Date:   Wed, 29 Sep 2021 11:09:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     akpm@...ux-foundation.org, pmladek@...e.com, peterz@...radead.org,
        valentin.schneider@....com, mathieu.desnoyers@...icios.com,
        qiang.zhang@...driver.com, robdclark@...omium.org,
        viro@...iv.linux.org.uk, christian@...uner.io,
        dietmar.eggemann@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] kernel: replace sizeof(task->comm) with TASK_COMM_LEN

On Wed, Sep 29, 2021 at 11:50:32AM +0000, Yafang Shao wrote:
> We can use TASK_COMM_LEN directly instread of sizeof(task->comm).

This change makes sense if we accept performing allocation for
task->comm, but I don't think that's a good idea. I'll reply to those
patches...

> This patch also replace strlcpy with strscpy, to fix the warning by
> checkpatch -
> WARNING: Prefer strscpy over strlcpy - see: https://lore.kernel.org/r/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/

I like this part of the patch, though! :)

-Kees

> 
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
>  arch/ia64/kernel/mca.c         | 6 +++---
>  drivers/block/drbd/drbd_main.c | 2 +-
>  drivers/hwtracing/stm/core.c   | 2 +-
>  drivers/tty/tty_audit.c        | 2 +-
>  fs/exec.c                      | 2 +-
>  kernel/audit.c                 | 4 ++--
>  kernel/auditsc.c               | 4 ++--
>  kernel/capability.c            | 4 ++--
>  kernel/futex.c                 | 2 +-
>  kernel/sys.c                   | 2 +-
>  kernel/trace/blktrace.c        | 2 +-
>  security/lsm_audit.c           | 4 ++--
>  security/selinux/selinuxfs.c   | 2 +-
>  security/yama/yama_lsm.c       | 2 +-
>  sound/core/oss/pcm_oss.c       | 2 +-
>  15 files changed, 21 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/ia64/kernel/mca.c b/arch/ia64/kernel/mca.c
> index e628a88607bb..4ee86e91ff5e 100644
> --- a/arch/ia64/kernel/mca.c
> +++ b/arch/ia64/kernel/mca.c
> @@ -875,7 +875,7 @@ copy_reg(const u64 *fr, u64 fnat, unsigned long *tr, unsigned long *tnat)
>  static void
>  ia64_mca_modify_comm(const struct task_struct *previous_current)
>  {
> -	char *p, comm[sizeof(current->comm)];
> +	char *p, comm[TASK_COMM_LEN];
>  	if (previous_current->pid)
>  		snprintf(comm, sizeof(comm), "%s %d",
>  			current->comm, previous_current->pid);
> @@ -889,7 +889,7 @@ ia64_mca_modify_comm(const struct task_struct *previous_current)
>  			current->comm, l, previous_current->comm,
>  			task_thread_info(previous_current)->cpu);
>  	}
> -	memcpy(current->comm, comm, sizeof(current->comm));
> +	memcpy(current->comm, comm, TASK_COMM_LEN);
>  }
>  
>  static void
> @@ -1794,7 +1794,7 @@ format_mca_init_stack(void *mca_data, unsigned long offset,
>  	p->parent = p->real_parent = p->group_leader = p;
>  	INIT_LIST_HEAD(&p->children);
>  	INIT_LIST_HEAD(&p->sibling);
> -	strncpy(p->comm, type, sizeof(p->comm)-1);
> +	strncpy(p->comm, type, TASK_COMM_LEN-1);
>  }
>  
>  /* Caller prevents this from being called after init */
> diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
> index 55234a558e98..a7cf062e76ab 100644
> --- a/drivers/block/drbd/drbd_main.c
> +++ b/drivers/block/drbd/drbd_main.c
> @@ -306,7 +306,7 @@ static int drbd_thread_setup(void *arg)
>  	unsigned long flags;
>  	int retval;
>  
> -	snprintf(current->comm, sizeof(current->comm), "drbd_%c_%s",
> +	snprintf(current->comm, TASK_COMM_LEN, "drbd_%c_%s",
>  		 thi->name[0],
>  		 resource->name);
>  
> diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
> index 2712e699ba08..8ec0a34a9ba6 100644
> --- a/drivers/hwtracing/stm/core.c
> +++ b/drivers/hwtracing/stm/core.c
> @@ -631,7 +631,7 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
