On Mon 2021-11-01 06:04:08, Yafang Shao wrote: > There're many truncated kthreads in the kernel, which may make trouble > for the user, for example, the user can't get detailed device > information from the task comm. > > This patchset tries to improve this problem fundamentally by extending > the task comm size from 16 to 24, which is a very simple way. > > In order to do that, we have to do some cleanups first. > > 1. Make the copy of task comm always safe no matter what the task > comm size is. For example, > > Unsafe Safe > strlcpy strscpy_pad > strncpy strscpy_pad > bpf_probe_read_kernel bpf_probe_read_kernel_str > bpf_core_read_str > bpf_get_current_comm > perf_event__prepare_comm > prctl(2) > > After this step, the comm size change won't make any trouble to the > kernel or the in-tree tools for example perf, BPF programs. > > 2. Cleanup some old hard-coded 16 > Actually we don't need to convert all of them to TASK_COMM_LEN or > TASK_COMM_LEN_16, what we really care about is if the convert can > make the code more reasonable or easier to understand. For > example, some in-tree tools read the comm from sched:sched_switch > tracepoint, as it is derived from the kernel, we'd better make them > consistent with the kernel. The above changes make sense even if we do not extend comm[] array in task_struct. > 3. Extend the task comm size from 16 to 24 > task_struct is growing rather regularly by 8 bytes. This size change > should be acceptable. We used to think about extending the size for > CONFIG_BASE_FULL only, but that would be a burden for maintenance > and introduce code complexity. > > 4. Print a warning if the kthread comm is still truncated. > > 5. What will happen to the out-of-tree tools after this change? > If the tool get task comm through kernel API, for example prctl(2), > bpf_get_current_comm() and etc, then it doesn't matter how large the > user buffer is, because it will always get a string with a nul > terminator. While if it gets the task comm through direct string copy, > the user tool must make sure the copied string has a nul terminator > itself. As TASK_COMM_LEN is not exposed to userspace, there's no > reason that it must require a fixed-size task comm. The amount of code that has to be updated is really high. I am pretty sure that there are more potential buffer overflows left. You did not commented on the concerns in the thread https://lore.kernel.org/all/CAADnVQKm0Ljj-w5PbkAu1ugLFnZRRPt-Vk-J7AhXxDD5xVompA@xxxxxxxxxxxxxx/ Several people suggested to use a more conservative approach. I mean to keep comm[16] as is and add a new pointer to the full name. The buffer for the long name might be dynamically allocated only when needed. The pointer might be either in task_struct or struct kthread. It might be used the same way as the full name stored by workqueue kthreads. The advantage of the separate pointer: + would work for names longer than 32 + will not open security holes in code Best Regards, Petr
