Messages in this thread | | | Date | Mon, 5 Mar 2012 13:14:36 -0800 | From | Matt Helsley <> | Subject | Re: [PATCH 0/1] turn mm->exe_file into mm->exe_path |
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On Mon, Mar 05, 2012 at 04:28:26PM +0100, Oleg Nesterov wrote: > I think the patch is simple and self-explanatory, it simply > does s/mm->exe_file/mm->exe_path/. > > Why do we need mm->exe_file? IIUC, there are 2 reasons: > > 1. we do not want O(n) proc/pid/exe looking for the 1st > VM_EXECUTABLE vma.
(Frankly this always seemed like a bit of a hack to me. If someone got creative with text layout then it could break this hack...)
> > 2. we do not want to rely on vma->vm_file->f_path, > bprm->file->f_op->mmap can change ->vm_file. > > Unless there was another subtle reason, "struct path *exe_path" > can equally work but it looks more clear.
PATCH 1/1 looks fine. I think Alexey Dobriyan was working on a similar patch years ago.
> And can't we also remove added_exe_file_vma/removed_exe_file_vma? > Why do we need mm->num_exe_file_vmas? Afaics it is only needed to > "free" mm->exe_file if the application unmaps all these vmas. Say, > to allow to unmount fs.
Yup. I know it's not pretty to have to track the exe file refs this way but I couldn't see any other way to keep a reference to the file (or path) and avoid pinning the mounted filesystem the exectuable is on.
> Can't we simply add PR_CLEAR_MM_EXE_PATH instead? Of course it is > not enough if ->vm_file still has a reference. But c/r people want
Relying solely on this prctl would break existing programs. I believe Al Viro's example was a program that copies its text to a new executable area, unmaps the original, performs a pivot_root(), and finally umounts the old root. Removing the counter would cause the mount to be pinned for these programs and the umount would fail.
> PR_SET_MM_EXE_FILE anyway, see http://marc.info/?t=133052865500016 > So perhaps we can add PR_SET_MM_EXE_PATH which accepts NULL as well > and kill this counter? > > Oleg.
Cheers, -Matt Helsley
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