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

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Message-ID: <20200727145013.GA2154@lst.de>
Date:   Mon, 27 Jul 2020 16:50:13 +0200
From:   Christoph Hellwig <hch@....de>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org
Subject: Re: bpfilter logging write errors in dmesg

Strange.  Can you add this additional debugging patch:

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)