>  	 * point, try to use the task name and "default" policy entries.
>  	 */
>  	if (!stmf->output.nr_chans) {
> -		char comm[sizeof(current->comm)];
> +		char comm[TASK_COMM_LEN];
>  		char *ids[] = { comm, "default", NULL };
>  
>  		get_task_comm(comm, current);
> diff --git a/drivers/tty/tty_audit.c b/drivers/tty/tty_audit.c
> index ca7afd7b2716..b98b1aef5f6f 100644
> --- a/drivers/tty/tty_audit.c
> +++ b/drivers/tty/tty_audit.c
> @@ -69,7 +69,7 @@ static void tty_audit_log(const char *description, dev_t dev,
>  
>  	ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_TTY);
>  	if (ab) {
> -		char name[sizeof(current->comm)];
> +		char name[TASK_COMM_LEN];
>  
>  		audit_log_format(ab, "%s pid=%u uid=%u auid=%u ses=%u major=%d"
>  				 " minor=%d comm=", description, pid, uid,
> diff --git a/fs/exec.c b/fs/exec.c
> index a098c133d8d7..021c9dc727bc 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1224,7 +1224,7 @@ void __set_task_comm(struct task_struct *tsk, const char *buf, bool exec)
>  {
>  	task_lock(tsk);
>  	trace_task_rename(tsk, buf);
> -	strlcpy(tsk->comm, buf, sizeof(tsk->comm));
> +	strscpy(tsk->comm, buf, TASK_COMM_LEN);
>  	task_unlock(tsk);
>  	perf_event_comm(tsk, exec);
>  }
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 121d37e700a6..1fbd036e77be 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1549,7 +1549,7 @@ static void audit_log_multicast(int group, const char *op, int err)
>  {
>  	const struct cred *cred;
>  	struct tty_struct *tty;
> -	char comm[sizeof(current->comm)];
> +	char comm[TASK_COMM_LEN];
>  	struct audit_buffer *ab;
>  
>  	if (!audit_enabled)
> @@ -2192,7 +2192,7 @@ void audit_put_tty(struct tty_struct *tty)
>  void audit_log_task_info(struct audit_buffer *ab)
>  {
>  	const struct cred *cred;
> -	char comm[sizeof(current->comm)];
> +	char comm[TASK_COMM_LEN];
>  	struct tty_struct *tty;
>  
>  	if (!ab)
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 8dd73a64f921..295376d7d926 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -2595,7 +2595,7 @@ void __audit_log_nfcfg(const char *name, u8 af, unsigned int nentries,
>  		       enum audit_nfcfgop op, gfp_t gfp)
>  {
>  	struct audit_buffer *ab;
> -	char comm[sizeof(current->comm)];
> +	char comm[TASK_COMM_LEN];
>  
>  	ab = audit_log_start(audit_context(), gfp, AUDIT_NETFILTER_CFG);
>  	if (!ab)
> @@ -2616,7 +2616,7 @@ static void audit_log_task(struct audit_buffer *ab)
>  	kuid_t auid, uid;
>  	kgid_t gid;
>  	unsigned int sessionid;
> -	char comm[sizeof(current->comm)];
> +	char comm[TASK_COMM_LEN];
>  
>  	auid = audit_get_loginuid(current);
>  	sessionid = audit_get_sessionid(current);
> diff --git a/kernel/capability.c b/kernel/capability.c
> index 46a361dde042..4033ee837f63 100644
> --- a/kernel/capability.c
> +++ b/kernel/capability.c
> @@ -45,7 +45,7 @@ __setup("no_file_caps", file_caps_disable);
>  
>  static void warn_legacy_capability_use(void)
>  {
> -	char name[sizeof(current->comm)];
> +	char name[TASK_COMM_LEN];
>  
>  	pr_info_once("warning: `%s' uses 32-bit capabilities (legacy support in use)\n",
>  		     get_task_comm(name, current));
> @@ -69,7 +69,7 @@ static void warn_legacy_capability_use(void)
>  
>  static void warn_deprecated_v2(void)
>  {
> -	char name[sizeof(current->comm)];
> +	char name[TASK_COMM_LEN];
>  
>  	pr_info_once("warning: `%s' uses deprecated v2 capabilities in a way that may be insecure\n",
>  		     get_task_comm(name, current));
> diff --git a/kernel/futex.c b/kernel/futex.c
> index c15ad276fd15..6cd08156611e 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -1703,7 +1703,7 @@ static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
>  
>  	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
