Messages in this thread | | | Date | Thu, 3 Sep 2020 02:17:19 -0400 | From | Rich Felker <> | Subject | Re: [PATCH 3/4] sh: Add SECCOMP_FILTER |
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On Thu, Sep 03, 2020 at 08:04:44AM +0200, John Paul Adrian Glaubitz wrote: > On 9/3/20 7:46 AM, Rich Felker wrote: > > > > OK, I think I have an explanation for the mechanism of the bug, and it > > really is a combination of the 2008 bug (confusion of r0 vs r3) and > > the SECCOMP_FILTER commit. When the syscall_trace_entry code path is > > in use, a syscall with argument 5 having value -1 causes > > do_syscall_trace_enter to return -1 (because it returns regs[0], which > > contains argument 5), which the change in entry-common.S interprets as > > a sign to skip the syscall and jump to syscall_exit, and things blow > > up from there. In particular, SYS_mmap2 is almost always called with > > -1 as the 5th argument (fd), and this is even more common on nommu > > where SYS_brk does not work. > > > > I'll follow up with a new proposed patch. > > I'm not sure whether we need another revision of your first patch. Your > previous analysis was at least right regarding the tests 51 and 58 > but those have been fixed now. > > But there were two other tests failing, weren't there? > > I have to recheck later, I just got up (it's 8 AM CEST).
The first patch was surely not right; setting syscall_nr to -1 and letting it -ENOSYS clobbered any return value set by the seccomp filters. The one I've sent now should be right. I'll follow up after testing with libseccomp test cases.
Rich
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