[PATCH 2/2] jffs2: fix can't set rp_size to zero during remounting

[Zhe Li <lizhe67@huawei.com>]

From: lizhe <lizhe67@huawei.com>

Set rp_size to zero will be ignore during remounting.

The method to identify whether we input a remounting option of
rp_size is to check if the rp_size input is zero. It can not work
well if we pass "rp_size=0".

This patch add a bool variable "set_rp_size" to fix this problem.

By the way, the problem of NULL pointer dereference in rp_size
fs option parsing showed at
https://lore.kernel.org/linux-mtd/20201012131204.59102-1-jamie@nuviainc.com/T/#u
should be applyed before this patch to make sure it works well.

Reported-by: Jubin Zhong <zhongjubin@huawei.com>
Signed-off-by: lizhe <lizhe67@huawei.com>
---
 fs/jffs2/jffs2_fs_sb.h | 1 +
 fs/jffs2/super.c       | 7 +++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/jffs2/jffs2_fs_sb.h b/fs/jffs2/jffs2_fs_sb.h
index 778275f48a87..5a7091746f68 100644
--- a/fs/jffs2/jffs2_fs_sb.h
+++ b/fs/jffs2/jffs2_fs_sb.h
@@ -38,6 +38,7 @@ struct jffs2_mount_opts {
 	 * users. This is implemented simply by means of not allowing the
 	 * latter users to write to the file system if the amount if the
 	 * available space is less then 'rp_size'. */
+	bool set_rp_size;
 	unsigned int rp_size;
 };
 
diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
index 4fd297bdf0f3..c523adaca79f 100644
--- a/fs/jffs2/super.c
+++ b/fs/jffs2/super.c
@@ -88,7 +88,7 @@ static int jffs2_show_options(struct seq_file *s, struct dentry *root)
 
 	if (opts->override_compr)
 		seq_printf(s, ",compr=%s", jffs2_compr_name(opts->compr));
-	if (opts->rp_size)
+	if (opts->set_rp_size)
 		seq_printf(s, ",rp_size=%u", opts->rp_size / 1024);
 
 	return 0;
@@ -206,6 +206,7 @@ static int jffs2_parse_param(struct fs_context *fc, struct fs_parameter *param)
 		if (opt > c->mtd->size)
 			return invalf(fc, "jffs2: Too large reserve pool specified, max is %llu KB",
 				      c->mtd->size / 1024);
+		c->mount_opts.set_rp_size = true;
 		c->mount_opts.rp_size = opt;
 		break;
 	default:
@@ -225,8 +226,10 @@ static inline void jffs2_update_mount_opts(struct fs_context *fc)
 		c->mount_opts.override_compr = new_c->mount_opts.override_compr;
 		c->mount_opts.compr = new_c->mount_opts.compr;
 	}
-	if (new_c->mount_opts.rp_size)
+	if (new_c->mount_opts.set_rp_size) {
+		c->mount_opts.set_rp_size = new_c->mount_opts.set_rp_size;
 		c->mount_opts.rp_size = new_c->mount_opts.rp_size;
+	}
 	mutex_unlock(&c->alloc_sem);
 }
 
-- 
2.12.3