Re: [PATCH] procfs: Fix error handling of proc_register()

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 16 Oct 2014 16:46:02 -0400 Debabrata Banerjee <dbanerje@akamai.com> wrote:

> 	I don't see why this should print warnings at all instead of properly
> 	unrolling allocations and returning an appropriate error. It's actually
> 	leaking resources currently.

I think the warnings are useful - a duplicate name in /proc is a
significant kernel bug and we'll want to know precisely what caused it
and get it fixed up quickly.  So let's keep that bit.

> --- a/fs/proc/generic.c
> +++ b/fs/proc/generic.c
> @@ -304,6 +304,7 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
>  		dp->proc_iops = &proc_file_inode_operations;
>  	} else {
>  		WARN_ON(1);
> +		proc_free_inum(dp->low_ino);
>  		return -EINVAL;
>  	}
>  
> @@ -311,9 +312,13 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
>  
>  	for (tmp = dir->subdir; tmp; tmp = tmp->next)
>  		if (strcmp(tmp->name, dp->name) == 0) {
> -			WARN(1, "proc_dir_entry '%s/%s' already registered\n",
> -				dir->name, dp->name);
> -			break;
> +			spin_unlock(&proc_subdir_lock);
> +
> +			if (S_ISDIR(dp->mode))
> +				dir->nlink--;
> +
> +			proc_free_inum(dp->low_ino);
> +			return -EEXIST;
>  		}

Your patch conflicts somewhat with Nicolas's "fs/proc: use a rb tree for
the directory entries".  Here's what I ended up with:



From: Debabrata Banerjee <dbanerje@akamai.com>
Subject: procfs: fix error handling of proc_register()

proc_register() error paths are leaking inodes and directory refcounts.

Signed-off-by: Debabrata Banerjee <dbanerje@akamai.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/proc/generic.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff -puN fs/proc/generic.c~procfs-fix-error-handling-of-proc_register fs/proc/generic.c
--- a/fs/proc/generic.c~procfs-fix-error-handling-of-proc_register
+++ a/fs/proc/generic.c
@@ -369,14 +369,21 @@ static int proc_register(struct proc_dir
 		dp->proc_iops = &proc_file_inode_operations;
 	} else {
 		WARN_ON(1);
+		proc_free_inum(dp->low_ino);
 		return -EINVAL;
 	}
 
 	spin_lock(&proc_subdir_lock);
 	dp->parent = dir;
-	if (pde_subdir_insert(dir, dp) == false)
+	if (pde_subdir_insert(dir, dp) == false) {
 		WARN(1, "proc_dir_entry '%s/%s' already registered\n",
 		     dir->name, dp->name);
+		spin_unlock(&proc_subdir_lock);
+		if (S_ISDIR(dp->mode))
+			dir->nlink--;
+		proc_free_inum(dp->low_ino);
+		return -EEXIST;
+	}
 	spin_unlock(&proc_subdir_lock);
 
 	return 0;
_