22 byte > read starting at offset 94 happened? That seems like a 20 byte read > beyond the end of the SLUB object? Though if it were reading past the > actual end of the object, I'd expect the hardened usercopy BUG (rather > than the WARN) to kick in. Ah, it looks like > /sys/kernel/slab/scsi_sense_cache/slab_size shows this to be 128 bytes > of actual allocation, so the 20 bytes doesn't strictly overlap another > object (hence no BUG): > ...
Actually, I can trigger a BUG too:
[ 129.259213] usercopy: Kernel memory exposure attempt detected from SLUB object 'scsi_sense_cache' (offset 119, size 22)! [ 129.265167] ------------[ cut here ]------------ [ 129.267579] kernel BUG at mm/usercopy.c:100!
And also offset can be different, as you may see:
[ 55.993224] Bad or missing usercopy whitelist? Kernel memory exposure attempt detected from SLUB object 'scsi_sense_cache' (offset 76, size 22)! [ 55.998678] WARNING: CPU: 0 PID: 1305 at mm/usercopy.c:81 usercopy_warn +0x7e/0xa0
It looks like only the size stays the same.
> Can you send me your .config? What SCSI drivers are you using in the > VM and on the real server?
This is an Arch kernel with a config available here [1].
For both server and VM "lspci -vv" shows "ahci" in use. Is this what you are asking for?
> Are you able to see what ioctl()s smartctl is issuing? I'll try to > reproduce this on my end...
As per [2], strace shows "SG_IO" requests. Is this detailed enough?
Thanks for looking into it.
Regards, Oleksandr
[1] https://git.archlinux.org/svntogit/packages.git/plain/trunk/config? h=packages/linux&id=d7625be23f83416491d202d5cea96e5a871fb216 [2] https://gist.github.com/6f58f8891468aeba1ab2cc9f45668735
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