linux-kernel - Re: [PATCH] fs: proc: fix error return code of proc_map_files

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Date:   Tue, 9 Mar 2021 10:30:23 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     adobriyan@...il.com, christian@...uner.io, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, keescook@...omium.org,
        gladkov.alexey@...il.com, walken@...gle.com,
        bernd.edlinger@...mail.de, avagin@...il.com, deller@....de,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] fs: proc: fix error return code of
 proc_map_files_readdir()

On Tue, Mar 09, 2021 at 01:55:27AM -0800, Jia-Ju Bai wrote:
> When get_task_mm() returns NULL to mm, no error return code of
> proc_map_files_readdir() is assigned.
> To fix this bug, ret is assigned with -ENOENT in this case.
> 
> Fixes: f0c3b5093add ("[readdir] convert procfs")
> Reported-by: TOTE Robot <oslab@...nghua.edu.cn>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
> ---
>  fs/proc/base.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 3851bfcdba56..254cc6ac65fb 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -2332,8 +2332,10 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
>  		goto out_put_task;
>  
>  	mm = get_task_mm(task);
> -	if (!mm)
> +	if (!mm) {
> +		ret = -ENOENT;
>  		goto out_put_task;
> +	}
>  
>  	ret = mmap_read_lock_killable(mm);

Is there something in particular that makes you think that returning ENOENT is
the correct behavior in this case?  Try 'ls /proc/$pid/map_files' where pid is a
kernel thread; it's an empty directory, which is probably intentional.  Your
patch would change reading the directory to fail with ENOENT.

- Eric