Dominique Martinet wrote on Thu, Jan 24, 2019: > I was thinking of something along the lines of: > return vma_is_anonymous(vma) || (vma->vm_file && > (inode_owner_or_capable(file_inode(vma->vm_file)) > || inode_permission(file_inode(vma->vm_file), > MAY_WRITE) == 0)); > > I dropped the first f_mode check because none of the known mincore users > open the files read-write, and the check is redundant with > inode_permission() so while it would probably be an optimisation in some > cases I do not think it is useful in practice. > On the other hand, I have no idea how expensive the inode_permission and > owner checks really are - do they try to refresh attributes on a > networked filesystem or would it trust the cache or is it fs dependant? > > Honestly this is more a case of "the people who's be interested in > seeing this have no idea what they're doing" than lack of interest.. I > wouldn't mind if there were tests doing mincore on a bunch of special > files/mappings but I just tried on a few regular files by hand, this > isn't proper coverage; I'll try to take more time to test various > mappings today (JST).
I've done some tests with this, it appears OK. Obviously the tests I previously had done still work: - user's own files are ok, even if read-only now. - non-user writable files are ok. - non-user non-writable files (e.g. system libs) aren't. - root can still do anything. On new tests: - there are vmas with no file that aren't anonymous and come all the way there (vvar and vdso), so factoring vma->vm_file check is definitely needed. - vsyscall doesn't reach can_do_mincore() - [heap] [stack] and other fileless regular maps are anonymous - I tried a char device (/dev/zero) and it was marked anonymous despite mapping with MAP_SHARED, which is somewhat expected I guess? - I couldn't map /proc or /sys files (no such device), so no mincore there. I'd post my test program but I actually added pr_info messages in can_do_mincore to check what it returned because madvise dontneed isn't guaranteed to evict pages so we can't rely on madvise dontneed + mincore to return 0; not sure what to do for ltp... If anyone has a good idea of how to check if mincore actually got granted permissions without drop_caches I'll post to the ltp github. Anything else to try? Jiri, you've offered resubmitting the last two patches properly, can you incorporate this change or should I just send this directly? (I'd take most of your commit message and add your name somewhere) Thanks, -- Dominique
