Re: [PATCH] lib/string_helpers: Use the given gfp flag when allocating memory

[Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>]

Le 17/01/2022 à 16:42, Michal Hocko a écrit :
> On Mon 17-01-22 10:51:59, Michal Hocko wrote:
> > On Sun 16-01-22 13:49:22, Christophe JAILLET wrote:
> > > kstrdup_quotable_cmdline() is given a gfp flag that is passed and used for
> > > memory allocation in kstrdup_quotable() just a few lines below.
> > >
> > > It looks reasonable to use this gfp value for the buffer allocated and
> > > freed in kstrdup_quotable_cmdline() as well.
> > >
> > > Fixes: 0ee931c4e31a ("mm: treewide: remove GFP_TEMPORARY allocation flag")
> >
> > I do not think this commit is changing much here. It just replaces
> > GFP_TEMPORARY with GFP_KERNEL so the code has ignored the gfp mask even
> > before that change.
> >
> > All existing callers of kstrdup_quotable_cmdline use GFP_KERNEL so would
> > it make more sense to simply drop the gfp argument altogether and use
> > GFP_KERNEL internally?
> >
> > Normally it is better to have a full control of the allocation mask but
> > if we have any non-GFP_KERNEL caller then I would rather have the
> > argument added and the function checked whether all internal paths are
> > gfp mask aware.
>
> In other words something like this:

For me, this is just fine.
This looks more consistant this way and (slighly) simplify the few callers.

CJ


> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index 2c46cd968ac4..44fde4b537f1 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -376,7 +376,7 @@ static void recover_worker(struct kthread_work *work)
>   		task = get_pid_task(submit->pid, PIDTYPE_PID);
>   		if (task) {
>   			comm = kstrdup(task->comm, GFP_KERNEL);
> -			cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
> +			cmd = kstrdup_quotable_cmdline(task);
>   			put_task_struct(task);
>   		}
>   
> @@ -467,7 +467,7 @@ static void fault_worker(struct kthread_work *work)
>   		task = get_pid_task(submit->pid, PIDTYPE_PID);
>   		if (task) {
>   			comm = kstrdup(task->comm, GFP_KERNEL);
> -			cmd = kstrdup_quotable_cmdline(task, GFP_KERNEL);
> +			cmd = kstrdup_quotable_cmdline(task);
>   			put_task_struct(task);
>   		}
>   
> diff --git a/include/linux/string_helpers.h b/include/linux/string_helpers.h
> index 4ba39e1403b2..7a67eee8bd0f 100644
> --- a/include/linux/string_helpers.h
> +++ b/include/linux/string_helpers.h
> @@ -97,8 +97,8 @@ static inline void string_lower(char *dst, const char *src)
>   }
>   
>   char *kstrdup_quotable(const char *src, gfp_t gfp);
> -char *kstrdup_quotable_cmdline(struct task_struct *task, gfp_t gfp);
> -char *kstrdup_quotable_file(struct file *file, gfp_t gfp);
> +char *kstrdup_quotable_cmdline(struct task_struct *task);
> +char *kstrdup_quotable_file(struct file *file);
>   
>   void kfree_strarray(char **array, size_t n);
>   
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index d5d008f5b1d9..267e142c7e13 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -618,12 +618,13 @@ EXPORT_SYMBOL_GPL(kstrdup_quotable);
>    * command line, with inter-argument NULLs replaced with spaces,
>    * and other special characters escaped.
>    */
> -char *kstrdup_quotable_cmdline(struct task_struct *task, gfp_t gfp)
> +char *kstrdup_quotable_cmdline(struct task_struct *task)
>   {
> +	gfp_t gfp = GFP_KERNEL;
>   	char *buffer, *quoted;
>   	int i, res;
>   
> -	buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
> +	buffer = kmalloc(PAGE_SIZE, gfp);
>   	if (!buffer)
>   		return NULL;
>   
> @@ -651,15 +652,16 @@ EXPORT_SYMBOL_GPL(kstrdup_quotable_cmdline);
>    * with special characters escaped, able to be safely logged. If
>    * there is an error, the leading character will be "<".
>    */
> -char *kstrdup_quotable_file(struct file *file, gfp_t gfp)
> +char *kstrdup_quotable_file(struct file *file)
>   {
> +	gfp_t gfp = GFP_KERNEL;
>   	char *temp, *pathname;
>   
>   	if (!file)
>   		return kstrdup("<unknown>", gfp);
>   
>   	/* We add 11 spaces for ' (deleted)' to be appended */
> -	temp = kmalloc(PATH_MAX + 11, GFP_KERNEL);
> +	temp = kmalloc(PATH_MAX + 11, gfp);
>   	if (!temp)
>   		return kstrdup("<no_memory>", gfp);
>   
> diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
> index b12f7d986b1e..79322ba89913 100644
> --- a/security/loadpin/loadpin.c
> +++ b/security/loadpin/loadpin.c
> @@ -23,8 +23,8 @@ static void report_load(const char *origin, struct file *file, char *operation)
>   {
>   	char *cmdline, *pathname;
>   
> -	pathname = kstrdup_quotable_file(file, GFP_KERNEL);
> -	cmdline = kstrdup_quotable_cmdline(current, GFP_KERNEL);
> +	pathname = kstrdup_quotable_file(file);
> +	cmdline = kstrdup_quotable_cmdline(current);
>   
>   	pr_notice("%s %s obj=%s%s%s pid=%d cmdline=%s%s%s\n",
>   		  origin, operation,
> diff --git a/security/yama/yama_lsm.c b/security/yama/yama_lsm.c
> index 06e226166aab..c87a41304b6c 100644
> --- a/security/yama/yama_lsm.c
> +++ b/security/yama/yama_lsm.c
> @@ -54,8 +54,8 @@ static void __report_access(struct callback_head *work)
>   		container_of(work, struct access_report_info, work);
>   	char *target_cmd, *agent_cmd;
>   
> -	target_cmd = kstrdup_quotable_cmdline(info->target, GFP_KERNEL);
> -	agent_cmd = kstrdup_quotable_cmdline(info->agent, GFP_KERNEL);
> +	target_cmd = kstrdup_quotable_cmdline(info->target);
> +	agent_cmd = kstrdup_quotable_cmdline(info->agent);
>   
>   	pr_notice_ratelimited(
>   		"ptrace %s of \"%s\"[%d] was attempted by \"%s\"[%d]\n",