linux-kernel - Re: bpfilter logging write errors in dmesg

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Message-ID: <20200730070948.ysjruvwl4vjobwus@wittgenstein>
Date:   Thu, 30 Jul 2020 09:09:48 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: bpfilter logging write errors in dmesg

On Mon, Jul 27, 2020 at 04:50:13PM +0200, Christoph Hellwig wrote:
> Strange.  Can you add this additional debugging patch:

Sorry Christoph,

didn't mean to leave you waiting. I got pulled into other stuff.

Christian

> 
> diff --git a/fs/read_write.c b/fs/read_write.c
> index 4fb797822567a6..d0a8ada1efd954 100644
> --- a/fs/read_write.c
> +++ b/fs/read_write.c
> @@ -369,8 +369,10 @@ int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t
>  	int retval = -EINVAL;
>  
>  	inode = file_inode(file);
> -	if (unlikely((ssize_t) count < 0))
> +	if (unlikely((ssize_t) count < 0)) {
> +		printk("count invalid: %zd\n", count);
>  		return retval;
> +	}
>  
>  	/*
>  	 * ranged mandatory locking does not apply to streams - it makes sense
> @@ -380,25 +382,35 @@ int rw_verify_area(int read_write, struct file *file, const loff_t *ppos, size_t
>  		loff_t pos = *ppos;
>  
>  		if (unlikely(pos < 0)) {
> -			if (!unsigned_offsets(file))
> +			if (!unsigned_offsets(file)) {
> +				printk("pos invalid: %lld\n", pos);
>  				return retval;
> +			}
>  			if (count >= -pos) /* both values are in 0..LLONG_MAX */
>  				return -EOVERFLOW;
>  		} else if (unlikely((loff_t) (pos + count) < 0)) {
> -			if (!unsigned_offsets(file))
> +			if (!unsigned_offsets(file)) {
> +				printk("pos+count invalid: %lld, %zd\n", pos, count);
>  				return retval;
> +			}
>  		}
>  
>  		if (unlikely(inode->i_flctx && mandatory_lock(inode))) {
>  			retval = locks_mandatory_area(inode, file, pos, pos + count - 1,
>  					read_write == READ ? F_RDLCK : F_WRLCK);
> -			if (retval < 0)
> +			if (retval < 0) {
> +				if (retval == -EINVAL)
> +					printk("locks_mandatory_area\n");
>  				return retval;
> +			}
>  		}
>  	}
>  
> -	return security_file_permission(file,
> +	retval = security_file_permission(file,
>  				read_write == READ ? MAY_READ : MAY_WRITE);
> +	if (retval == -EINVAL)
> +		printk("security_file_permission\n");
> +	return retval;
>  }
>  
>  static ssize_t new_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos)