cifs: Add mount options for backup intent (try #6)

Add mount options backupuid and backugid.

It allows an authenticated user to access files with the intent to back them
up including their ACLs, who may not have access permission but has
"Backup files and directories user right" on them (by virtue of being part
of the built-in group Backup Operators.

When mount options backupuid is specified, cifs client restricts the
use of backup intents to the user whose effective user id is specified
along with the mount option.

When mount options backupgid is specified, cifs client restricts the
use of backup intents to the users whose effective user id belongs to the
group id specified along with the mount option.

If an authenticated user is not part of the built-in group Backup Operators
at the server, access to such files is denied, even if allowed by the client.

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 8e184150cfb5..237192ae7587 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -174,6 +174,7 @@ cifs_nt_open(char *full_path, struct inode *inode, struct cifs_sb_info *cifs_sb,
         int rc;
         int desiredAccess;
         int disposition;
+        int create_options = CREATE_NOT_DIR;
         FILE_ALL_INFO *buf;
 
         desiredAccess = cifs_convert_flags(f_flags);
@@ -210,9 +211,12 @@ cifs_nt_open(char *full_path, struct inode *inode, struct cifs_sb_info *cifs_sb,
         if (!buf)
                 return -ENOMEM;
 
+        if (backup_cred(cifs_sb))
+                create_options |= CREATE_OPEN_BACKUP_INTENT;
+
         if (tcon->ses->capabilities & CAP_NT_SMBS)
                 rc = CIFSSMBOpen(xid, tcon, full_path, disposition,
-                         desiredAccess, CREATE_NOT_DIR, pnetfid, poplock, buf,
+                         desiredAccess, create_options, pnetfid, poplock, buf,
                          cifs_sb->local_nls, cifs_sb->mnt_cifs_flags
                                  & CIFS_MOUNT_MAP_SPECIAL_CHR);
         else
@@ -465,6 +469,7 @@ static int cifs_reopen_file(struct cifsFileInfo *pCifsFile, bool can_flush)
         char *full_path = NULL;
         int desiredAccess;
         int disposition = FILE_OPEN;
+        int create_options = CREATE_NOT_DIR;
         __u16 netfid;
 
         xid = GetXid();
@@ -524,6 +529,9 @@ static int cifs_reopen_file(struct cifsFileInfo *pCifsFile, bool can_flush)
 
         desiredAccess = cifs_convert_flags(pCifsFile->f_flags);
 
+        if (backup_cred(cifs_sb))
+                create_options |= CREATE_OPEN_BACKUP_INTENT;
+
         /* Can not refresh inode by passing in file_info buf to be returned
            by SMBOpen and then calling get_inode_info with returned buf
            since file might have write behind data that needs to be flushed
@@ -531,7 +539,7 @@ static int cifs_reopen_file(struct cifsFileInfo *pCifsFile, bool can_flush)
            that inode was not dirty locally we could do this */
 
         rc = CIFSSMBOpen(xid, tcon, full_path, disposition, desiredAccess,
-                         CREATE_NOT_DIR, &netfid, &oplock, NULL,
+                         create_options, &netfid, &oplock, NULL,
                          cifs_sb->local_nls, cifs_sb->mnt_cifs_flags &
                                 CIFS_MOUNT_MAP_SPECIAL_CHR);
         if (rc) {