Merge branch 'fs.ovl.setgid' into for-next

* fs.ovl.setgid:
  ovl: remove privs in ovl_fallocate()
  ovl: remove privs in ovl_copyfile()
  attr: use consistent sgid stripping checks
  attr: add setattr_should_drop_sgid()
  fs: move should_remove_suid()
  attr: add in_group_or_capable()

Documentation/trace/ftrace.rst

@@ -2940,7 +2940,7 @@ Produces::
               bash-1994  [000] ....  4342.324898: ima_get_action <-process_measurement
               bash-1994  [000] ....  4342.324898: ima_match_policy <-ima_get_action
               bash-1994  [000] ....  4342.324899: do_truncate <-do_last
-              bash-1994  [000] ....  4342.324899: should_remove_suid <-do_truncate
+              bash-1994  [000] ....  4342.324899: setattr_should_drop_suidgid <-do_truncate
               bash-1994  [000] ....  4342.324899: notify_change <-do_truncate
               bash-1994  [000] ....  4342.324900: current_fs_time <-notify_change
               bash-1994  [000] ....  4342.324900: current_kernel_time <-current_fs_time

fs/attr.c

@@ -18,6 +18,70 @@
 #include <linux/evm.h>
 #include <linux/ima.h>
 
+#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;
+}
+
+/**
+ * setattr_should_drop_suidgid - determine whether the set{g,u}id bit needs to
+ *                               be dropped
+ * @mnt_userns:	user namespace of the mount @inode was found from
+ * @inode:	inode to check
+ *
+ * This function determines whether the set{g,u}id bits need to be removed.
+ * If the setuid bit needs to be removed ATTR_KILL_SUID is returned. If the
+ * setgid bit needs to be removed ATTR_KILL_SGID is returned. If both
+ * set{g,u}id bits need to be removed the corresponding mask of both flags is
+ * returned.
+ *
+ * Return: A mask of ATTR_KILL_S{G,U}ID indicating which - if any - setid bits
+ * to remove, 0 otherwise.
+ */
+int setattr_should_drop_suidgid(struct user_namespace *mnt_userns,
+				struct inode *inode)
+{
+	umode_t mode = inode->i_mode;
+	int kill = 0;
+
+	/* suid always must be killed */
+	if (unlikely(mode & S_ISUID))
+		kill = ATTR_KILL_SUID;
+
+	kill |= setattr_should_drop_sgid(mnt_userns, inode);
+
+	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
+		return kill;
+
+	return 0;
+}
+EXPORT_SYMBOL(setattr_should_drop_suidgid);
+
 /**
  * chown_ok - verify permissions to chown inode
  * @mnt_userns:	user namespace of the mount @inode was found from
@@ -140,8 +204,7 @@ int setattr_prepare(struct user_namespace *mnt_userns, struct dentry *dentry,
 			vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
 
 		/* Also check the setgid bit! */
-		if (!vfsgid_in_group_p(vfsgid) &&
-		    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+		if (!in_group_or_capable(mnt_userns, inode, vfsgid))
 			attr->ia_mode &= ~S_ISGID;
 	}
 
@@ -251,9 +314,8 @@ void setattr_copy(struct user_namespace *mnt_userns, struct inode *inode,
 		inode->i_ctime = attr->ia_ctime;
 	if (ia_valid & ATTR_MODE) {
 		umode_t mode = attr->ia_mode;
-		vfsgid_t vfsgid = i_gid_into_vfsgid(mnt_userns, inode);
-		if (!vfsgid_in_group_p(vfsgid) &&
-		    !capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+		if (!in_group_or_capable(mnt_userns, inode,
+					 i_gid_into_vfsgid(mnt_userns, inode)))
 			mode &= ~S_ISGID;
 		inode->i_mode = mode;
 	}
@@ -375,7 +437,7 @@ int notify_change(struct user_namespace *mnt_userns, struct dentry *dentry,
 		}
 	}
 	if (ia_valid & ATTR_KILL_SGID) {
-		if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
+		if (mode & S_ISGID) {
 			if (!(ia_valid & ATTR_MODE)) {
 				ia_valid = attr->ia_valid |= ATTR_MODE;
 				attr->ia_mode = inode->i_mode;

fs/fuse/file.c

@@ -1313,7 +1313,7 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			return err;
 
 		if (fc->handle_killpriv_v2 &&
-		    should_remove_suid(file_dentry(file))) {
+		    setattr_should_drop_suidgid(&init_user_ns, file_inode(file))) {
 			goto writethrough;
 		}
 

fs/inode.c

@@ -1948,41 +1948,13 @@ void touch_atime(const struct path *path)
 }
 EXPORT_SYMBOL(touch_atime);
 
