[PATCH] cifs: fix kref underflow in close_shroot()

[PATCH] cifs: fix kref underflow in close_shroot()

[Ronnie Sahlberg]

Fix a bug where we used to not initialize the cached fid structure at all
in open_shroot() if the open was successful but we did not get a lease.
This would leave the structure uninitialized and later when we close the handle
we would in close_shroot() try to kref_put() an uninitialized refcount.

Fix this by always initializing this structure if the open was successful
but only do the extra get() if we got a lease.
This extra get() is only used to hold the structure until we get a lease
break from the server at which point we will kref_put() it during lease
processing.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/smb2ops.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 1022a3771e14..7cfafac255aa 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -717,20 +717,18 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 	oparms.fid->mid = le64_to_cpu(o_rsp->sync_hdr.MessageId);
 #endif /* CIFS_DEBUG2 */
 
-	if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE)
-		oplock = smb2_parse_lease_state(server, o_rsp,
-						&oparms.fid->epoch,
-						oparms.fid->lease_key);
-	else
-		goto oshr_exit;
-
-
 	memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
 	tcon->crfid.tcon = tcon;
 	tcon->crfid.is_valid = true;
 	kref_init(&tcon->crfid.refcount);
-	kref_get(&tcon->crfid.refcount);
 
+	if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE) {
+		kref_get(&tcon->crfid.refcount);
+		oplock = smb2_parse_lease_state(server, o_rsp,
+						&oparms.fid->epoch,
+						oparms.fid->lease_key);
+	} else
+		goto oshr_exit;
 
 	qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
 	if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
-- 
2.13.6

Re: [PATCH] cifs: fix kref underflow in close_shroot()

[Steve French]

Should this be CC:stable?

On Wed, Mar 27, 2019 at 8:21 PM Ronnie Sahlberg <lsahlber@redhat.com> wrote:
>
> Fix a bug where we used to not initialize the cached fid structure at all
> in open_shroot() if the open was successful but we did not get a lease.
> This would leave the structure uninitialized and later when we close the handle
> we would in close_shroot() try to kref_put() an uninitialized refcount.
>
> Fix this by always initializing this structure if the open was successful
> but only do the extra get() if we got a lease.
> This extra get() is only used to hold the structure until we get a lease
> break from the server at which point we will kref_put() it during lease
> processing.
>
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/smb2ops.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 1022a3771e14..7cfafac255aa 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -717,20 +717,18 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
>         oparms.fid->mid = le64_to_cpu(o_rsp->sync_hdr.MessageId);
>  #endif /* CIFS_DEBUG2 */
>
> -       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE)
> -               oplock = smb2_parse_lease_state(server, o_rsp,
> -                                               &oparms.fid->epoch,
> -                                               oparms.fid->lease_key);
> -       else
> -               goto oshr_exit;
> -
> -
>         memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
>         tcon->crfid.tcon = tcon;
>         tcon->crfid.is_valid = true;
>         kref_init(&tcon->crfid.refcount);
> -       kref_get(&tcon->crfid.refcount);
>
> +       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE) {
> +               kref_get(&tcon->crfid.refcount);
> +               oplock = smb2_parse_lease_state(server, o_rsp,
> +                                               &oparms.fid->epoch,
> +                                               oparms.fid->lease_key);
> +       } else
> +               goto oshr_exit;
>
>         qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
>         if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
> --
> 2.13.6
>


-- 
Thanks,

Steve

Re: [PATCH] cifs: fix kref underflow in close_shroot()

[ronnie sahlberg]

Yeah, probably

On Thu, Mar 28, 2019 at 3:11 PM Steve French <smfrench@gmail.com> wrote:
>
> Should this be CC:stable?
>
> On Wed, Mar 27, 2019 at 8:21 PM Ronnie Sahlberg <lsahlber@redhat.com> wrote:
> >
> > Fix a bug where we used to not initialize the cached fid structure at all
> > in open_shroot() if the open was successful but we did not get a lease.
> > This would leave the structure uninitialized and later when we close the handle
> > we would in close_shroot() try to kref_put() an uninitialized refcount.
> >
> > Fix this by always initializing this structure if the open was successful
> > but only do the extra get() if we got a lease.
> > This extra get() is only used to hold the structure until we get a lease
> > break from the server at which point we will kref_put() it during lease
> > processing.
> >
> > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > ---
> >  fs/cifs/smb2ops.c | 16 +++++++---------
> >  1 file changed, 7 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> > index 1022a3771e14..7cfafac255aa 100644
> > --- a/fs/cifs/smb2ops.c
> > +++ b/fs/cifs/smb2ops.c
> > @@ -717,20 +717,18 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> >         oparms.fid->mid = le64_to_cpu(o_rsp->sync_hdr.MessageId);
> >  #endif /* CIFS_DEBUG2 */
> >
> > -       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE)
> > -               oplock = smb2_parse_lease_state(server, o_rsp,
> > -                                               &oparms.fid->epoch,
> > -                                               oparms.fid->lease_key);
> > -       else
> > -               goto oshr_exit;
> > -
> > -
> >         memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
> >         tcon->crfid.tcon = tcon;
> >         tcon->crfid.is_valid = true;
> >         kref_init(&tcon->crfid.refcount);
> > -       kref_get(&tcon->crfid.refcount);
> >
> > +       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE) {
> > +               kref_get(&tcon->crfid.refcount);
> > +               oplock = smb2_parse_lease_state(server, o_rsp,
> > +                                               &oparms.fid->epoch,
> > +                                               oparms.fid->lease_key);
> > +       } else
> > +               goto oshr_exit;
> >
> >         qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
> >         if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
> > --
> > 2.13.6
> >
>
>
> --
> Thanks,
>
> Steve

