On Wed, Nov 17, 2021 at 10:47:13AM -0800, Kyle Huey wrote: > rr, a userspace record and replay debugger[0], is completely broken on > 5.16rc1. I bisected this to 00b06da29cf9dc633cdba87acd3f57f4df3fd5c7. > > That patch makes two changes, it blocks sigaction from changing signal > handlers once the kernel has decided to force the program to take a > signal and it also stops notifying ptracers of the signal in the same > circumstances. The latter behavior is just wrong. There's no reason > that ptrace should not be able to observe and even change > (non-SIGKILL) forced signals. It should be reverted. > > This behavior change is also observable in gdb. If you take a program > that sets SIGSYS to SIG_IGN and then raises a SIGSYS via > SECCOMP_RET_TRAP and run it under gdb on a good kernel gdb will stop > when the SIGSYS is raised, let you inspect program state, etc. After > the SA_IMMUTABLE change gdb won't stop until the program has already > died of SIGSYS. Ah, hm, this was trying to fix the case where a program trips SECCOMP_RET_KILL (which is a "fatal SIGSYS"), and had been unobservable before. I guess the fix was too broad... -- Kees Cook
