Hey Zach, On 10/21/22 18:16, Zach O'Keefe wrote:
Hey Alex! Thanks for taking the time to review! On Fri, Oct 21, 2022 at 5:41 AM Alejandro Colomar <alx.manpages@xxxxxxxxx> wrote:On 10/21/22 14:37, Alejandro Colomar wrote:On 10/19/22 01:50, Zach OKeefe wrote:From: Zach O'Keefe <zokeefe@xxxxxxxxxx> The initial commit of process_madvise(2) to man-pages project included an error, indicating that CAP_SYS_ADMIN capability was required when, in fact, CAP_SYS_NICE was the required capability. The initial commit of process_madvise(2) to Linux, commit ecb8ac8b1f14 ("mm/madvise: introduce process_madvise() syscall: an external memory hinting API"), relied on PTRACE_MODE_ATTACH_FSCREDS (see ptrace(2)), but was amended by commit 96cfe2c0fd23 ("mm/madvise: replace ptrace attach requirement for process_madvise") which replaced this with a combination of PTRACE_MODE_READ and CAP_SYS_NICE (PTRACE_MODE_READ to prevent leaking ASLR metadata and CAP_SYS_NICE for influencing process performance).[...]If I understand the paragraph above, from 5.10 to 5.12 the capability required was CAP_SYS_ADMIN?Or was it CAP_SYS_PTRACE?Starting in 5.10, there was no CAP_* capability requirement - only PTRACE_MODE_ATTACH_FSCREDS (aka PTRACE_MODE_ATTACH | PTRACE_MODE_REALCREDS). Now, my understanding of the algorithm employed for ptrace access mode checking isn't to be trusted, but AFAIK, a caller having CAP_SYS_PTRACE in the target's user namespace (directly or transitively) isn't required to pass this (though it makes it easier). ptrace(2) has an overview of the algorithm. Starting in 5.12, CAP_SYS_NICE was added as a requirement, and the ptrace algorithm used changed to PTRACE_MODE_READ.
Understood.
If you think recording the differences in kernel versions in the man-page is important, let me know and I can amend this patch.
Yes; since it was live during 2 versions, I think we should at least mention it. A couple of lines in NOTES might be enough.
Thanks, Alex
Thanks, Zcah-- <http://www.alejandro-colomar.es/>
-- <http://www.alejandro-colomar.es/>
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