fs/attr.c patch

["Павел Самсонов" <pvsamsonov76@gmail.com>]

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From 07b6f881080fa18ac404054d43b99433275fe966 Mon Sep 17 00:00:00 2001
From: Pavel Samsonov <pvsamsonov76@gmail.com>
Date: Fri, 10 Sep 2021 14:53:39 +0300
Subject: [PATCH] Signed-off-by: Pavel Samsonov <pvsamsonov76@gmail.com>

The patch changes the argument of chown_ok, chgrp_ok ...
functions from inode to dentry.
---
 fs/attr.c | 45 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 37 insertions(+), 8 deletions(-)

diff --git a/fs/attr.c b/fs/attr.c
index 473d21b3a86d..de1898c19bde 100644
--- a/fs/attr.c
+++ b/fs/attr.c
@@ -21,7 +21,7 @@
 /**
  * chown_ok - verify permissions to chown inode
  * @mnt_userns:	user namespace of the mount @inode was found from
- * @inode:	inode to check permissions on
+ * @dentry:	dentry to check permissions on
  * @uid:	uid to chown @inode to
  *
  * If the inode has been found through an idmapped mount the user namespace of
@@ -31,9 +31,11 @@
  * performed on the raw inode simply passs init_user_ns.
  */
 static bool chown_ok(struct user_namespace *mnt_userns,
-		     const struct inode *inode,
+		     const struct dentry *dentry,
 		     kuid_t uid)
 {
+	struct inode *inode = d_inode(dentry);
+
 	kuid_t kuid = i_uid_into_mnt(mnt_userns, inode);
 	if (uid_eq(current_fsuid(), kuid) && uid_eq(uid, kuid))
 		return true;
@@ -48,7 +50,7 @@ static bool chown_ok(struct user_namespace *mnt_userns,
 /**
  * chgrp_ok - verify permissions to chgrp inode
  * @mnt_userns:	user namespace of the mount @inode was found from
- * @inode:	inode to check permissions on
+ * @dentry:	dentry to check permissions on
  * @gid:	gid to chown @inode to
  *
  * If the inode has been found through an idmapped mount the user namespace of
@@ -58,8 +60,10 @@ static bool chown_ok(struct user_namespace *mnt_userns,
  * performed on the raw inode simply passs init_user_ns.
  */
 static bool chgrp_ok(struct user_namespace *mnt_userns,
-		     const struct inode *inode, kgid_t gid)
+		     const struct dentry *dentry, kgid_t gid)
 {
+	struct inode *inode = d_inode(dentry);
+
 	kgid_t kgid = i_gid_into_mnt(mnt_userns, inode);
 	if (uid_eq(current_fsuid(), i_uid_into_mnt(mnt_userns, inode)) &&
 	    (in_group_p(gid) || gid_eq(gid, kgid)))
@@ -72,6 +76,27 @@ static bool chgrp_ok(struct user_namespace *mnt_userns,
 	return false;
 }
 
+/**
+ * fowner_ok - verify permissions to chmod inode
+ * @mnt_userns:	user namespace of the mount @inode was found from
+ * @dentry:	dentry to check permissions on
+ *
+ * If the inode has been found through an idmapped mount the user namespace of
+ * the vfsmount must be passed through @mnt_userns. This function will then
+ * take care to map the inode according to @mnt_userns before checking
+ * permissions. On non-idmapped mounts or if permission checking is to be
+ * performed on the raw inode simply passs init_user_ns.
+ */
+static bool fowner_ok(struct user_namespace *mnt_userns,
+			const struct dentry *dentry)
+{
+	struct inode *inode = d_inode(dentry);
+
+	if (inode_owner_or_capable(mnt_userns, inode))
+	    return true;
+	return false;
+}
+
 /**
  * setattr_prepare - check if attribute changes to a dentry are allowed
  * @mnt_userns:	user namespace of the mount the inode was found from
@@ -114,27 +139,31 @@ int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
 		goto kill_priv;
 
 	/* Make sure a caller can chown. */
-	if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, inode, attr->ia_uid))
+	if ((ia_valid & ATTR_UID) && !chown_ok(mnt_userns, dentry, attr->ia_uid))
 		return -EPERM;
 
 	/* Make sure caller can chgrp. */
-	if ((ia_valid & ATTR_GID) && !chgrp_ok(mnt_userns, inode, attr->ia_gid))
+	if ((ia_valid & ATTR_GID) && !chgrp_ok(mnt_userns, dentry, attr->ia_gid))
 		return -EPERM;
 
 	/* Make sure a caller can chmod. */
 	if (ia_valid & ATTR_MODE) {
-		if (!inode_owner_or_capable(mnt_userns, inode))
+		if (!fowner_ok(mnt_userns, dentry))
 			return -EPERM;
 		/* Also check the setgid bit! */
                if (!in_group_p((ia_valid & ATTR_GID) ? attr->ia_gid :
                                 i_gid_into_mnt(mnt_userns, inode)) &&
                     !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
 			attr->ia_mode &= ~S_ISGID;
+		/* Also check the setuid bit! */
+		if (!(capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID) ||
+		     uid_eq(current_fsuid(), inode->i_uid)))
+			attr->ia_mode &= ~S_ISUID;
 	}
 
 	/* Check for setting the inode time. */
 	if (ia_valid & (ATTR_MTIME_SET | ATTR_ATIME_SET | ATTR_TIMES_SET)) {
-		if (!inode_owner_or_capable(mnt_userns, inode))
+		if (!fowner_ok(mnt_userns, dentry))
 			return -EPERM;
 	}
 
-- 
2.30.2