__proc_create() has limited dirent's max name length with 255, let's
add this limitation in proc_lookup_de(), so that it can return
-ENAMETOOLONG correctly instead of -ENOENT when stating a file which
has out-of-range name length.

Signed-off-by: Chao Yu <chao@kernel.org>
---
 fs/proc/generic.c  | 5 ++++-
 fs/proc/internal.h | 3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 587b91d9d998..5f52f20d5ed1 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -246,6 +246,9 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
 {
 	struct inode *inode;
 
+	if (dentry->d_name.len > PROC_NAME_LEN)
+		return ERR_PTR(-ENAMETOOLONG);
+
 	read_lock(&proc_subdir_lock);
 	de = pde_subdir_find(de, dentry->d_name.name, dentry->d_name.len);
 	if (de) {
@@ -402,7 +405,7 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 		goto out;
 	qstr.name = fn;
 	qstr.len = strlen(fn);
-	if (qstr.len == 0 || qstr.len >= 256) {
+	if (qstr.len == 0 || qstr.len > PROC_NAME_LEN) {
 		WARN(1, "name len %u\n", qstr.len);
 		return NULL;
 	}
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index b701d0207edf..7611bc684d9e 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -142,6 +142,9 @@ unsigned name_to_int(const struct qstr *qstr);
 /* Worst case buffer size needed for holding an integer. */
 #define PROC_NUMBUF 13
 
+/* Max name length of procfs dirent */
+#define PROC_NAME_LEN		255
+
 /*
  * array.c
  */
-- 
2.25.1

On Tue, Jan 10, 2023 at 11:21:12PM +0800, Chao Yu wrote:
> __proc_create() has limited dirent's max name length with 255, let's
> add this limitation in proc_lookup_de(), so that it can return
> -ENAMETOOLONG correctly instead of -ENOENT when stating a file which
> has out-of-range name length.

Both returns are correct and this is trading one errno for another.

> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -246,6 +246,9 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
>  {
>  	struct inode *inode;
>  
> +	if (dentry->d_name.len > PROC_NAME_LEN)
> +		return ERR_PTR(-ENAMETOOLONG);

On 2023/1/11 2:01, Alexey Dobriyan wrote:
> On Tue, Jan 10, 2023 at 11:21:12PM +0800, Chao Yu wrote:
>> __proc_create() has limited dirent's max name length with 255, let's
>> add this limitation in proc_lookup_de(), so that it can return
>> -ENAMETOOLONG correctly instead of -ENOENT when stating a file which
>> has out-of-range name length.
> 
> Both returns are correct and this is trading one errno for another.

Oh, but it looks ENOENT is a little bit ambiguity, it may indicate file name
length is valid for procfs, but the entry is not exist.

This change is trying to make lookup logic keeping align w/ most other
filesystems' behavior. Also it can avoid running into unneeded lookup logic
in proc_lookup_de() for such ENAMETOOLONG case.

How do you think? :)

Thanks,

> 
>> --- a/fs/proc/generic.c
>> +++ b/fs/proc/generic.c
>> @@ -246,6 +246,9 @@ struct dentry *proc_lookup_de(struct inode *dir, struct dentry *dentry,
>>   {
>>   	struct inode *inode;
>>   
>> +	if (dentry->d_name.len > PROC_NAME_LEN)
>> +		return ERR_PTR(-ENAMETOOLONG);