Re: [PATCH 6/7] cifs: Fix creating of SFU fifo and socket special files

From: Steve French
Date: Fri Sep 13 2024 - 18:33:45 EST

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One other thing which worried me a bit is that I confirmed that an
empty file with the system attribute set was matched as a FIFO file
type (when you mount with "sfu") - this seems risky.

On Fri, Sep 13, 2024 at 5:14 PM Steve French <smfrench@xxxxxxxxx> wrote:
>
> How did you find the format of the FIFO and SOCK file types? I
> couldn't find any references to those so added two new types to allow
> current Linux to be able to create these (especially since they are
> opaque to the server and thus low risk).
>
> > + case S_IFSOCK:
> > - strscpy(pdev.type, "LnxSOCK");
> > + /* SFU socket is system file with one zero byte */
> > + pdev_len = 1;
> > + pdev.type[0] = '\0';
> > break;
> > case S_IFIFO:
> > - strscpy(pdev.type, "LnxFIFO");
> > + /* SFU fifo is system file which is empty */
> > + pdev_len = 0;
>
> My worry about the suggested change above is that it is possible that
> we could accidentally match to an empty file. We intentionally added
> the two new dev.type fields for these to avoid collisions with other
> things (and since they are Linux specific). It seems risky to have an
> empty file with the system attribute marked as a FIFO, and similarly a
> file with one byte null as Socket. Since this is for only the Linux
> client to recognize, I wanted to do something safe for those file
> types less likely to be confusing (ie strings for Socket and FIFO that
> were similar in length and format to the other special files seemed
> intuitive) and "LnxFIFO" and LnxSOCK" were used as the tags in the
> file to reduce confusion ie the tags for those two start with "Lnx" -
> ie "something used for Linux client" not related to the original
> Interix (those begin with "Intx").
>
> Note that in the long run we hope to use reparse points by default in
> more servers to store special files like this but there are a few
> cases for unusual workloads that need special file support that would
> have to use sfu still. The newer reparse tags that Windows uses "WSL"
> have the advantage that they require fewer roundtrips to query (since
> the file type is in the reparse tag).
>
> Also noticed an interesting problem when mounted with "sfu" -
> "smbgetinfo filebasicinfo /mnt/fifo1" will hang (in sys_open). Is
> that expected for a FIFO?
>
> On Fri, Sep 13, 2024 at 3:07 PM Pali Rohár <pali@xxxxxxxxxx> wrote:
> >
> > On Thursday 12 September 2024 14:05:47 Pali Rohár wrote:
> > > SFU-style fifo is empty file with system attribute set. This format is used
> > > by old Microsoft POSIX subsystem and later also by OpenNT/Interix subsystem
> > > (which replaced Microsoft POSIX subsystem and is part of Microsoft SFU).
> > >
> > > SFU-style socket is file which has system attribute set and file content is
> > > one zero byte. This format was introduced in Interix 3.0 subsystem, as part
> > > of the Microsoft SFU 3.0 and is used also by all later versions. Previous
> > > versions had no UNIX domain socket support.
> > >
> > > Currently when sfu mount option is specified then CIFS creates fifo and
> > > socket special files with some strange LnxSOCK or LnxFIFO content which is
> > > not compatible with Microsoft SFU and neither recognized by other SMB
> > > implementations which have some SFU support, including older Linux cifs
> > > implementations.
> > >
> > > So when sfu mount option is specified, create all fifo and socket special
> > > files compatible with SFU format to achieve SFU interop, as it is expected
> > > by sfu mount option.
> > >
> > > Signed-off-by: Pali Rohár <pali@xxxxxxxxxx>
> >
> > Fixes: 72bc63f5e23a ("smb3: fix creating FIFOs when mounting with "sfu" mount option")
> > Fixes: 518549c120e6 ("cifs: fix creating sockets when using sfu mount options")
> >
> > I located commits which introduced those strange LnxSOCK or LnxFIFO
> > types which are not compatible with SFU. I would suggest to add those
> > two Fixes: tags into commit message for reference.
> >
> > > ---
> > > fs/smb/client/cifssmb.c | 8 ++++----
> > > fs/smb/client/smb1ops.c | 2 +-
> > > fs/smb/client/smb2ops.c | 29 +++++++++++++++++++----------
> > > 3 files changed, 24 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
> > > index cfae2e918209..0ffc45aa5e2c 100644
> > > --- a/fs/smb/client/cifssmb.c
> > > +++ b/fs/smb/client/cifssmb.c
> > > @@ -1076,8 +1076,8 @@ SMBLegacyOpen(const unsigned int xid, struct cifs_tcon *tcon,
