From nobody Thu Dec 18 12:51:55 2025 Received: from fanzine2.igalia.com (fanzine2.igalia.com [213.97.179.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BA528236440; Wed, 7 May 2025 11:05:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.97.179.56 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746615922; cv=none; b=i9k7/WhFFjZb4Ha09VUSB4m4UFw1qcGRY7B2yq7BIbtUT1JIg720qbJcTwVATZrj1v2LIzMPP9A2SRKFiDLFKUrXAM0FlVcXvykcUZh5s0xDGPpK7wf4riqxhYfRGeVmP66KiRn/Uxzk/UDymD/+Wpg1j7xFCoJNQsyYXzDsM6Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746615922; c=relaxed/simple; bh=7XqKkySLH3XnP5dCcWNxk+0DtN1bkrte9oK/saSgtts=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=NkicUFrTvhY138a/CCgpQMK24xtIgJeOUid3Fx8kFtDRyFdUQhmKy1l/n68I2grxddwLbcEtfFaL8dpG+++W/kFk+6FSHRhJRDXkRK762JniHJhmJoQiXleq8YkgQQ2hMxSNv5kLT6E002eqiqZJcg23owUX7EX/+bul+9kjeVg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com; spf=pass smtp.mailfrom=igalia.com; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b=c+V9v308; arc=none smtp.client-ip=213.97.179.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=igalia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="c+V9v308" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Sender:Reply-To:Content-Type:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=51AuBhOBwcqdxbUaoVuoZuKLaFvWUDOFVfRKxcUsvBc=; b=c+V9v308TdkSpaG+OfUH7HAacT 9/B9haik3YVxK0Ia3scGUjrCntDrNaLtCbHYvRr2HNnjF7DVkLEicy0+dtcxdd2NlxYVC1gLPGtt7 n8ibJh4vHTvLTsjgyF5oXT788+GUY0ltDBPXOAhKweJeJZr5ZYypXBOVik9/+ipxGfij5ozXQoDTK hMwpeT2LSMeUG3TWyYhsjTij331Vx2F16L9PFbz6qLBFUu3Dxk8ClrOAuwC/4x18wvjTy0fpXX2mZ Gy1DeGH7iZnapCCKlVg5ohtDpP3yg6HJgiwRB8pBEwHHxGeHrenrerLHCVQlCVlzz73u92xCeOpdM ZDzBRbYg==; Received: from [223.233.66.62] (helo=localhost.localdomain) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim) id 1uCcWg-004fhg-Ha; Wed, 07 May 2025 13:05:17 +0200 From: Bhupesh To: akpm@linux-foundation.org Cc: bhupesh@igalia.com, kernel-dev@igalia.com, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, oliver.sang@intel.com, lkp@intel.com, laoar.shao@gmail.com, pmladek@suse.com, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, arnaldo.melo@gmail.com, alexei.starovoitov@gmail.com, andrii.nakryiko@gmail.com, mirq-linux@rere.qmqm.pl, peterz@infradead.org, willy@infradead.org, david@redhat.com, viro@zeniv.linux.org.uk, keescook@chromium.org, ebiederm@xmission.com, brauner@kernel.org, jack@suse.cz, mingo@redhat.com, juri.lelli@redhat.com, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com Subject: [PATCH v3 3/3] exec: Add support for 64 byte 'tsk->real_comm' Date: Wed, 7 May 2025 16:34:44 +0530 Message-Id: <20250507110444.963779-4-bhupesh@igalia.com> X-Mailer: git-send-email 2.38.1 In-Reply-To: <20250507110444.963779-1-bhupesh@igalia.com> References: <20250507110444.963779-1-bhupesh@igalia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Historically due to the 16-byte length of TASK_COMM_LEN, the users of 'tsk->comm' are restricted to use a fixed-size target buffer also of TASK_COMM_LEN for 'memcpy()' like use-cases. To fix the same, Linus suggested in [1] that we can add the following union inside 'task_struct': union { char comm[TASK_COMM_LEN]; char real_comm[REAL_TASK_COMM_LEN]; }; and then modify '__set_task_comm()' to pass 'tsk->real_comm' to the existing users. This would mean that: (1) The old common pattern of just printing with '%s' and tsk->comm would just continue to work (as it is): pr_alert("BUG: Bad page state in process %s pfn:%05lx\n", current->comm, page_to_pfn(page)); (2) And, the memcpy() users of 'tsk->comm' would need to be made more stable by ensuring that the destination buffer always has a closing NUL character (done already in the preceding patch in this series). So, eventually: - users who want the existing 'TASK_COMM_LEN' behavior will get it (existing ABIs would continue to work), - users who just print out 'tsk->comm' as a string will get the longer new "real comm", - users who do 'sizeof(->comm)' will continue to get the old value because of the union. [1]. https://lore.kernel.org/all/CAHk-=3DwjAmmHUg6vho1KjzQi2=3DpsR30+CogFd4= aXrThr2gsiS4g@mail.gmail.com Signed-off-by: Bhupesh --- fs/exec.c | 6 +++--- include/linux/sched.h | 8 ++++++-- 2 files changed, 9 insertions(+), 5 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 8e4ea5f1e64c..2b2f2dacc013 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1190,11 +1190,11 @@ static int unshare_sighand(struct task_struct *me) */ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec) { - size_t len =3D min(strlen(buf), sizeof(tsk->comm) - 1); + size_t len =3D min(strlen(buf), sizeof(tsk->real_comm) - 1); =20 trace_task_rename(tsk, buf); - memcpy(tsk->comm, buf, len); - memset(&tsk->comm[len], 0, sizeof(tsk->comm) - len); + memcpy(tsk->real_comm, buf, len); + memset(&tsk->real_comm[len], 0, sizeof(tsk->real_comm) - len); perf_event_comm(tsk, exec); } =20 diff --git a/include/linux/sched.h b/include/linux/sched.h index cb219c6db179..2744d90badf1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -317,6 +317,7 @@ struct user_event_mm; */ enum { TASK_COMM_LEN =3D 16, + REAL_TASK_COMM_LEN =3D 64, }; =20 extern void sched_tick(void); @@ -1162,7 +1163,10 @@ struct task_struct { * - logic inside set_task_comm() will ensure it is always NUL-terminat= ed and * zero-padded */ - char comm[TASK_COMM_LEN]; + union { + char comm[TASK_COMM_LEN]; + char real_comm[REAL_TASK_COMM_LEN]; + }; =20 struct nameidata *nameidata; =20 @@ -2005,7 +2009,7 @@ extern void __set_task_comm(struct task_struct *tsk, = const char *from, bool exec */ #define get_task_comm(buf, tsk) ({ \ BUILD_BUG_ON(sizeof(buf) < TASK_COMM_LEN); \ - strscpy_pad(buf, (tsk)->comm); \ + strscpy_pad(buf, (tsk)->real_comm); \ buf; \ }) =20 --=20 2.38.1