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-rw-r--r--fs/attr.c28
-rw-r--r--fs/internal.h6
2 files changed, 34 insertions, 0 deletions
diff --git a/fs/attr.c b/fs/attr.c
index e508b3caae76..085322536127 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -20,6 +20,34 @@
#include "internal.h"
+/**
+ * setattr_should_drop_sgid - determine whether the setgid bit needs to be
+ * removed
+ * @mnt_userns: user namespace of the mount @inode was found from
+ * @inode: inode to check
+ *
+ * This function determines whether the setgid bit needs to be removed.
+ * We retain backwards compatibility and require setgid bit to be removed
+ * unconditionally if S_IXGRP is set. Otherwise we have the exact same
+ * requirements as setattr_prepare() and setattr_copy().
+ *
+ * Return: ATTR_KILL_SGID if setgid bit needs to be removed, 0 otherwise.
+ */
+int setattr_should_drop_sgid(struct user_namespace *mnt_userns,
+ const struct inode *inode)
+{
+ umode_t mode = inode->i_mode;
+
+ if (!(mode & S_ISGID))
+ return 0;
+ if (mode & S_IXGRP)
+ return ATTR_KILL_SGID;
+ if (!in_group_or_capable(mnt_userns, inode,
+ i_gid_into_vfsgid(mnt_userns, inode)))
+ return ATTR_KILL_SGID;
+ return 0;
+}
+
/*
* The logic we want is
*
diff --git a/fs/internal.h b/fs/internal.h
index 1de39bbc9ddd..771b0468d70c 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -236,3 +236,9 @@ int do_setxattr(struct user_namespace *mnt_userns, struct dentry *dentry,
struct xattr_ctx *ctx);
ssize_t __kernel_write_iter(struct file *file, struct iov_iter *from, loff_t *pos);
+
+/*
+ * fs/attr.c
+ */
+int setattr_should_drop_sgid(struct user_namespace *mnt_userns,
+ const struct inode *inode);