On 17/07/2024 07:33, Jeff Xu wrote:
Consider those cases: I think: a> relying purely on userspace for enforcement does't seem to be effective, e.g. it is trivial to call open(), then mmap() it into executable memory.
If there's a way to do this without running executable code that had to pass a previous execveat() check, then yeah, it's not effective (e.g. a Python interpreter that *doesn't* enforce execveat() is a trivial way to do it).
Once arbitrary code is running, all bets are off. So long as all arbitrary code is being checked itself, it's allowed to do things that would bypass later checks (and it's up to whoever audited it in the first place to prevent this by not giving it the special mark that allows it to pass the check).
b> if both user space and kernel need to call AT_CHECK, the faccessat seems to be a better place for AT_CHECK, e.g. kernel can call do_faccessat(AT_CHECK) and userspace can call faccessat(). This will avoid complicating the execveat() code path. What do you think ? Thanks -Jeff