> > > pSMB->OpenFlags |= cpu_to_le16(REQ_MORE_INFO);
> > > pSMB->Mode = cpu_to_le16(access_flags_to_smbopen_mode(access_flags));
> > > pSMB->Mode |= cpu_to_le16(0x40); /* deny none */
> > > - /* set file as system file if special file such
> > > - as fifo and server expecting SFU style and
> > > + /* set file as system file if special file such as fifo,
> > > + * socket, char or block and server expecting SFU style and
> > > no Unix extensions */
> > >
> > > if (create_options & CREATE_OPTION_SPECIAL)
> > > @@ -1193,8 +1193,8 @@ CIFS_open(const unsigned int xid, struct cifs_open_parms *oparms, int *oplock,
> > > req->AllocationSize = 0;
> > >
> > > /*
> > > - * Set file as system file if special file such as fifo and server
> > > - * expecting SFU style and no Unix extensions.
> > > + * Set file as system file if special file such as fifo, socket, char
> > > + * or block and server expecting SFU style and no Unix extensions.
> > > */
> > > if (create_options & CREATE_OPTION_SPECIAL)
> > > req->FileAttributes = cpu_to_le32(ATTR_SYSTEM);
> > > diff --git a/fs/smb/client/smb1ops.c b/fs/smb/client/smb1ops.c
> > > index e1f2feb56f45..e03c91a49650 100644
> > > --- a/fs/smb/client/smb1ops.c
> > > +++ b/fs/smb/client/smb1ops.c
> > > @@ -1078,7 +1078,7 @@ cifs_make_node(unsigned int xid, struct inode *inode,
> > > /*
> > > * Check if mounted with mount parm 'sfu' mount parm.
> > > * SFU emulation should work with all servers, but only
> > > - * supports block and char device (no socket & fifo),
> > > + * supports block and char device, socket & fifo,
> > > * and was used by default in earlier versions of Windows
> > > */
> > > if (!(cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL))
> > > diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
> > > index 9c2d065d3cc4..9e90672caf60 100644
> > > --- a/fs/smb/client/smb2ops.c
> > > +++ b/fs/smb/client/smb2ops.c
> > > @@ -5066,26 +5066,32 @@ static int __cifs_sfu_make_node(unsigned int xid, struct inode *inode,
> > > struct cifs_fid fid;
> > > unsigned int bytes_written;
> > > struct win_dev pdev = {};
> > > + size_t pdev_len = 0;
> > > struct kvec iov[2];
> > > __u32 oplock = server->oplocks ? REQ_OPLOCK : 0;
> > > int rc;
> > >
> > > switch (mode & S_IFMT) {
> > > case S_IFCHR:
> > > + pdev_len = sizeof(pdev);
> > > memcpy(pdev.type, "IntxCHR\0", 8);
> > > pdev.major = cpu_to_le64(MAJOR(dev));
> > > pdev.minor = cpu_to_le64(MINOR(dev));
> > > break;
> > > case S_IFBLK:
> > > + pdev_len = sizeof(pdev);
> > > memcpy(pdev.type, "IntxBLK\0", 8);
> > > pdev.major = cpu_to_le64(MAJOR(dev));
> > > pdev.minor = cpu_to_le64(MINOR(dev));
> > > break;
> > > case S_IFSOCK:
> > > - strscpy(pdev.type, "LnxSOCK");
> > > + /* SFU socket is system file with one zero byte */
> > > + pdev_len = 1;
> > > + pdev.type[0] = '\0';
> > > break;
> > > case S_IFIFO:
> > > - strscpy(pdev.type, "LnxFIFO");
> > > + /* SFU fifo is system file which is empty */
> > > + pdev_len = 0;
> > > break;
> > > default:
> > > return -EPERM;
> > > @@ -5100,14 +5106,17 @@ static int __cifs_sfu_make_node(unsigned int xid, struct inode *inode,
> > > if (rc)
> > > return rc;
> > >
> > > - io_parms.pid = current->tgid;
> > > - io_parms.tcon = tcon;
> > > - io_parms.length = sizeof(pdev);
> > > - iov[1].iov_base = &pdev;
> > > - iov[1].iov_len = sizeof(pdev);
> > > + if (pdev_len > 0) {
> > > + io_parms.pid = current->tgid;
> > > + io_parms.tcon = tcon;
> > > + io_parms.length = pdev_len;
> > > + iov[1].iov_base = &pdev;
> > > + iov[1].iov_len = pdev_len;
> > > +
> > > + rc = server->ops->sync_write(xid, &fid, &io_parms,
> > > + &bytes_written, iov, 1);
> > > + }
> > >
> > > - rc = server->ops->sync_write(xid, &fid, &io_parms,
> > > - &bytes_written, iov, 1);
> > > server->ops->close(xid, tcon, &fid);
> > > return rc;
> > > }
> > > @@ -5149,7 +5158,7 @@ static int smb2_make_node(unsigned int xid, struct inode *inode,
> > > /*
> > > * Check if mounted with mount parm 'sfu' mount parm.
> > > * SFU emulation should work with all servers, but only
> > > - * supports block and char device (no socket & fifo),
> > > + * supports block and char device, socket & fifo,
> > > * and was used by default in earlier versions of Windows
> > > */
> > > if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL) {
> > > --
> > > 2.20.1
> > >
> >
>
>
> --
> Thanks,
>
> Steve

--
Thanks,

Steve

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In reply to: Steve French: "Re: [PATCH 6/7] cifs: Fix creating of SFU fifo and socket special files"
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