On 4/3/19 10:33 AM, Mimi Zohar wrote:
On Wed, 2019-04-03 at 09:10 -0400, Stephen Smalley wrote:
On 4/3/19 7:57 AM, Mimi Zohar wrote:
Let's separate the different types of attacks. From an IMA
perspective, memory attacks are out of scope. That leaves mmap'ed
files, possibly just mmap'ed shared files. Currently IMA can be
configured to verify a file's integrity, based on signatures, being
mmap'ed execute. Assuming that not all files opened require a file
signature, a file could be mmap'ed read/write and later changed to
execute to circumvent the mmap'ed execute signature requirement. If
the existing LSMs are able to prevent this sort of attack, we could
just document this requirement.
I guess I don't understand why IMA isn't already being called from
security_file_mprotect(). security_file_mprotect() could just call
ima_file_mmap(vma->vm_file, prot) if all of the security hooks pass.
SELinux can be used to prevent unauthorized mprotect PROT_EXEC but it
won't perform a measurement of the file if it is allowed by policy.
From a measurement perspective, this will at least measure the file,
but the call to ima_file_mmap() will verify the file signature against
the file, not what is currently in memory, right?
Yes, but you can use SELinux to prevent that (don't allow execmem or
execmod permissions for that domain).
