[PATCH v5 1/4] fs: move sgid strip operation from inode_init_owner into inode_sgid_strip

[Yang Xu <xuyang2018.jy@xxxxxxxxxxx>]

This has no functional change. Just create and export inode_sgid_strip
api for the subsequent patch. This function is used to strip inode's
S_ISGID mode when init a new inode.

Signed-off-by: Yang Xu <xuyang2018.jy@xxxxxxxxxxx>
---
v4-v5:
use umode_t return value instead of mode pointer
 fs/inode.c         | 23 +++++++++++++++++++----
 include/linux/fs.h |  2 ++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 9d9b422504d1..57130e4ef8b4 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2246,10 +2246,8 @@ void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
 		/* Directories are special, and always inherit S_ISGID */
 		if (S_ISDIR(mode))
 			mode |= S_ISGID;
-		else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
-			 !in_group_p(i_gid_into_mnt(mnt_userns, dir)) &&
-			 !capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
-			mode &= ~S_ISGID;
+		else
+			mode = inode_sgid_strip(mnt_userns, dir, mode);
 	} else
 		inode_fsgid_set(inode, mnt_userns);
 	inode->i_mode = mode;
@@ -2405,3 +2403,20 @@ struct timespec64 current_time(struct inode *inode)
 	return timestamp_truncate(now, inode);
 }
 EXPORT_SYMBOL(current_time);
+
+umode_t inode_sgid_strip(struct user_namespace *mnt_userns,
+			 const struct inode *dir, umode_t mode)
+{
+	if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
+		return mode;
+	if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
+		return mode;
+	if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
+		return mode;
+	if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
+		return mode;
+
+	mode &= ~S_ISGID;
+	return mode;
+}
+EXPORT_SYMBOL(inode_sgid_strip);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbde95387a23..532de76c9b91 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1897,6 +1897,8 @@ extern long compat_ptr_ioctl(struct file *file, unsigned int cmd,
 void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
 		      const struct inode *dir, umode_t mode);
 extern bool may_open_dev(const struct path *path);
+umode_t inode_sgid_strip(struct user_namespace *mnt_userns,
+			 const struct inode *dir, umode_t mode);
 
 /*
  * This is the "filldir" function type, used by readdir() to let
-- 
2.27.0