From: Andrew Morton <akpm@linux-foundation.org>
To: "Shengzhuo Wei" <me@cherr.cc>
Cc: "John Stultz" <johnstul@us.ibm.com>, "Yao Zi" <me@ziyao.cc>,
<linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
Alexey Dobriyan <adobriyan@gmail.com>
Subject: Re: [PATCH] proc: fix comm_write return value when truncated or error
Date: Fri, 24 Apr 2026 03:50:28 -0700 [thread overview]
Message-ID: <20260424035028.a811dd6bc8248b640a9fd7c2@linux-foundation.org> (raw)
In-Reply-To: <20260424-fix_proc_write_return-v1-1-7a793c2aad32@cherr.cc>
On Fri, 24 Apr 2026 04:06:21 +0800 "Shengzhuo Wei" <me@cherr.cc> wrote:
> When count exceeds TASK_COMM_LEN-1, comm_write() copies at most
> TASK_COMM_LEN-1 bytes but returns the original count. This violates
> write(2) semantics, which require returning the number of bytes
> actually written.
>
> The count parameter is size_t and should not be repurposed to carry a
> negative error code on the same_thread_group() failure path.
>
> Introduce a local len for the truncated length and a separate ssize_t
> ret for the return value.
Looks right to me.
> Fixes: 4614a696bd1c ("procfs: allow threads to rename siblings via /proc/pid/tasks/tid/comm")
December 2009.
Hopefully no userspace is depending on the broken return value of a
write to /proc/pid/comm.
Arguably we should leave the code as-is and add an apologetic comment
explaining the situation.
next prev parent reply other threads:[~2026-04-24 10:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-23 20:06 [PATCH] proc: fix comm_write return value when truncated or error Shengzhuo Wei
2026-04-24 10:50 ` Andrew Morton [this message]
2026-04-24 13:28 ` Alexey Dobriyan
2026-04-24 18:03 ` Shengzhuo Wei
2026-04-24 18:52 ` Alexey Dobriyan
2026-04-24 13:35 ` Andrew Morton
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