nilfs2: treat missing sufile header block as metadata corruption

Patch series "nilfs2: prevent unexpected ENOENT propagation".

This series fixes potential issues where the result code -ENOENT, which is
returned internally when a metadata file operation encouters a hole block,
is exposed to user space without being properly handled.

Several issues with the same cause leading to hangs or WARN_ON check
failures have been reported by syzbot and fixed each time in the past. 
This collectively fixes the missing -ENOENT conversions that do not cause
stability issues and are not covered by syzbot.


This patch (of 5):

The sufile, a metadata file that holds metadata for segment management,
has statistical information in its first block, but if reading this block
fails, it receives the internal code -ENOENT and returns it unchanged to
the callers.

To prevent this -ENOENT from being propagated to system calls, if reading
the header block fails, return -EIO (or -EINVAL depending on the context)
instead.

Link: https://lkml.kernel.org/r/20240821154627.11848-1-konishi.ryusuke@gmail.com
Link: https://lkml.kernel.org/r/20240821154627.11848-2-konishi.ryusuke@gmail.comSigned-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nilfs2/sufile.c

@@ -79,10 +79,17 @@ nilfs_sufile_block_get_segment_usage(const struct inode *sufile, __u64 segnum,
 		NILFS_MDT(sufile)->mi_entry_size;
 }
 
-static inline int nilfs_sufile_get_header_block(struct inode *sufile,
-						struct buffer_head **bhp)
+static int nilfs_sufile_get_header_block(struct inode *sufile,
+					 struct buffer_head **bhp)
 {
-	return nilfs_mdt_get_block(sufile, 0, 0, NULL, bhp);
+	int err = nilfs_mdt_get_block(sufile, 0, 0, NULL, bhp);
+
+	if (unlikely(err == -ENOENT)) {
+		nilfs_error(sufile->i_sb,
+			    "missing header block in segment usage metadata");
+		err = -EIO;
+	}
+	return err;
 }
 
 static inline int
@@ -1237,9 +1244,15 @@ int nilfs_sufile_read(struct super_block *sb, size_t susize,
 	if (err)
 		goto failed;
 
-	err = nilfs_sufile_get_header_block(sufile, &header_bh);
-	if (err)
+	err = nilfs_mdt_get_block(sufile, 0, 0, NULL, &header_bh);
+	if (unlikely(err)) {
+		if (err == -ENOENT) {
+			nilfs_err(sb,
+				  "missing header block in segment usage metadata");
+			err = -EINVAL;
+		}
 		goto failed;
+	}
 
 	sui = NILFS_SUI(sufile);
 	kaddr = kmap_local_page(header_bh->b_page);