[PATCH 2/2] ceph: don't keep a mon_addr= that failed to parse

[Yogesh Gaur <yogeshgaur.83@gmail.com>]

ceph_parse_mon_addr() stores the string in fsopt->mon_addr before handing
it to ceph_parse_mon_ips(), and then returns that function's error. So
after a mon_addr= that does not parse, fsconfig() reports the failure but
the mount context keeps the rejected string.

That matters because ceph_get_tree() uses fsopt->mon_addr as the "monitor
addresses were supplied" test:

	if (fsopt->new_dev_syntax && !fsopt->mon_addr)
		return invalfc(fc, "No monitor address");

Userspace is free to ignore the error from fsconfig(FSCONFIG_SET_STRING)
and go straight to FSCONFIG_CMD_CREATE. The check then passes on a value
that was rejected, and the mount continues with ceph_options::num_mon
still 0 - which is how syzbot reached the BUG_ON() in pick_new_mon()
fixed by the previous patch.

Parse first and commit only on success. A failed mon_addr= now leaves any
previously accepted value in place instead of replacing it with one that
does not parse.

Reported-by: syzbot+1dbed5969931c19d3eb5@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=1dbed5969931c19d3eb5
Fixes: 7b19b4db5add ("ceph: new device mount syntax")
Assisted-by: LLM
Signed-off-by: Yogesh Gaur <yogeshgaur.83@gmail.com>
---
 fs/ceph/super.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 72935f665f11..9e0aee8f33ff 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -394,13 +394,18 @@ static int ceph_parse_mon_addr(struct fs_parameter *param,
 {
 	struct ceph_parse_opts_ctx *pctx = fc->fs_private;
 	struct ceph_mount_options *fsopt = pctx->opts;
+	int ret;
+
+	ret = ceph_parse_mon_ips(param->string, strlen(param->string),
+				 pctx->copts, fc->log.log, '/');
+	if (ret)
+		return ret;
 
 	kfree(fsopt->mon_addr);
 	fsopt->mon_addr = param->string;
 	param->string = NULL;
 
-	return ceph_parse_mon_ips(fsopt->mon_addr, strlen(fsopt->mon_addr),
-				  pctx->copts, fc->log.log, '/');
+	return 0;
 }
 
 static int ceph_parse_mount_param(struct fs_context *fc,
-- 
2.55.0.windows.5