[PATCH 6.1.y] ksmbd: use opener credentials for FSCTL mutations

[Sasha Levin <sashal@kernel.org>]

From: Namjae Jeon <linkinjeon@kernel.org>

[ Upstream commit c6394bcaf254c5baf9aff43376020be5db6d3316 ]

SET_SPARSE, SET_ZERO_DATA and SET_COMPRESSION operate on an open SMB
handle but call VFS xattr, fallocate or fileattr helpers with the current
ksmbd worker credentials. Those helpers can revalidate inode permissions,
ownership and LSM policy independently of the SMB handle access mask.

Run each operation with the credentials captured in the target file when
the handle was opened. Keep credential handling local to these single-file
FSCTLs rather than applying session credentials to the complete IOCTL
handler, which also contains handle-less and multi-handle operations.

Cc: stable@vger.kernel.org
Reported-by: Musaab Khan <musaab.khan@protonmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/server/smb2pdu.c |  3 +++
 fs/smb/server/vfs.c     | 20 +++++++++++++-------
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c
index 1d49439035d22f..f6fb391178b8c6 100644
--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -7716,6 +7716,7 @@ static inline int fsctl_set_sparse(struct ksmbd_work *work, u64 id,
 	if (fp->f_ci->m_fattr != old_fattr &&
 	    test_share_config_flag(work->tcon->share_conf,
 				   KSMBD_SHARE_FLAG_STORE_DOS_ATTRS)) {
+		const struct cred *saved_cred;
 		struct xattr_dos_attrib da;
 
 		ret = ksmbd_vfs_get_dos_attrib_xattr(user_ns,
@@ -7724,9 +7725,11 @@ static inline int fsctl_set_sparse(struct ksmbd_work *work, u64 id,
 			goto out;
 
 		da.attr = le32_to_cpu(fp->f_ci->m_fattr);
+		saved_cred = override_creds(fp->filp->f_cred);
 		ret = ksmbd_vfs_set_dos_attrib_xattr(user_ns,
 						     &fp->filp->f_path,
 						     &da, true);
+		revert_creds(saved_cred);
 		if (ret)
 			fp->f_ci->m_fattr = old_fattr;
 	}
diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 723f090458e7f8..1834dd4f255ec9 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -991,15 +991,21 @@ void ksmbd_vfs_set_fadvise(struct file *filp, __le32 option)
 int ksmbd_vfs_zero_data(struct ksmbd_work *work, struct ksmbd_file *fp,
 			loff_t off, loff_t len)
 {
+	const struct cred *saved_cred;
+	int err;
+
 	smb_break_all_levII_oplock(work, fp, 1);
+	saved_cred = override_creds(fp->filp->f_cred);
 	if (fp->f_ci->m_fattr & FILE_ATTRIBUTE_SPARSE_FILE_LE)
-		return vfs_fallocate(fp->filp,
-				     FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
-				     off, len);
-
-	return vfs_fallocate(fp->filp,
-			     FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE,
-			     off, len);
+		err = vfs_fallocate(fp->filp,
+				    FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+				    off, len);
+	else
+		err = vfs_fallocate(fp->filp,
+				    FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE,
+				    off, len);
+	revert_creds(saved_cred);
+	return err;
 }
 
 int ksmbd_vfs_fqar_lseek(struct ksmbd_file *fp, loff_t start, loff_t length,
-- 
2.53.0