On 7/13/19 12:17 AM, Jakub Jankowski wrote: > On 2019-07-12, Alexey Izbyshev wrote: > >> On 7/12/19 8:46 PM, Alexey Dobriyan wrote: >>> The proper fix to all /proc/*/cmdline problems is to revert >>> >>> f5b65348fd77839b50e79bc0a5e536832ea52d8d >>> proc: fix missing final NUL in get_mm_cmdline() rewrite >>> >>> 5ab8271899658042fabc5ae7e6a99066a210bc0e >>> fs/proc: simplify and clarify get_mm_cmdline() function >>> >> Should this be interpreted as an actual suggestion to revert the patches, >> fix the conflicts, test and submit them, or is this more like thinking out >> loud? In the former case, will it be OK for long term branches? >> >> get_mm_cmdline() does seem easier to read for me before 5ab8271899658042. >> But it also has different semantics in corner cases, for example: >> >> - If there is no NUL at arg_end-1, it reads only the first string in >> the combined arg/env block, and doesn't terminate it with NUL. >> >> - If there is any problem with access_remote_vm() or copy_to_user(), >> it returns -EFAULT even if some data were copied to userspace. >> >> On the other hand, 5ab8271899658042 was merged not too long ago (about a year), >> so it's possible that the current semantics isn't heavily relied upon. > > I posted this (corner?) case ~3 months ago, unfortunately it wasn't picked up by anyone: https://lkml.org/lkml/2019/4/5/825 > You can treat it as another datapoint in this discussion. > Thanks, this is interesting. Perl explicitly relies on special treatment of non-NUL at arg_end-1 in pre-5ab8271899658042: on argv0 replace, it fills everything after the new argv0 in the combined argv/env block with spaces [1,2]. While personally I don't approve what Perl does here, 5ab8271899658042 did change the user-visible behavior in this case. [1] https://perl5.git.perl.org/perl.git/blob/86b50d930caa:/mg.c#l2733 [2] https://perl5.git.perl.org/perl.git/blob/86b50d930caa:/perl.c#l1698 Alexey > > Regards, > Jakub >
