[PATCH 6/6] mkfs: don't trample the gid set in the protofile

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

Catherine's recent changes to xfs/019 exposed a bug in how libxfs
handles setgid bits.  mkfs reads the desired gid in from the protofile,
but if the parent directory is setgid, it will override the user's
setting and (re)set the child's gid to the parent's gid.  Overriding
user settings is (probably) not the desired mode of operation, so create
a flag to struct cred to force the gid in the protofile.

It looks like this has been broken since ~2005.

Cc: Catherine Hoang <catherine.hoang@xxxxxxxxxx>
Fixes: 9f064b7e ("Provide mkfs options to easily exercise all inheritable attributes, esp. the extsize allocator hint. Merge of master-melb:xfs-cmds:24370a by kenmcd.")
Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Reviewed-by: Catherine Hoang <catherine.hoang@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
 include/xfs_inode.h |   11 +++++++----
 libxfs/util.c       |    3 ++-
 mkfs/proto.c        |    3 ++-
 3 files changed, 11 insertions(+), 6 deletions(-)


diff --git a/include/xfs_inode.h b/include/xfs_inode.h
index 08a62d83..db9faa57 100644
--- a/include/xfs_inode.h
+++ b/include/xfs_inode.h
@@ -164,10 +164,13 @@ static inline bool xfs_inode_has_bigtime(struct xfs_inode *ip)
 	return ip->i_diflags2 & XFS_DIFLAG2_BIGTIME;
 }
 
-typedef struct cred {
-	uid_t	cr_uid;
-	gid_t	cr_gid;
-} cred_t;
+/* Always set the child's GID to this value, even if the parent is setgid. */
+#define CRED_FORCE_GID	(1U << 0)
+struct cred {
+	uid_t		cr_uid;
+	gid_t		cr_gid;
+	unsigned int	cr_flags;
+};
 
 extern int	libxfs_dir_ialloc (struct xfs_trans **, struct xfs_inode *,
 				mode_t, nlink_t, xfs_dev_t, struct cred *,
diff --git a/libxfs/util.c b/libxfs/util.c
index 86deffae..ef01fcf8 100644
--- a/libxfs/util.c
+++ b/libxfs/util.c
@@ -271,7 +271,8 @@ libxfs_init_new_inode(
 	xfs_trans_ichgtime(tp, ip, XFS_ICHGTIME_CHG | XFS_ICHGTIME_MOD);
 
 	if (pip && (VFS_I(pip)->i_mode & S_ISGID)) {
-		VFS_I(ip)->i_gid = VFS_I(pip)->i_gid;
+		if (!(cr->cr_flags & CRED_FORCE_GID))
+			VFS_I(ip)->i_gid = VFS_I(pip)->i_gid;
 		if ((VFS_I(pip)->i_mode & S_ISGID) && (mode & S_IFMT) == S_IFDIR)
 			VFS_I(ip)->i_mode |= S_ISGID;
 	}
diff --git a/mkfs/proto.c b/mkfs/proto.c
index ef130ed6..127d87dd 100644
--- a/mkfs/proto.c
+++ b/mkfs/proto.c
@@ -378,7 +378,7 @@ parseproto(
 	xfs_trans_t	*tp;
 	int		val;
 	int		isroot = 0;
-	cred_t		creds;
+	struct cred	creds;
 	char		*value;
 	struct xfs_name	xname;
 
@@ -446,6 +446,7 @@ parseproto(
 	mode |= val;
 	creds.cr_uid = (int)getnum(getstr(pp), 0, 0, false);
 	creds.cr_gid = (int)getnum(getstr(pp), 0, 0, false);
+	creds.cr_flags = CRED_FORCE_GID;
 	xname.name = (unsigned char *)name;
 	xname.len = name ? strlen(name) : 0;
 	xname.type = 0;