[PATCH v2 1/2] cifs: Add fallback for SMB2 CREATE without FILE_READ_ATTRIBUTES

[Pali Rohár]

Some operations, like WRITE, does not require FILE_READ_ATTRIBUTES access.

So when FILE_READ_ATTRIBUTES is not explicitly requested for
smb2_open_file() then first try to do SMB2 CREATE with FILE_READ_ATTRIBUTES
access (like it was before) and then fallback to SMB2 CREATE without
FILE_READ_ATTRIBUTES access (less common case).

This change allows to complete WRITE operation to a file when it does not
grant FILE_READ_ATTRIBUTES permission and its parent directory does not
grant READ_DATA permission (parent directory READ_DATA is implicit grant of
child FILE_READ_ATTRIBUTES permission).

Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
---
 fs/smb/client/smb2file.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/smb2file.c b/fs/smb/client/smb2file.c
index e4ae8d2d5bd0..ff255fdc4532 100644
--- a/fs/smb/client/smb2file.c
+++ b/fs/smb/client/smb2file.c
@@ -152,16 +152,25 @@ int smb2_open_file(const unsigned int xid, struct cifs_open_parms *oparms, __u32
 	int err_buftype = CIFS_NO_BUFFER;
 	struct cifs_fid *fid = oparms->fid;
 	struct network_resiliency_req nr_ioctl_req;
+	bool retry_without_read_attributes = false;
 
 	smb2_path = cifs_convert_path_to_utf16(oparms->path, oparms->cifs_sb);
 	if (smb2_path == NULL)
 		return -ENOMEM;
 
-	oparms->desired_access |= FILE_READ_ATTRIBUTES;
+	if (!(oparms->desired_access & FILE_READ_ATTRIBUTES)) {
+		oparms->desired_access |= FILE_READ_ATTRIBUTES;
+		retry_without_read_attributes = true;
+	}
 	smb2_oplock = SMB2_OPLOCK_LEVEL_BATCH;
 
 	rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL, &err_iov,
 		       &err_buftype);
+	if (rc == -EACCES && retry_without_read_attributes) {
+		oparms->desired_access &= ~FILE_READ_ATTRIBUTES;
+		rc = SMB2_open(xid, oparms, smb2_path, &smb2_oplock, smb2_data, NULL, &err_iov,
+			       &err_buftype);
+	}
 	if (rc && data) {
 		struct smb2_hdr *hdr = err_iov.iov_base;
 
-- 
2.20.1