Messages in this thread | | | Date | Thu, 8 Mar 2012 20:05:34 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3 |
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On 03/08, Cyrill Gorcunov wrote: > > On Thu, Mar 08, 2012 at 07:26:23PM +0100, Oleg Nesterov wrote: > > I think that you should do > > > > down_write(&mm->mmap_sem); > > if (mm->num_exe_file_vmas) { > > fput(mm->exe_file); > > mm->exe_file = exe_file; > > exe_file = NULL; > > } > > up_write(&mm->mmap_sem); > > > > to keep the current "mm->exe_file goes away after the final > > unmap(MAP_EXECUTABLE)" logic. > > > > OK, may be this doesn't work in c/r case because you are actually > > going to remove the old mappings? But in this case the new exe_file > > will go away anyway, afaics PR_SET_MM_EXE_FILE is called when you > > still have the old mappings. > > Yes, exactly, I need to remove old mappings first (because VMAs > we're about to restore may intersect with current map the host > program has). And yes, once they all are removed I don't have > /proc/pid/exe anymore. That's why I need num_exe_file_vmas == 0 > case.
OK, in this case PR_SET_MM_EXE_FILE should probably fail if mm->num_exe_file_vmas != 0 ? This way it would be more or less consistent or at least understandable. Just we add the new special case: num_exe_file_vmas == 0 but exe_file != NULL because c/r people are crazy.
> > And I don't think the unconditional > > > > down_write(&mm->mmap_sem); > > set_mm_exe_file(mm, exe_file); > > up_write(&mm->mmap_sem); > > > > is 100% right, this clears ->num_exe_file_vmas. This means that > > (if you still have the old mapping) the new exe_file can go away > > after added_exe_file_vma() + removed_exe_file_vma(). Normally this > > should happen, but afaics this is possible. Note that even, say, > > mprotect() can trigger added_exe_file_vma(). > > > > Wait, Oleg, I'm confused, in case if there *is* exitsting VM_EXECUTABLEs > then we jump into first banch and simply replace old exe_file.
Yes. And then later you remove the old mapping (which do not match the new file anyway) and the new exe_file goes away. Unlikely you want this.
Oleg.
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