Re: [PATCH] cifs: fix kref underflow in close_shroot()

[Pavel Shilovsky]

ср, 27 мар. 2019 г. в 22:27, ronnie sahlberg <ronniesahlberg@gmail.com>:
>
> Yeah, probably
>
> On Thu, Mar 28, 2019 at 3:11 PM Steve French <smfrench@gmail.com> wrote:
> >
> > Should this be CC:stable?
> >
> > On Wed, Mar 27, 2019 at 8:21 PM Ronnie Sahlberg <lsahlber@redhat.com> wrote:
> > >
> > > Fix a bug where we used to not initialize the cached fid structure at all
> > > in open_shroot() if the open was successful but we did not get a lease.
> > > This would leave the structure uninitialized and later when we close the handle
> > > we would in close_shroot() try to kref_put() an uninitialized refcount.
> > >
> > > Fix this by always initializing this structure if the open was successful
> > > but only do the extra get() if we got a lease.
> > > This extra get() is only used to hold the structure until we get a lease
> > > break from the server at which point we will kref_put() it during lease
> > > processing.
> > >
> > > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > > ---
> > >  fs/cifs/smb2ops.c | 16 +++++++---------
> > >  1 file changed, 7 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> > > index 1022a3771e14..7cfafac255aa 100644
> > > --- a/fs/cifs/smb2ops.c
> > > +++ b/fs/cifs/smb2ops.c
> > > @@ -717,20 +717,18 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> > >         oparms.fid->mid = le64_to_cpu(o_rsp->sync_hdr.MessageId);
> > >  #endif /* CIFS_DEBUG2 */
> > >
> > > -       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE)
> > > -               oplock = smb2_parse_lease_state(server, o_rsp,
> > > -                                               &oparms.fid->epoch,
> > > -                                               oparms.fid->lease_key);
> > > -       else
> > > -               goto oshr_exit;
> > > -
> > > -
> > >         memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
> > >         tcon->crfid.tcon = tcon;
> > >         tcon->crfid.is_valid = true;
> > >         kref_init(&tcon->crfid.refcount);
> > > -       kref_get(&tcon->crfid.refcount);
> > >
> > > +       if (o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE) {
> > > +               kref_get(&tcon->crfid.refcount);
> > > +               oplock = smb2_parse_lease_state(server, o_rsp,
> > > +                                               &oparms.fid->epoch,
> > > +                                               oparms.fid->lease_key);
> > > +       } else
> > > +               goto oshr_exit;
> > >
> > >         qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
> > >         if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
> > > --
> > > 2.13.6
> > >
> >
> >
> > --
> > Thanks,
> >
> > Steve

This part of the fix looks good but there is another piece remaining:

rc = smb2_validate_and_copy_iov(
    le16_to_cpu(qi_rsp->OutputBufferOffset),
    sizeof(struct smb2_file_all_info),
    &rsp_iov[1], sizeof(struct smb2_file_all_info),
    (char *)&tcon->crfid.file_all_info);
if (rc)
    goto oshr_exit;
    ^^^
here RC is non-zero, but we are returning with 2 references on the
handle. The caller will assume that the open failed and doesn't call
close_shroot thus leaking one reference.

The result of smb2_validate_and_copy_iov only affects file_all_info
caching but doesn't affect the handle validity. So, RC needs to be
reset to 0 unconditionally here before returning from the function.

I checked v5.0 kernel and it doesn't seem it is affected by this bug
but it has the problem that it doesn't check whether server granted
the lease or not - probably it is not that bad to keep the reference
forever for non-leased opens, so leaving it for your choice to fix it
or not.

--
Best regards,
Pavel Shilovsky

Re: [PATCH] cifs: fix kref underflow in close_shroot()

[ronnie sahlberg]

