[JFFS2] Handle inodes with only a single metadata node with non-zero isize

This should never happen unless there's corruption on the medium and the
actual data nodes go missing. But the failure mode (an oops when we assume
the fragtree isn't empty and go looking for its last node) isn't useful.
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

fs/jffs2/nodelist.c

@@ -52,7 +52,7 @@ void jffs2_add_fd_to_list(struct jffs2_sb_info *c, struct jffs2_full_dirent *new
 	*prev = new;
 }
 
-void jffs2_truncate_fragtree(struct jffs2_sb_info *c, struct rb_root *list, uint32_t size)
+uint32_t jffs2_truncate_fragtree(struct jffs2_sb_info *c, struct rb_root *list, uint32_t size)
 {
 	struct jffs2_node_frag *frag = jffs2_lookup_node_frag(list, size);
 
@@ -74,18 +74,24 @@ void jffs2_truncate_fragtree(struct jffs2_sb_info *c, struct rb_root *list, uint
 	}
 
 	if (size == 0)
-		return;
+		return 0;
 
-	/*
-	 * If the last fragment starts at the RAM page boundary, it is
-	 * REF_PRISTINE irrespective of its size.
-	 */
 	frag = frag_last(list);
+
+	/* Sanity check for truncation to longer than we started with... */
+	if (!frag)
+		return 0;
+	if (frag->ofs + frag->size < size)
+		return frag->ofs + frag->size;
+
+	/* If the last fragment starts at the RAM page boundary, it is
+	 * REF_PRISTINE irrespective of its size. */
 	if (frag->node && (frag->ofs & (PAGE_CACHE_SIZE - 1)) == 0) {
 		dbg_fragtree2("marking the last fragment 0x%08x-0x%08x REF_PRISTINE.\n",
 			frag->ofs, frag->ofs + frag->size);
 		frag->node->raw->flash_offset = ref_offset(frag->node->raw) | REF_PRISTINE;
 	}
+	return size;
 }
 
 static void jffs2_obsolete_node_frag(struct jffs2_sb_info *c,

fs/jffs2/nodelist.h

@@ -362,7 +362,7 @@ struct rb_node *rb_next(struct rb_node *);
 struct rb_node *rb_prev(struct rb_node *);
 void rb_replace_node(struct rb_node *victim, struct rb_node *new, struct rb_root *root);
 int jffs2_add_full_dnode_to_inode(struct jffs2_sb_info *c, struct jffs2_inode_info *f, struct jffs2_full_dnode *fn);
-void jffs2_truncate_fragtree (struct jffs2_sb_info *c, struct rb_root *list, uint32_t size);
+uint32_t jffs2_truncate_fragtree (struct jffs2_sb_info *c, struct rb_root *list, uint32_t size);
 struct jffs2_raw_node_ref *jffs2_link_node_ref(struct jffs2_sb_info *c,
 					       struct jffs2_eraseblock *jeb,
 					       uint32_t ofs, uint32_t len,

fs/jffs2/readinode.c

@@ -1132,7 +1132,7 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
 					struct jffs2_raw_inode *latest_node)
 {
 	struct jffs2_readinode_info rii;
-	uint32_t crc;
+	uint32_t crc, new_size;
 	size_t retlen;
 	int ret;
 
@@ -1233,7 +1233,12 @@ static int jffs2_do_read_inode_internal(struct jffs2_sb_info *c,
 
 	case S_IFREG:
 		/* If it was a regular file, truncate it to the latest node's isize */
-		jffs2_truncate_fragtree(c, &f->fragtree, je32_to_cpu(latest_node->isize));
+		new_size = jffs2_truncate_fragtree(c, &f->fragtree, je32_to_cpu(latest_node->isize));
+		if (new_size != je32_to_cpu(latest_node->isize)) {
+			JFFS2_WARNING("Truncating ino #%u to %d bytes failed because it only had %d bytes to start with!\n",
+				      f->inocache->ino, je32_to_cpu(latest_node->isize), new_size);
+			latest_node->isize = cpu_to_je32(new_size);
+		}
 		break;
 
 	case S_IFLNK: