On Wed, Sep 21, 2011 at 7:43 AM, Jeff Layton <jlayton@xxxxxxxxx> wrote:
> On Wed, 21 Sep 2011 07:35:06 -0500
> Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx> wrote:
>
>> On Wed, Sep 21, 2011 at 6:43 AM, Jeff Layton <jlayton@xxxxxxxxx> wrote:
>> > On Tue, 20 Sep 2011 13:26:50 -0500
>> > shirishpargaonkar@xxxxxxxxx wrote:
>> >
>> >> From: Shirish Pargaonkar <shirishpargaonkar@xxxxxxxxx>
>> >>
>> >>
>> >> 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.
>> >>
>> >> These mount options are mutually excluisve to mount option mulituser.
>> >>
>> >> 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@xxxxxxxxx>
>> >> ---
>> >> fs/cifs/cifs_fs_sb.h | 3 +++
>> >> fs/cifs/cifsacl.c | 23 ++++++++++++++++++-----
>> >> fs/cifs/cifsglob.h | 6 +++++-
>> >> fs/cifs/connect.c | 14 ++++++++++++++
>> >> fs/cifs/dir.c | 22 +++++++++++++++++++---
>> >> fs/cifs/file.c | 24 ++++++++++++++++++++++--
>> >> fs/cifs/link.c | 23 ++++++++++++++++++-----
>> >> 7 files changed, 99 insertions(+), 16 deletions(-)
>> >>
>> >> diff --git a/fs/cifs/cifs_fs_sb.h b/fs/cifs/cifs_fs_sb.h
>> >> index 7260e11..f5483c8 100644
>> >> --- a/fs/cifs/cifs_fs_sb.h
>> >> +++ b/fs/cifs/cifs_fs_sb.h
>> >> @@ -43,6 +43,7 @@
>> >> #define CIFS_MOUNT_STRICT_IO 0x40000 /* strict cache mode */
>> >> #define CIFS_MOUNT_RWPIDFORWARD 0x80000 /* use pid forwarding for rw */
>> >> #define CIFS_MOUNT_POSIXACL 0x100000 /* mirror of MS_POSIXACL in mnt_cifs_flags */
>> >> +#define CIFS_MOUNT_CIFS_BACKUP 0x200000 /* open file with backup intent bit */
>> >>
>> >> struct cifs_sb_info {
>> >> struct rb_root tlink_tree;
>> >> @@ -55,6 +56,8 @@ struct cifs_sb_info {
>> >> atomic_t active;
>> >> uid_t mnt_uid;
>> >> gid_t mnt_gid;
>> >> + uid_t mnt_backupuid;
>> >> + gid_t mnt_backupgid;
>> >> mode_t mnt_file_mode;
>> >> mode_t mnt_dir_mode;
>> >> unsigned int mnt_cifs_flags;
>> >> diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
>> >> index d0f59fa..a0af87a 100644
>> >> --- a/fs/cifs/cifsacl.c
>> >> +++ b/fs/cifs/cifsacl.c
>> >> @@ -945,7 +945,7 @@ static struct cifs_ntsd *get_cifs_acl_by_path(struct cifs_sb_info *cifs_sb,
>> >> {
>> >> struct cifs_ntsd *pntsd = NULL;
>> >> int oplock = 0;
>> >> - int xid, rc;
>> >> + int xid, rc, create_options = 0;
>> >> __u16 fid;
>> >> struct cifs_tcon *tcon;
>> >> struct tcon_link *tlink = cifs_sb_tlink(cifs_sb);
>> >> @@ -956,9 +956,18 @@ static struct cifs_ntsd *get_cifs_acl_by_path(struct cifs_sb_info *cifs_sb,
>> >> tcon = tlink_tcon(tlink);
>> >> xid = GetXid();
>> >>
>> >> - rc = CIFSSMBOpen(xid, tcon, path, FILE_OPEN, READ_CONTROL, 0,
>> >> - &fid, &oplock, NULL, cifs_sb->local_nls,
>> >> - cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >> + }
>> >> +
>> > ^^^^^^^^^^^^^^
>> > Ugh, please put the ugliness above in a helper
>> > function. Maybe something like:
>> >
>> > if (backup_cred(cifs_sb))
>> > create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >
>> > Also, why is this dependent on CIFS_MOUNT_CIFS_ACL?
>> >
>> >> + rc = CIFSSMBOpen(xid, tcon, path, FILE_OPEN, READ_CONTROL,
>> >> + create_options, &fid, &oplock, NULL, cifs_sb->local_nls,
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);
>> >> if (!rc) {
>> >> rc = CIFSSMBGetCIFSACL(xid, tcon, fid, &pntsd, pacllen);
>> >> CIFSSMBClose(xid, tcon, fid);
>> >> @@ -995,7 +1004,7 @@ static int set_cifs_acl_by_path(struct cifs_sb_info *cifs_sb, const char *path,
>> >> struct cifs_ntsd *pnntsd, u32 acllen)
>> >> {
>> >> int oplock = 0;
>> >> - int xid, rc;
>> >> + int xid, rc, create_options = 0;
>> >> __u16 fid;
>> >> struct cifs_tcon *tcon;
>> >> struct tcon_link *tlink = cifs_sb_tlink(cifs_sb);
>> >> @@ -1006,6 +1015,10 @@ static int set_cifs_acl_by_path(struct cifs_sb_info *cifs_sb, const char *path,
>> >> tcon = tlink_tcon(tlink);
>> >> xid = GetXid();
>> >>
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP)
>> >> + create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >> +
>> > ^^^^^^^^^^^^
>> > Why aren't you checking the user/group here?
>> >
>> >> rc = CIFSSMBOpen(xid, tcon, path, FILE_OPEN, WRITE_DAC, 0,
>> >> &fid, &oplock, NULL, cifs_sb->local_nls,
>> >> cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);
>> >> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
>> >> index 95dad9d..cd0d7fa 100644
>> >> --- a/fs/cifs/cifsglob.h
>> >> +++ b/fs/cifs/cifsglob.h
>> >> @@ -167,6 +167,8 @@ struct smb_vol {
>> >> uid_t cred_uid;
>> >> uid_t linux_uid;
>> >> gid_t linux_gid;
>> >> + uid_t backupuid;
>> >> + gid_t backupgid;
>> >> mode_t file_mode;
>> >> mode_t dir_mode;
>> >> unsigned secFlg;
>> >> @@ -179,6 +181,7 @@ struct smb_vol {
>> >> bool noperm:1;
>> >> bool no_psx_acl:1; /* set if posix acl support should be disabled */
>> >> bool cifs_acl:1;
>> >> + bool cifs_backup:1; /* to indicates backup intent during file open */
>> >> bool no_xattr:1; /* set if xattr (EA) support should be disabled*/
>> >> bool server_ino:1; /* use inode numbers from server ie UniqueId */
>> >> bool direct_io:1;
>> >> @@ -219,7 +222,8 @@ struct smb_vol {
>> >> CIFS_MOUNT_OVERR_GID | CIFS_MOUNT_DYNPERM | \
>> >> CIFS_MOUNT_NOPOSIXBRL | CIFS_MOUNT_NOSSYNC | \
>> >> CIFS_MOUNT_FSCACHE | CIFS_MOUNT_MF_SYMLINKS | \
>> >> - CIFS_MOUNT_MULTIUSER | CIFS_MOUNT_STRICT_IO)
>> >> + CIFS_MOUNT_MULTIUSER | CIFS_MOUNT_STRICT_IO | \
>> >> + CIFS_MOUNT_CIFS_BACKUP)
>> >>
>> >> #define CIFS_MS_MASK (MS_RDONLY | MS_MANDLOCK | MS_NOEXEC | MS_NOSUID | \
>> >> MS_NODEV | MS_SYNCHRONOUS)
>> >> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
>> >> index f4af4cc..a56624a 100644
>> >> --- a/fs/cifs/connect.c
>> >> +++ b/fs/cifs/connect.c
>> >> @@ -854,6 +854,8 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
>> >> vol->cred_uid = current_uid();
>> >> vol->linux_uid = current_uid();
>> >> vol->linux_gid = current_gid();
>> >> + vol->backupuid = NO_CHANGE_32;
>> >> + vol->backupgid = NO_CHANGE_32;
>> >>
>> >> /* default to only allowing write access to owner of the mount */
>> >> vol->dir_mode = vol->file_mode = S_IRUGO | S_IXUGO | S_IWUSR;
>> >> @@ -883,6 +885,7 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
>> >> cFYI(1, "Null separator not allowed");
>> >> }
>> >> }
>> >> + vol->cifs_backup = 0; /* no backup intent */
>> >>
>> >> while ((data = strsep(&options, separator)) != NULL) {
>> >> if (!*data)
>> >> @@ -1405,6 +1408,8 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
>> >> vol->rwpidforward = 1;
>> >> } else if (strnicmp(data, "cifsacl", 7) == 0) {
>> >> vol->cifs_acl = 1;
>> >> + } else if (strnicmp(data, "backup", 7) == 0) {
>> >> + vol->cifs_backup = 1;
>> >> } else if (strnicmp(data, "nocifsacl", 9) == 0) {
>> >> vol->cifs_acl = 0;
>> >> } else if (strnicmp(data, "acl", 3) == 0) {
>> >> @@ -1442,6 +1447,10 @@ cifs_parse_mount_options(const char *mountdata, const char *devname,
>> >> vol->mfsymlinks = true;
>> >> } else if (strnicmp(data, "multiuser", 8) == 0) {
>> >> vol->multiuser = true;
>> >> + } else if (!strnicmp(data, "backupuid", 9) && value && *value) {
>> >> + kstrtouint(value, 0, &vol->backupuid);
>> >> + } else if (!strnicmp(data, "backupgid", 9) && value && *value) {
>> >> + kstrtouint(value, 0, &vol->backupgid);
>> >> } else
>> >> printk(KERN_WARNING "CIFS: Unknown mount option %s\n",
>> >> data);
>> >> @@ -2733,6 +2742,8 @@ void cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
>> >>
>> >> cifs_sb->mnt_uid = pvolume_info->linux_uid;
>> >> cifs_sb->mnt_gid = pvolume_info->linux_gid;
>> >> + cifs_sb->mnt_backupuid = pvolume_info->backupuid;
>> >> + cifs_sb->mnt_backupgid = pvolume_info->backupgid;
>> >> cifs_sb->mnt_file_mode = pvolume_info->file_mode;
>> >> cifs_sb->mnt_dir_mode = pvolume_info->dir_mode;
>> >> cFYI(1, "file mode: 0x%x dir mode: 0x%x",
>> >> @@ -2763,6 +2774,9 @@ void cifs_setup_cifs_sb(struct smb_vol *pvolume_info,
>> >> cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_RWPIDFORWARD;
>> >> if (pvolume_info->cifs_acl)
>> >> cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_CIFS_ACL;
>> >> + if (pvolume_info->backupuid != NO_CHANGE_32 ||
>> >> + pvolume_info->backupgid != NO_CHANGE_32)
>> >> + cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_CIFS_BACKUP;
>> >> if (pvolume_info->override_uid)
>> >> cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_OVERR_UID;
>> >> if (pvolume_info->override_gid)
>> >> diff --git a/fs/cifs/dir.c b/fs/cifs/dir.c
>> >> index 72d448b..8a2bff6 100644
>> >> --- a/fs/cifs/dir.c
>> >> +++ b/fs/cifs/dir.c
>> >> @@ -243,7 +243,14 @@ cifs_create(struct inode *inode, struct dentry *direntry, int mode,
>> >> */
>> >> if (!tcon->unix_ext && (mode & S_IWUGO) == 0)
>> >> create_options |= CREATE_OPTION_READONLY;
>> >> -
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >> + }
>> >> if (tcon->ses->capabilities & CAP_NT_SMBS)
>> >> rc = CIFSSMBOpen(xid, tcon, full_path, disposition,
>> >> desiredAccess, create_options,
>> >> @@ -357,6 +364,7 @@ int cifs_mknod(struct inode *inode, struct dentry *direntry, int mode,
>> >> {
>> >> int rc = -EPERM;
>> >> int xid;
>> >> + int create_options = CREATE_NOT_DIR | CREATE_OPTION_SPECIAL;
>> >> struct cifs_sb_info *cifs_sb;
>> >> struct tcon_link *tlink;
>> >> struct cifs_tcon *pTcon;
>> >> @@ -431,9 +439,17 @@ int cifs_mknod(struct inode *inode, struct dentry *direntry, int mode,
>> >> return rc;
>> >> }
>> >>
>> >> - /* FIXME: would WRITE_OWNER | WRITE_DAC be better? */
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >> + }
>> >> +
>> >> rc = CIFSSMBOpen(xid, pTcon, full_path, FILE_CREATE,
>> >> - GENERIC_WRITE, CREATE_NOT_DIR | CREATE_OPTION_SPECIAL,
>> >> + GENERIC_WRITE, create_options,
>> >> &fileHandle, &oplock, buf, cifs_sb->local_nls,
>> >> cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR);
>> >> if (rc)
>> >> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
>> >> index 9f41a10..12eed36 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 +211,18 @@ cifs_nt_open(char *full_path, struct inode *inode, struct cifs_sb_info *cifs_sb,
>> >> if (!buf)
>> >> return -ENOMEM;
>> >>
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + 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 +475,7 @@ 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 +535,15 @@ static int cifs_reopen_file(struct cifsFileInfo *pCifsFile, bool can_flush)
>> >>
>> >> desiredAccess = cifs_convert_flags(pCifsFile->f_flags);
>> >>
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + 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 +551,7 @@ 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) {
>> >> diff --git a/fs/cifs/link.c b/fs/cifs/link.c
>> >> index db3f18c..81b6bf9 100644
>> >> --- a/fs/cifs/link.c
>> >> +++ b/fs/cifs/link.c
>> >> @@ -183,14 +183,20 @@ CIFSFormatMFSymlink(u8 *buf, unsigned int buf_len, const char *link_str)
>> >> static int
>> >> CIFSCreateMFSymLink(const int xid, struct cifs_tcon *tcon,
>> >> const char *fromName, const char *toName,
>> >> - const struct nls_table *nls_codepage, int remap)
>> >> + struct cifs_sb_info *cifs_sb)
>> >> {
>> >> int rc;
>> >> int oplock = 0;
>> >> + int remap;
>> >> + int create_options = CREATE_NOT_DIR;
>> >> __u16 netfid = 0;
>> >> u8 *buf;
>> >> unsigned int bytes_written = 0;
>> >> struct cifs_io_parms io_parms;
>> >> + struct nls_table *nls_codepage;
>> >> +
>> >> + nls_codepage = cifs_sb->local_nls;
>> >> + remap = cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MAP_SPECIAL_CHR;
>> >>
>> >> buf = kmalloc(CIFS_MF_SYMLINK_FILE_SIZE, GFP_KERNEL);
>> >> if (!buf)
>> >> @@ -202,8 +208,17 @@ CIFSCreateMFSymLink(const int xid, struct cifs_tcon *tcon,
>> >> return rc;
>> >> }
>> >>
>> >> + if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_ACL &&
>> >> + cifs_sb->mnt_cifs_flags & CIFS_MOUNT_CIFS_BACKUP) {
>> >> + if ((cifs_sb->mnt_backupuid != NO_CHANGE_32 &&
>> >> + cifs_sb->mnt_backupuid == current_euid()) ||
>> >> + (cifs_sb->mnt_backupgid != NO_CHANGE_32 &&
>> >> + in_group_p(cifs_sb->mnt_backupgid)))
>> >> + create_options |= CREATE_OPEN_BACKUP_INTENT;
>> >> + }
>> >> +
>> >> rc = CIFSSMBOpen(xid, tcon, fromName, FILE_CREATE, GENERIC_WRITE,
>> >> - CREATE_NOT_DIR, &netfid, &oplock, NULL,
>> >> + create_options, &netfid, &oplock, NULL,
>> >> nls_codepage, remap);
>> >> if (rc != 0) {
>> >> kfree(buf);
>> >> @@ -559,9 +574,7 @@ cifs_symlink(struct inode *inode, struct dentry *direntry, const char *symname)
>> >> /* BB what if DFS and this volume is on different share? BB */
>> >> if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS)
>> >> rc = CIFSCreateMFSymLink(xid, pTcon, full_path, symname,
>> >> - cifs_sb->local_nls,
>> >> - cifs_sb->mnt_cifs_flags &
>> >> - CIFS_MOUNT_MAP_SPECIAL_CHR);
>> >> + cifs_sb);
>> >> else if (pTcon->unix_ext)
>> >> rc = CIFSUnixCreateSymLink(xid, pTcon, full_path, symname,
>> >> cifs_sb->local_nls);
>> >
>> >
>> > --
>> > Jeff Layton <jlayton@xxxxxxxxx>
>> >
>>
>> Jeff, Thanks. Will correct these. We probably should
>> check in kernel that the options multiuser and either or
>> both of backupuid and backupgid are not specified
>> at the same time besides checking them in mount.cifs.
>>
>
> Why? I see no reason why this must be mutually exclusive with multiuser.
>
I think you are right. With cifs client restricting usage of this backup id
option to either to a specified uid or gid, it does not matter what the
uid/gid associated with the subsequent spawned sessions are.
Regarding CIFS_ACL, since this particular right is mostly/prominently
utilized against Windows servers, the backup intent (and hence mount
options backupuid/backupgid) was deemed being used in conjunction
with mount option cifsacl.
Regards,
Shirish
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