>  		if (oparg < 0 || oparg > 31) {
> -			char comm[sizeof(current->comm)];
> +			char comm[TASK_COMM_LEN];
>  			/*
>  			 * kill this print and return -EINVAL when userspace
>  			 * is sane again
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 8fdac0d90504..bea1120c5579 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -2265,7 +2265,7 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
>  		unsigned long, arg4, unsigned long, arg5)
>  {
>  	struct task_struct *me = current;
> -	unsigned char comm[sizeof(me->comm)];
> +	unsigned char comm[TASK_COMM_LEN];
>  	long error;
>  
>  	error = security_task_prctl(option, arg2, arg3, arg4, arg5);
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index c221e4c3f625..009f77ebda5a 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -124,7 +124,7 @@ static void trace_note_tsk(struct task_struct *tsk)
>  	spin_lock_irqsave(&running_trace_lock, flags);
>  	list_for_each_entry(bt, &running_trace_list, running_list) {
>  		trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm,
> -			   sizeof(tsk->comm), 0);
> +			   TASK_COMM_LEN, 0);
>  	}
>  	spin_unlock_irqrestore(&running_trace_lock, flags);
>  }
> diff --git a/security/lsm_audit.c b/security/lsm_audit.c
> index 5a5016ef43b0..eec54cb48845 100644
> --- a/security/lsm_audit.c
> +++ b/security/lsm_audit.c
> @@ -208,7 +208,7 @@ static inline void print_ipv4_addr(struct audit_buffer *ab, __be32 addr,
>  static void dump_common_audit_data(struct audit_buffer *ab,
>  				   struct common_audit_data *a)
>  {
> -	char comm[sizeof(current->comm)];
> +	char comm[TASK_COMM_LEN];
>  
>  	/*
>  	 * To keep stack sizes in check force programers to notice if they
> @@ -310,7 +310,7 @@ static void dump_common_audit_data(struct audit_buffer *ab,
>  		if (tsk) {
>  			pid_t pid = task_tgid_nr(tsk);
>  			if (pid) {
> -				char comm[sizeof(tsk->comm)];
> +				char comm[TASK_COMM_LEN];
>  				audit_log_format(ab, " opid=%d ocomm=", pid);
>  				audit_log_untrustedstring(ab,
>  				    memcpy(comm, tsk->comm, sizeof(comm)));
> diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
> index e4cd7cb856f3..e529db76502d 100644
> --- a/security/selinux/selinuxfs.c
> +++ b/security/selinux/selinuxfs.c
> @@ -752,7 +752,7 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf,
>  		goto out;
>  
>  	if (new_value) {
> -		char comm[sizeof(current->comm)];
> +		char comm[TASK_COMM_LEN];
>  
>  		memcpy(comm, current->comm, sizeof(comm));
>  		pr_warn_once("SELinux: %s (%d) set checkreqprot to 1. This is deprecated and will be rejected in a future kernel release.\n",
> diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
> index 06e226166aab..178d7a138e98 100644
> --- a/security/yama/yama_lsm.c
> +++ b/security/yama/yama_lsm.c
> @@ -75,7 +75,7 @@ static void report_access(const char *access, struct task_struct *target,
>  				struct task_struct *agent)
>  {
>  	struct access_report_info *info;
> -	char agent_comm[sizeof(agent->comm)];
> +	char agent_comm[TASK_COMM_LEN];
>  
>  	assert_spin_locked(&target->alloc_lock); /* for target->comm */
>  
> diff --git a/sound/core/oss/pcm_oss.c b/sound/core/oss/pcm_oss.c
> index 82a818734a5f..d541530236e1 100644
> --- a/sound/core/oss/pcm_oss.c
> +++ b/sound/core/oss/pcm_oss.c
> @@ -2460,7 +2460,7 @@ static int snd_task_name(struct task_struct *task, char *name, size_t size)
>  
>  	if (snd_BUG_ON(!task || !name || size < 2))
>  		return -EINVAL;
> -	for (idx = 0; idx < sizeof(task->comm) && idx + 1 < size; idx++)
> +	for (idx = 0; idx < TASK_COMM_LEN && idx + 1 < size; idx++)
>  		name[idx] = task->comm[idx];
>  	name[idx] = '\0';
>  	return 0;
> -- 
> 2.17.1
> 

-- 
Kees Cook

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