[SRU Hirsute] xfs: fix up non-directory creation in SGID directories

[Thadeu Lima de Souza Cascardo]

From: Christoph Hellwig <hch at lst.de>

BugLink: https://bugs.launchpad.net/bugs/1950239

XFS always inherits the SGID bit if it is set on the parent inode, while
the generic inode_init_owner does not do this in a few cases where it can
create a possible security problem, see commit 0fa3ecd87848
("Fix up non-directory creation in SGID directories") for details.

Switch XFS to use the generic helper for the normal path to fix this,
just keeping the simple field inheritance open coded for the case of the
non-sgid case with the bsdgrpid mount option.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Christian Brauner <christian.brauner at ubuntu.com>
Signed-off-by: Christoph Hellwig <hch at lst.de>
Reviewed-by: Darrick J. Wong <djwong at kernel.org>
Signed-off-by: Darrick J. Wong <djwong at kernel.org>
(cherry picked from commit 01ea173e103edd5ec41acec65b9261b87e123fc2)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 fs/xfs/xfs_inode.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index b7352bc4c815..7289325aa5c7 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -775,6 +775,7 @@ xfs_init_new_inode(
 	prid_t			prid,
 	struct xfs_inode	**ipp)
 {
+	struct inode		*dir = pip ? VFS_I(pip) : NULL;
 	struct xfs_mount	*mp = tp->t_mountp;
 	struct xfs_inode	*ip;
 	unsigned int		flags;
@@ -804,18 +805,17 @@ xfs_init_new_inode(
 
 	ASSERT(ip != NULL);
 	inode = VFS_I(ip);
-	inode->i_mode = mode;
 	set_nlink(inode, nlink);
-	inode->i_uid = current_fsuid();
 	inode->i_rdev = rdev;
 	ip->i_d.di_projid = prid;
 
-	if (pip && XFS_INHERIT_GID(pip)) {
-		inode->i_gid = VFS_I(pip)->i_gid;
-		if ((VFS_I(pip)->i_mode & S_ISGID) && S_ISDIR(mode))
-			inode->i_mode |= S_ISGID;
+	if (dir && !(dir->i_mode & S_ISGID) &&
+	    (mp->m_flags & XFS_MOUNT_GRPID)) {
+		inode->i_uid = current_fsuid();
+		inode->i_gid = dir->i_gid;
+		inode->i_mode = mode;
 	} else {
-		inode->i_gid = current_fsgid();
+		inode_init_owner(inode, dir, mode);
 	}
 
 	/*
-- 
2.32.0