On 01/19, Dmitry V. Levin wrote: > > On Sat, Jan 18, 2025 at 03:13:42PM +0100, Oleg Nesterov wrote: > > On 01/17, Dmitry V. Levin wrote: > [...] > > > For example, on x86_64 sizeof(struct ptrace_syscall_info) is currently 88, > > > while on x86 it is 84. > > > > Not good, but too late to complain... > > Actually, I don't think it's too late to add an extra __u32 padding > there since it wouldn't affect PTRACE_GET_SYSCALL_INFO. Hmm, indeed thanks for correcting me. I forgot that ptrace_get_syscall_info() returns actual_size, not sizeof(). > I can add an explicit padding to the structure if you say > you like it better this way. I dunno, up to you... Well if we add "__u32 padding" at the end, we can probably use sizeof(info) instead of min_size = offsetofend(struct ptrace_syscall_info, seccomp.ret_data) in ptrace_set_syscall_info(), but then it probably makes sense to check info->padding == 0 (just like info.flags || info.reserved) and rename this member to reserved2. Again, up to you, I don't know. > > Currently we have PTRACE_SYSCALL_INFO_SIZE_VER0, when we add the new > > "artificial" member we will have PTRACE_SYSCALL_INFO_SIZE_VER1. Granted, > > this way set_syscall_info() can't use sizeof(info), it should do > > > > ptrace(PTRACE_SET_SYSCALL_INFO, PTRACE_SYSCALL_INFO_SIZE_VER1, info); > > > > and the kernel needs more checks, but this is what I had in mind when I said > > that the 1st version can just require "user_size == PTRACE_SYSCALL_INFO_SIZE_VER0". > > ... it wouldn't be a big deal for user-space to specify also an > appropriate "user_size", e.g. PTRACE_SYSCALL_INFO_SIZE_VER1 when it starts > using the interface available since VER1, but it wouldn't help user-space > programs either as they would have to update "op" and/or "flags" anyway, Sure, and yes, "flags" is needed anyway. > and "user_size" would become just yet another detail they have to care > about. True. It is not that I ever thought that my suggestion could "help user-space". Not at all. Just imo it would be better to fail "early" on the older kernel in the case when user-space expects the "extended" API, even if flags == 0. And no, it is not that I am 100% sure it would be always better. So let me repeat: please do what you think is right, I won't argue. I just tried to understand your points and explain mine to ensure we more or less understand each other. Oleg.