-/*
- * The logic we want is
- *
- *	if suid or (sgid and xgrp)
- *		remove privs
- */
-int should_remove_suid(struct dentry *dentry)
-{
-	umode_t mode = d_inode(dentry)->i_mode;
-	int kill = 0;
-
-	/* suid always must be killed */
-	if (unlikely(mode & S_ISUID))
-		kill = ATTR_KILL_SUID;
-
-	/*
-	 * sgid without any exec bits is just a mandatory locking mark; leave
-	 * it alone.  If some exec bits are set, it's a real sgid; kill it.
-	 */
-	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
-		kill |= ATTR_KILL_SGID;
-
-	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
-		return kill;
-
-	return 0;
-}
-EXPORT_SYMBOL(should_remove_suid);
-
 /*
  * Return mask of changes for notify_change() that need to be done as a
  * response to write or truncate. Return 0 if nothing has to be changed.
  * Negative value on error (change should be denied).
  */
-int dentry_needs_remove_privs(struct dentry *dentry)
+int dentry_needs_remove_privs(struct user_namespace *mnt_userns,
+			      struct dentry *dentry)
 {
 	struct inode *inode = d_inode(dentry);
 	int mask = 0;
@@ -1991,7 +1963,7 @@ int dentry_needs_remove_privs(struct dentry *dentry)
 	if (IS_NOSEC(inode))
 		return 0;
 
-	mask = should_remove_suid(dentry);
+	mask = setattr_should_drop_suidgid(mnt_userns, inode);
 	ret = security_inode_need_killpriv(dentry);
 	if (ret < 0)
 		return ret;
@@ -2023,7 +1995,7 @@ static int __file_remove_privs(struct file *file, unsigned int flags)
 	if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
 		return 0;
 
-	kill = dentry_needs_remove_privs(dentry);
+	kill = dentry_needs_remove_privs(file_mnt_user_ns(file), dentry);
 	if (kill < 0)
 		return kill;
 
@@ -2487,6 +2459,28 @@ struct timespec64 current_time(struct inode *inode)
 }
 EXPORT_SYMBOL(current_time);
 
+/**
+ * in_group_or_capable - check whether caller is CAP_FSETID privileged
+ * @mnt_userns: user namespace of the mount @inode was found from
+ * @inode:	inode to check
+ * @vfsgid:	the new/current vfsgid of @inode
+ *
+ * Check wether @vfsgid is in the caller's group list or if the caller is
+ * privileged with CAP_FSETID over @inode. This can be used to determine
+ * whether the setgid bit can be kept or must be dropped.
+ *
+ * Return: true if the caller is sufficiently privileged, false if not.
+ */
+bool in_group_or_capable(struct user_namespace *mnt_userns,
+			 const struct inode *inode, vfsgid_t vfsgid)
+{
+	if (vfsgid_in_group_p(vfsgid))
+		return true;
+	if (capable_wrt_inode_uidgid(mnt_userns, inode, CAP_FSETID))
+		return true;
+	return false;
+}
+
 /**
  * mode_strip_sgid - handle the sgid bit for non-directories
  * @mnt_userns: User namespace of the mount the inode was created from
@@ -2508,11 +2502,9 @@ umode_t mode_strip_sgid(struct user_namespace *mnt_userns,
 		return mode;
 	if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
 		return mode;
-	if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
+	if (in_group_or_capable(mnt_userns, dir,
+				i_gid_into_vfsgid(mnt_userns, dir)))
 		return mode;
-	if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
-		return mode;
-
 	return mode & ~S_ISGID;
 }
 EXPORT_SYMBOL(mode_strip_sgid);

fs/internal.h

@@ -150,7 +150,9 @@ extern int vfs_open(const struct path *, struct file *);
  * inode.c
  */
 extern long prune_icache_sb(struct super_block *sb, struct shrink_control *sc);
-extern int dentry_needs_remove_privs(struct dentry *dentry);
+int dentry_needs_remove_privs(struct user_namespace *, struct dentry *dentry);
+bool in_group_or_capable(struct user_namespace *mnt_userns,
+			 const struct inode *inode, vfsgid_t vfsgid);
 
