On Wed, Jan 26, 2022 at 10:57:29AM -0600, Eric W. Biederman wrote: > Matthew Wilcox <willy@xxxxxxxxxxxxx> writes: > > > On Wed, Jan 26, 2022 at 11:44:47AM +0000, Ariadne Conill wrote: > >> Interestingly, Michael Kerrisk opened an issue about this in 2008[1], > >> but there was no consensus to support fixing this issue then. > >> Hopefully now that CVE-2021-4034 shows practical exploitative use > >> of this bug in a shellcode, we can reconsider. > >> > >> [0]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html > >> [1]: https://bugzilla.kernel.org/show_bug.cgi?id=8408 > > > > Having now read 8408 ... if ABI change is a concern (and I really doubt > > it is), we could treat calling execve() with a NULL argv as if the > > caller had passed an array of length 1 with the first element set to > > NULL. Just like we reopen fds 0,1,2 for suid execs if they were > > closed. > > Where do we reopen fds 0,1,2 for suid execs? I feel silly but I looked > through the code fs/exec.c quickly and I could not see it. I'm wondering if I misremembered and it's being done in ld.so rather than in the kernel? That might be the right place to put this fix too. > I am attracted to the notion of converting an empty argv array passed > to the kernel into something we can safely pass to userspace. > > I think it would need to be having the first entry point to "" instead > of the first entry being NULL. That would maintain the invariant that you > can always dereference a pointer in the argv array. Yes, I like that better than NULL.
