Messages in this thread | | | Date | Thu, 01 Aug 2013 09:02:23 -0700 | From | Zach Levis <> | Subject | Re: + fs-binfmts-better-handling-of-binfmt-loops.patch added to -mm tree |
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Quoting Oleg Nesterov <oleg@redhat.com>:
> On 07/31, Oleg Nesterov wrote: >> >> > From: Zach Levis <zml@linux.vnet.ibm.com> >> > Subject: fs/binfmts: better handling of binfmt loops >> > >> > With these changes, when a binfmt loop is encountered, the ELOOP will >> > propagate back to the 0 depth. At this point the argv and argc values >> > will be reset to what they were originally and an attempt is made to >> > continue with the following binfmt handlers. >> >> I must admit, I do not really understand why do we want to recover >> after pr_err(). Perhaps the changelog could say a bit more. > > And still can't. Probably I missed something, but it seems that > this tries to "fix" the wrong /proc/sys/fs/binfmt_misc/register... > So an example of what this would be used for (going into commit message of a v2 with your earlier suggestions): A qemu is configured to run 64-bit ELFs on an otherwise 32-bit system. The system's owner switches to running with 64-bit executables, but forgets to disable the binfmt_misc option that redirects 64bit ELFs to qemu. Since the qemu executable is a 64-bit ELF now, binfmt_misc keeps on matching it with the qemu rule, preventing the execution of any 64-bit binary.
With this patch, an error is printed and search_binary_handler() continues on to the next handler, allowing the original executable to run normally so the user can (hopefully) fix their misconfiguration more easily.
>> > + >> > + copy_strings(bprm->argc_orig, *((struct user_arg_ptr *) >> bprm->argv_orig), bprm); >> >> Perhaps it would be more clean to add "struct user_arg_ptr;" >> into binfmts.h and avoid the typecast.
I was kinda trying to avoid exposing the struct, but yeah, that's better. >> >> And I do not think we should ignore the possible error from >> copy_strings(). Even if we know that it succeeded before, another >> thread can, say, unmap this memory in between. > > And since we do copy_strings() again we probably need acct_arg_size() > after remove_arg_zero() loop, although this is not that important. I'm not sure if that's even necessary. It looks like there's copy_strings()->get_arg_page()->acct_arg_size() that's already called. > > And with this patch "depth == 0" check(s) look even worse, imho we > need to cleanup this code first. And proc_exec_connector() looks > simply wrong. I'll try to make a patch. > > But once again, I can be easily wrong, so please correct me. > > Oleg.
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