On Sun, 2024-02-25 at 14:51 +0800, Icenowy Zheng wrote: > > From my point of view, I prefer to "restore fstat", because we need > > to > > use the Chrome sandbox everyday (even though it hasn't been upstream > > by now). But I also hope "seccomp deep argument inspection" can be > > solved in the future. > > My idea is this problem needs syscalls to be designed with deep > argument inspection in mind; syscalls before this should be considered > as historical error and get fixed by resotring old syscalls. I'd not consider fstat an error as using statx for fstat has a performance impact (severe for some workflows), and Linus has concluded "if the user wants fstat, give them fstat" for the performance issue: https://sourceware.org/pipermail/libc-alpha/2023-September/151365.html However we only want fstat (actually "newfstat" in fs/stat.c), and it seems we don't want to resurrect newstat, newlstat, newfstatat, etc. (or am I missing any benefit - performance or "just pleasing seccomp" - of them comparing to statx?) so we don't want to just define __ARCH_WANT_NEW_STAT. So it seems we need to add some new #if to fs/stat.c and include/uapi/asm-generic/unistd.h. And no, it's not a design issue of all other syscalls. It's just the design issue of seccomp. There's no way to design a syscall allowing seccomp to inspect a 100-character path in its argument unless refactoring seccomp entirely because we cannot fit a 100-character path into 8 registers. As at now people do use PTRACE_PEEKDATA for "deep inspection" (actually "debugging" the target process) but it obviously makes a very severe performance impact. <rant> Today the entire software industry is saying "do things in a declarative way" but seccomp is completely the opposite. It's auditing *how* the sandboxed application is doing things instead of *what* will be done. I've raised my against to seccomp and/or syscall allowlisting several times after seeing so many breakages like: - https://github.com/NetworkConfiguration/dhcpcd/issues/120 - https://gitlab.gnome.org/GNOME/tracker-miners/-/issues/252 - https://blog.pintia.cn/2018/06/27/glibc-segmentation-fault/ - http://web.archive.org/web/20210126121421/http://acm.xidian.edu.cn/discuss/thread.php?tid=148&cid=# (comment 3) but people just keep telling me "you are wrong, you don't understand security". Some of them even complain "seccomp is broken" as well but still keep using it. </rant> -- Xi Ruoyao <xry111@xxxxxxxxxxx> School of Aerospace Science and Technology, Xidian University
