Re: [PATCH v4 2/3] treewide: Switch memcpy() users of 'task->comm' to a more safer implementation

Yafang Shao
2025-05-22T06:15:51Z

On Wed, May 21, 2025 at 2:24 PM Bhupesh <bhupesh@igalia.com> wrote:
>
> As Linus mentioned in [1], currently we have several memcpy() use-cases
> which use 'current->comm' to copy the task name over to local copies.
> For an example:
>
> ...
> char comm[TASK_COMM_LEN];
> memcpy(comm, current->comm, TASK_COMM_LEN);
> ...
>
> These should be modified so that we can later implement approaches
> to handle the task->comm's 16-byte length limitation (TASK_COMM_LEN)
> is a more modular way (follow-up patches do the same):
>
> ...
> char comm[TASK_COMM_LEN];
> memcpy(comm, current->comm, TASK_COMM_LEN);
> comm[TASK_COMM_LEN - 1] = '\0';
> ...
>
> The relevant 'memcpy()' users were identified using the following search
> pattern:
> $ git grep 'memcpy.*->comm\>'

Hello Bhupesh,

Several BPF programs currently read task->comm directly, as seen in:

// tools/testing/selftests/bpf/progs/test_skb_helpers.c [0]
bpf_probe_read_kernel_str(&comm, sizeof(comm), &task->comm);

This approach may cause issues after the follow-up patch.
I believe we should replace it with the safer bpf_get_current_comm()
or explicitly null-terminate it with "comm[sizeof(comm) - 1] = '\0'".
Out-of-tree BPF programs like BCC[1] or bpftrace[2] relying on direct
task->comm access may also break and require updates.

[0]. https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/progs/test_skb_helpers.c#n26
[1]. https://github.com/iovisor/bcc
[2]. https://github.com/bpftrace/bpftrace

--
Regards
Yafang