Messages in this thread | | | Subject | Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there | From | Greg Ungerer <> | Date | Fri, 1 May 2020 00:10:05 +1000 |
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On 30/4/20 9:03 am, Linus Torvalds wrote: > On Wed, Apr 29, 2020 at 2:57 PM Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: >> >> I've never had any reason to use FDPIC, and I don't have any binaries >> that would use it. Nicolas Pitre added ARM support, so I guess he >> would be the one to talk to about it. (Added Nicolas.) > > While we're at it, is there anybody who knows binfmt_flat? > > It might be Nicolas too. > > binfmt_flat doesn't do core-dumping, but it has some other oddities. > In particular, I'd like to bring sanity to the installation of the new > creds, and all the _normal_ binfmt cases do it largely close together > with setup_new_exec(). > > binfmt_flat is doing odd things. It's doing this: > > /* Flush all traces of the currently running executable */ > if (id == 0) { > ret = flush_old_exec(bprm); > if (ret) > goto err; > > /* OK, This is the point of no return */ > set_personality(PER_LINUX_32BIT); > setup_new_exec(bprm); > } > > in load_flat_file() - which is also used to loading _libraries_. Where > it makes no sense at all.
I haven't looked at the shared lib support in there for a long time, but I thought that "id" is only 0 for the actual final program. Libraries have a slot or id number associated with them.
> It does the > > install_exec_creds(bprm); > > in load_flat_binary() (which makes more sense: that is only for actual > binary loading, no library case). > > I would _like_ for every binfmt loader to do > > /* Flush all traces of the currently running executable */ > retval = flush_old_exec(bprm); > if (retval) > return retval; > > .. possibly set up personalities here .. > > setup_new_exec(bprm); > install_exec_creds(bprm); > > all together, and at least merge 'setup_new_exec()' with 'install_exec_creds()'. > > And I think all the binfmt handlers would be ok with that, but the > flat one in particular is really oddly set up. > > *Particularly* with that flush_old_exec/setup_new_exec() being done by > the same routine that is also loading libraries (and called from > 'calc_reloc()' from binary loading too). > > Adding Greg Ungerer for m68knommu. Can somebody sort out why that > flush_old_exec/setup_new_exec() isn't in load_flat_binary() like > install_exec_creds() is? > > Most of that file goes back to pre-git days. And most of the commits > since are not so much about binfmt_flat, as they are about cleanups or > changes elsewhere where binfmt_flat was just a victim.
I'll have a look at this.
Quick hack test shows moving setup_new_exec(bprm) to be just before install_exec_creds(bprm) works fine for the static binaries case. Doing the flush_old_exec(bprm) there too crashed out - I'll need to dig into that to see why.
Regards Greg
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