Messages in this thread | | | Date | Wed, 31 Jul 2013 22:08:05 +0200 | From | Oleg Nesterov <> | Subject | Re: + fs-binfmts-better-handling-of-binfmt-loops.patch added to -mm tree |
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> 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.
> --- a/fs/exec.c~fs-binfmts-better-handling-of-binfmt-loops > +++ a/fs/exec.c > @@ -1403,13 +1403,40 @@ int search_binary_handler(struct linux_b > if (!try_module_get(fmt->module)) > continue; > read_unlock(&binfmt_lock); > + bprm->previous_binfmts[1] = bprm->previous_binfmts[0]; > + bprm->previous_binfmts[0] = fmt; > + > bprm->recursion_depth = depth + 1; > retval = fn(bprm); > bprm->recursion_depth = depth; > + if (retval == -ELOOP && depth == 0) { /* cur, previous */ > + pr_err("Too much recursion with binfmts (0:%s, -1:%s) in file %s, skipping (base %s).\n", > + bprm->previous_binfmts[0]->name, > + bprm->previous_binfmts[1]->name, > + bprm->filename, > + fmt->name); > + > + /* Put argv back in its place */ > + while (bprm->argc > 0) { > + retval = remove_arg_zero(bprm); > + if (retval) > + return retval; > + }
But why do we need this?
Afaics we only need to restore bprm->p to the old value before the 1st do_execve_common()->copy_strings(argv) and nothing else, no ? free_bprm()->free_arg_pages() will do the necessary cleanup in any case.
> + > + 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.
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.
> + bprm->argc = bprm->argc_orig;
Or we can simply do count() again. compared to copy_strings() this is cheap.
Oleg.
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