Re: [PATCH v1] erofs: Fix state inconsistency when updating fsid/domain_id

[Gao Xiang]

Hi Baolin,

On 2026/1/6 10:55, Baolin Liu wrote:

From: Baolin Liu <liubao...@kylinos.cn>

When updating fsid or domain_id, the code frees the old pointer before
allocating a new one. If allocation fails, the pointer becomes NULL
while the old value is already freed, causing state inconsistency.

Fix by allocating the new value first, and only freeing the old value
on success.

Signed-off-by: Baolin Liu <liubao...@kylinos.cn>
---
  fs/erofs/super.c | 18 ++++++++++++------
  1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 937a215f626c..6e083d7e634c 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -509,16 +509,22 @@ static int erofs_fc_parse_param(struct fs_context *fc,
                break;
  #ifdef CONFIG_EROFS_FS_ONDEMAND
        case Opt_fsid:
-               kfree(sbi->fsid);
-               sbi->fsid = kstrdup(param->string, GFP_KERNEL);
-               if (!sbi->fsid)
+               char *new_fsid;

could you move

char *new_fsid, *new_domain_id;

to the beginning of `erofs_fc_parse_param()`
to avoid variable definitions in the switch statement?

or maybe just call it as:

char *newstr;

Thanks,
Gao Xiang

+
+               new_fsid = kstrdup(param->string, GFP_KERNEL);
+               if (!new_fsid)
                        return -ENOMEM;
+               kfree(sbi->fsid);
+               sbi->fsid = new_fsid;
                break;
        case Opt_domain_id:
-               kfree(sbi->domain_id);
-               sbi->domain_id = kstrdup(param->string, GFP_KERNEL);
-               if (!sbi->domain_id)
+               char *new_domain_id;
+
+               new_domain_id = kstrdup(param->string, GFP_KERNEL);
+               if (!new_domain_id)
                        return -ENOMEM;
+               kfree(sbi->domain_id);
+               sbi->domain_id = new_domain_id;
                break;
  #else
        case Opt_fsid: