[PATCH v2 3/5] powerpc/spufs: check permissions in spufs_setattr()

[Junrui Luo via B4 Relay <devnull+moonafterrain.outlook.com@kernel.org>]

From: Junrui Luo <moonafterrain@outlook.com>

spufs_setattr() applies the caller's attributes with setattr_copy() but
never calls setattr_prepare(). notify_change() leaves that to the
filesystem: it runs only may_setattr(), while inode_owner_or_capable()
and the CAP_CHOWN test live inside setattr_prepare(). setattr_copy()
performs no checking of its own.

The handler is installed for every regular spufs file, so mode and
ownership of another user's context files can be changed without the
usual authorization.

Call setattr_prepare() before setattr_copy(). The existing ATTR_SIZE
test stays ahead of it so that resizing a spufs file keeps returning
-EINVAL. &nop_mnt_idmap matches the adjacent setattr_copy() call.

Fixes: 67207b9664a8 ("[PATCH] spufs: The SPU file system, base")
Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Assisted-by: Claude:claude-opus-5
Cc: stable@vger.kernel.org
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
---
 arch/powerpc/platforms/cell/spufs/inode.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/platforms/cell/spufs/inode.c b/arch/powerpc/platforms/cell/spufs/inode.c
index 2b54afb31529..c2b15c30f7c0 100644
--- a/arch/powerpc/platforms/cell/spufs/inode.c
+++ b/arch/powerpc/platforms/cell/spufs/inode.c
@@ -96,10 +96,14 @@ spufs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
 	      struct iattr *attr)
 {
 	struct inode *inode = d_inode(dentry);
+	int ret;
 
 	if ((attr->ia_valid & ATTR_SIZE) &&
 	    (attr->ia_size != inode->i_size))
 		return -EINVAL;
+	ret = setattr_prepare(&nop_mnt_idmap, dentry, attr);
+	if (ret)
+		return ret;
 	setattr_copy(&nop_mnt_idmap, inode, attr);
 	mark_inode_dirty(inode);
 	return 0;

-- 
2.51.2