|From:||Eric Paris <eparis-AT-redhat.com>|
|To:||linux-kernel-AT-vger.kernel.org, linux-security-module-AT-vger.kernel.org, selinux-AT-tycho.nsa.gov|
|Subject:||SELinux/SMACK/TOMOYO: ioctl permissions handling is wrong and nonsensicle|
|Date:||Fri, 21 Jan 2011 14:30:35 -0500|
|Cc:||sds-AT-tycho.nsa.gov, jmorris-AT-namei.org, casey-AT-schaufler-ca.com, john.johansen-AT-canonical.com, penguin-kernel-AT-I-love.SAKURA.ne.jp, takedakn-AT-nttdata.co.jp|
[I've included an AA person as well in case you ever decide to try to mediate ioctl operations] SELinux used to recognize certain individual ioctls and check permissions based on the knowledge of the individual ioctl. In commit 242631c49d4cf396 the SELinux code stopped trying to understand individual ioctls and to instead looked at the ioctl access bits to determine in we should check read or write for that operation. This same suggestion was made to SMACK (and I believe copied into TOMOYO). But this suggestion is total rubbish. The ioctl access bits are actually the access requirements for the structure being passed into the ioctl, and are completely unrelated to the operation of the ioctl or the object the ioctl is being performed upon. Take FS_IOC_FIEMAP as an example. FS_IOC_FIEMAP is defined as: FS_IOC_FIEMAP _IOWR('f', 11, struct fiemap) So it has access bits R and W. What this really means is that the kernel is going to both read and write to the struct fiemap. It has nothing at all to do with the operations that this ioctl might perform on the file itself! If anything, our logic is exactly backwards, since an ioctl which writes to userspace would be 'reading' something from the file and an ioctl which reads from userspace would be 'writing' something to the file... I'm planning to revert this SELinux commit, but I want other LSM authors to realize that (assuming I'm not completely off in the woods somewhere) you should take a look at your ioctl permissions checking as well.... -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to email@example.com More majordomo info at http://vger.kernel.org/majordomo-info.html
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