 /*
  * fs-writeback.c
@@ -234,3 +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);

fs/ocfs2/file.c

@@ -1991,7 +1991,7 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 		}
 	}
 
-	if (file && should_remove_suid(file->f_path.dentry)) {
+	if (file && setattr_should_drop_suidgid(&init_user_ns, file_inode(file))) {
 		ret = __ocfs2_write_remove_suid(inode, di_bh);
 		if (ret) {
 			mlog_errno(ret);
@@ -2279,7 +2279,7 @@ static int ocfs2_prepare_inode_for_write(struct file *file,
 		 * inode. There's also the dinode i_size state which
 		 * can be lost via setattr during extending writes (we
 		 * set inode->i_size at the end of a write. */
-		if (should_remove_suid(dentry)) {
+		if (setattr_should_drop_suidgid(&init_user_ns, inode)) {
 			if (meta_level == 0) {
 				ocfs2_inode_unlock_for_extent_tree(inode,
 								   &di_bh,

fs/open.c

@@ -54,7 +54,7 @@ int do_truncate(struct user_namespace *mnt_userns, struct dentry *dentry,
 	}
 
 	/* Remove suid, sgid, and file capabilities on truncate too */
-	ret = dentry_needs_remove_privs(dentry);
+	ret = dentry_needs_remove_privs(mnt_userns, dentry);
 	if (ret < 0)
 		return ret;
 	if (ret)
@@ -723,10 +723,10 @@ int chown_common(const struct path *path, uid_t user, gid_t group)
 		return -EINVAL;
 	if ((group != (gid_t)-1) && !setattr_vfsgid(&newattrs, gid))
 		return -EINVAL;
-	if (!S_ISDIR(inode->i_mode))
-		newattrs.ia_valid |=
-			ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_KILL_PRIV;
 	inode_lock(inode);
+	if (!S_ISDIR(inode->i_mode))
+		newattrs.ia_valid |= ATTR_KILL_SUID | ATTR_KILL_PRIV |
+				     setattr_should_drop_sgid(mnt_userns, inode);
 	/* Continue to send actual fs values, not the mount values. */
 	error = security_path_chown(
 		path,

fs/overlayfs/file.c

@@ -517,9 +517,16 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len
 	const struct cred *old_cred;
 	int ret;
 
+	inode_lock(inode);
+	/* Update mode */
+	ovl_copyattr(inode);
+	ret = file_remove_privs(file);
+	if (ret)
+		goto out_unlock;
+
 	ret = ovl_real_fdget(file, &real);
 	if (ret)
-		return ret;
+		goto out_unlock;
 
 	old_cred = ovl_override_creds(file_inode(file)->i_sb);
 	ret = vfs_fallocate(real.file, mode, offset, len);
@@ -530,6 +537,9 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len
 
 	fdput(real);
 
+out_unlock:
+	inode_unlock(inode);
+
 	return ret;
 }
 
@@ -567,14 +577,23 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 	const struct cred *old_cred;
 	loff_t ret;
 
+	inode_lock(inode_out);
+	if (op != OVL_DEDUPE) {
+		/* Update mode */
+		ovl_copyattr(inode_out);
+		ret = file_remove_privs(file_out);
+		if (ret)
+			goto out_unlock;
+	}
+
 	ret = ovl_real_fdget(file_out, &real_out);
 	if (ret)
-		return ret;
+		goto out_unlock;
 
 	ret = ovl_real_fdget(file_in, &real_in);
 	if (ret) {
 		fdput(real_out);
-		return ret;
+		goto out_unlock;
 	}
 
 	old_cred = ovl_override_creds(file_inode(file_out)->i_sb);
@@ -603,6 +622,9 @@ static loff_t ovl_copyfile(struct file *file_in, loff_t pos_in,
 	fdput(real_in);
 	fdput(real_out);
 
+out_unlock:
+	inode_unlock(inode_out);
+
 	return ret;
 }
 

include/linux/fs.h

@@ -3104,7 +3104,7 @@ extern void __destroy_inode(struct inode *);
 extern struct inode *new_inode_pseudo(struct super_block *sb);
 extern struct inode *new_inode(struct super_block *sb);
 extern void free_inode_nonrcu(struct inode *inode);
-extern int should_remove_suid(struct dentry *);
+extern int setattr_should_drop_suidgid(struct user_namespace *, struct inode *);
 extern int file_remove_privs(struct file *);
 
 /*