On Thu, Mar 28, 2019 at 10:17 AM Pavel Shilovsky <piastryyy@gmail.com> wrote:
>
> ср, 27 мар. 2019 г. в 16:58, Ronnie Sahlberg <lsahlber@redhat.com>:
> >
> > Fix a bug where we used to not initialize the cached fid structure at all
> > in open_shroot() if the open was successful but we did not get a lease.
> > This would leave the structure uninitialized and later when we close the handle
> > we would in close_shroot() try to kref_put() an uninitialized refcount.
> >
> > Fix this by always initializing this structure when we are about to return
> > 0/success but make the extra kref_get() on the refcount conditional to
> > whether we got a lease or not.
> > This extra get() is only used to hold the structure until we get a lease
> > break from the server at which point we will kref_put() it during lease
> > processing.
> >
> > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > ---
> >  fs/cifs/smb2ops.c | 22 ++++++++++++++--------
> >  1 file changed, 14 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> > index 1022a3771e14..4f0fb53cd0de 100644
> > --- a/fs/cifs/smb2ops.c
> > +++ b/fs/cifs/smb2ops.c
> > @@ -724,14 +724,6 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> >         else
> >                 goto oshr_exit;
> >
> > -
> > -       memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
> > -       tcon->crfid.tcon = tcon;
> > -       tcon->crfid.is_valid = true;
> > -       kref_init(&tcon->crfid.refcount);
> > -       kref_get(&tcon->crfid.refcount);
> > -
> > -
> >         qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
> >         if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
> >                 goto oshr_exit;
> > @@ -745,6 +737,20 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
> >         tcon->crfid.file_all_info_is_valid = 1;
> >
> >   oshr_exit:
> > +       /*
> > +        * If we return 0/success then we must also initialize this struct.
> > +        * If we got a lease we need to take out an extra get() to keep
> > +        * the structure around until we receive the actual lease break.
> > +        */
> > +       if (rc == 0) {
>             ^^^
> This will still leak a handle if smb2_validate_and_copy_iov failed above.

Right. I will resend.
>
> --
> Best regards,
> Pavel Shilovsky

Re: [PATCH] cifs: fix kref underflow in close_shroot()

[Pavel Shilovsky]

ср, 27 мар. 2019 г. в 16:58, Ronnie Sahlberg <lsahlber@redhat.com>:
>
> Fix a bug where we used to not initialize the cached fid structure at all
> in open_shroot() if the open was successful but we did not get a lease.
> This would leave the structure uninitialized and later when we close the handle
> we would in close_shroot() try to kref_put() an uninitialized refcount.
>
> Fix this by always initializing this structure when we are about to return
> 0/success but make the extra kref_get() on the refcount conditional to
> whether we got a lease or not.
> This extra get() is only used to hold the structure until we get a lease
> break from the server at which point we will kref_put() it during lease
> processing.
>
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/smb2ops.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index 1022a3771e14..4f0fb53cd0de 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -724,14 +724,6 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
>         else
>                 goto oshr_exit;
>
> -
> -       memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
> -       tcon->crfid.tcon = tcon;
> -       tcon->crfid.is_valid = true;
> -       kref_init(&tcon->crfid.refcount);
> -       kref_get(&tcon->crfid.refcount);
> -
> -
>         qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
>         if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
>                 goto oshr_exit;
> @@ -745,6 +737,20 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
>         tcon->crfid.file_all_info_is_valid = 1;
>
>   oshr_exit:
> +       /*
> +        * If we return 0/success then we must also initialize this struct.
> +        * If we got a lease we need to take out an extra get() to keep
> +        * the structure around until we receive the actual lease break.
> +        */
> +       if (rc == 0) {
            ^^^
This will still leak a handle if smb2_validate_and_copy_iov failed above.

--
Best regards,
Pavel Shilovsky

[PATCH] cifs: fix kref underflow in close_shroot()

[Ronnie Sahlberg]

Fix a bug where we used to not initialize the cached fid structure at all
in open_shroot() if the open was successful but we did not get a lease.
This would leave the structure uninitialized and later when we close the handle
we would in close_shroot() try to kref_put() an uninitialized refcount.

Fix this by always initializing this structure when we are about to return
0/success but make the extra kref_get() on the refcount conditional to
whether we got a lease or not.
This extra get() is only used to hold the structure until we get a lease
break from the server at which point we will kref_put() it during lease
processing.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/smb2ops.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index 1022a3771e14..4f0fb53cd0de 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -724,14 +724,6 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 	else
 		goto oshr_exit;
 
-
-	memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
-	tcon->crfid.tcon = tcon;
-	tcon->crfid.is_valid = true;
-	kref_init(&tcon->crfid.refcount);
-	kref_get(&tcon->crfid.refcount);
-
-
 	qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
 	if (le32_to_cpu(qi_rsp->OutputBufferLength) < sizeof(struct smb2_file_all_info))
 		goto oshr_exit;
@@ -745,6 +737,20 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
 	tcon->crfid.file_all_info_is_valid = 1;
 
  oshr_exit:
+	/*
+	 * If we return 0/success then we must also initialize this struct.
+	 * If we got a lease we need to take out an extra get() to keep
+	 * the structure around until we receive the actual lease break.
+	 */
+	if (rc == 0) {
+		memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
+		tcon->crfid.tcon = tcon;
+		tcon->crfid.is_valid = true;
+		kref_init(&tcon->crfid.refcount);
+		if (o_rsp && o_rsp->OplockLevel == SMB2_OPLOCK_LEVEL_LEASE)
+			kref_get(&tcon->crfid.refcount);
+	}
+
 	mutex_unlock(&tcon->crfid.fid_mutex);
 	SMB2_open_free(&rqst[0]);
 	SMB2_query_info_free(&rqst[1]);
-- 
2.13.6