On Tue, Aug 02, 2022 at 09:40:50PM +0200, Helge Deller wrote: > On 8/1/22 18:57, Josh Triplett wrote: > > On Mon, Aug 01, 2022 at 05:20:13PM +0200, Helge Deller wrote: > >> This patch series allows the arch-specific kernel fault handlers to dump > >> in addition to the typical info (IP address, fault type, backtrace and so on) > >> the command line of the faulting process. > >> > >> The motivation for this patch is that it's sometimes quite hard to find out and > >> annoying to not know which program *exactly* faulted when looking at the syslog. > >> > >> Some examples from the syslog are: > >> > >> On parisc: > >> do_page_fault() command='cc1' type=15 address=0x00000000 in libc-2.33.so[f6abb000+184000] > >> CPU: 1 PID: 13472 Comm: cc1 Tainted: G E 5.10.133+ #45 > >> Hardware name: 9000/785/C8000 > >> > >> -> We see the "cc1" compiler crashed, but it would be useful to know which file was compiled. > >> > >> With this patch series, the kernel now prints in addition: > >> cc1[13472] cmdline: /usr/lib/gcc/hppa-linux-gnu/12/cc1 -quiet @/tmp/ccRkFSfY -imultilib . -imultiarch hppa-linux-gnu -D USE_MINIINTERPRETER -D NO_REGS -D _HPUX_SOURCE -D NOSMP -D THREADED_RTS -include /build/ghc/ghc-9.0.2/includes/dist-install/build/ghcversion.h -iquote compiler/GHC/Iface -quiet -dumpdir /tmp/ghc13413_0/ -dumpbase ghc_5.hc -dumpbase-ext .hc -O -Wimplicit -fno-PIC -fwrapv -fno-builtin -fno-strict-aliasing -o /tmp/ghc13413_0/ghc_5.s > >> > >> -> now we know that cc1 crashed while compiling some haskell code. > > > > This does seem really useful for debugging. > > Yes. > > > However, it's also an information disclosure in various ways. The > > arguments of a program are often more sensitive than the name, and logs > > have a tendency to end up in various places, such as bug reports. > > > > An example of how this can be an issue: > > - You receive an email or other message with a sensitive link to follow > > - You open the link, which launches `firefox https://...` > > - You continue browsing from that window > > - Firefox crashes (and recovers and restarts, so you don't think > > anything of it) > > - Later, you report a bug on a different piece of software, and the bug > > reporting process includes a copy of the kernel log > > Yes, that's a possible way how such information can leak. > > > I am *not* saying that we shouldn't do this; it seems quite helpful. > > However, I think we need to arrange to treat this as sensitive > > information, similar to kptr_restrict. > > I wonder what the best solution could be. > > A somewhat trivial solution is to combine it with the dmesg_restrict sysctl, e.g.: > > * When ``dmesg_restrict`` is set to 0 there are no restrictions for users to read > dmesg. In this case my patch would limit the information (based on example above): > cc1[13472] cmdline: /usr/lib/gcc/hppa-linux-gnu/12/cc1 [note: other parameters hidden due to dmesg_restrict=0 sysctl] > So it would show the full argv[0] with a hint that people would need to change dmesg_restrict. > > * When ``dmesg_restrict`` is set to 1, users must have ``CAP_SYSLOG`` to use dmesg(8) > and the patch could output all parameters: > cc1[13472] cmdline: /usr/lib/gcc/hppa-linux-gnu/12/cc1 -quiet @/tmp/ccRkFSfY -imultilib . -imultiarch hppa-linux-gnu .... > > That would of course still leave few possible corner-cases where information > could leak, but since usually programs shouldn't crash and that > people usually shouldn't put sensitive information into the parameter > list directly, it's somewhat unlikely to happen. > > Another different solution would be to add another sysctl. > > Any other ideas? I don't think we should overload the meaning of dmesg_restrict. But overloading kptr_restrict seems reasonable to me. (Including respecting kptr_restrict==2 by not showing this at all.)
