diff mbox series

[net,v2] cls_flower: call nla_ok() before nla_next()

Message ID 20210114163822.56306-1-xiyou.wangcong@gmail.com
State Superseded
Headers show
Series [net,v2] cls_flower: call nla_ok() before nla_next() | expand

Commit Message

Cong Wang Jan. 14, 2021, 4:38 p.m. UTC
From: Cong Wang <cong.wang@bytedance.com>

fl_set_enc_opt() simply checks if there are still bytes left to parse,
but this is not sufficent as syzbot seems to be able to generate
malformatted netlink messages. nla_ok() is more strict so should be
used to validate the next nlattr here.

And nla_validate_nested_deprecated() has less strict check too, it is
probably too late to switch to the strict version, but we can just
call nla_ok() too after it.

Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Xin Long <lucien.xin@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
---
 net/sched/cls_flower.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

Comments

Jakub Kicinski Jan. 14, 2021, 6:38 p.m. UTC | #1
On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
> From: Cong Wang <cong.wang@bytedance.com>
> 
> fl_set_enc_opt() simply checks if there are still bytes left to parse,
> but this is not sufficent as syzbot seems to be able to generate
> malformatted netlink messages. nla_ok() is more strict so should be
> used to validate the next nlattr here.
> 
> And nla_validate_nested_deprecated() has less strict check too, it is
> probably too late to switch to the strict version, but we can just
> call nla_ok() too after it.
> 
> Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
> Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
> Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")

> @@ -1340,9 +1341,6 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
>  				NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
>  				return -EINVAL;
>  			}
> -
> -			if (msk_depth)
> -				nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
>  			break;
>  		case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
>  			if (key->enc_opts.dst_opt_type) {
> @@ -1373,14 +1371,17 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
>  				NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
>  				return -EINVAL;
>  			}
> -
> -			if (msk_depth)
> -				nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
>  			break;
>  		default:
>  			NL_SET_ERR_MSG(extack, "Unknown tunnel option type");
>  			return -EINVAL;
>  		}
> +
> +		if (!nla_ok(nla_opt_msk, msk_depth)) {
> +			NL_SET_ERR_MSG(extack, "Mask attribute is invalid");
> +			return -EINVAL;
> +		}
> +		nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);

we lost the if (msk_depth) now, nla_opt_msk may be NULL -
neither nla_ok() nor nla_next() take NULL

>  	}
>  
>  	return 0;
Jakub Kicinski Jan. 14, 2021, 8:16 p.m. UTC | #2
On Thu, 14 Jan 2021 12:03:16 -0800 Cong Wang wrote:
> On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:  
> > > From: Cong Wang <cong.wang@bytedance.com>
> > >
> > > fl_set_enc_opt() simply checks if there are still bytes left to parse,
> > > but this is not sufficent as syzbot seems to be able to generate
> > > malformatted netlink messages. nla_ok() is more strict so should be
> > > used to validate the next nlattr here.
> > >
> > > And nla_validate_nested_deprecated() has less strict check too, it is
> > > probably too late to switch to the strict version, but we can just
> > > call nla_ok() too after it.
> > >
> > > Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
> > > Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
> > > Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")  
> >  
> > > @@ -1340,9 +1341,6 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
> > >                               NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
> > >                               return -EINVAL;
> > >                       }
> > > -
> > > -                     if (msk_depth)
> > > -                             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > >                       break;
> > >               case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
> > >                       if (key->enc_opts.dst_opt_type) {
> > > @@ -1373,14 +1371,17 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
> > >                               NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
> > >                               return -EINVAL;
> > >                       }
> > > -
> > > -                     if (msk_depth)
> > > -                             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > >                       break;
> > >               default:
> > >                       NL_SET_ERR_MSG(extack, "Unknown tunnel option type");
> > >                       return -EINVAL;
> > >               }
> > > +
> > > +             if (!nla_ok(nla_opt_msk, msk_depth)) {
> > > +                     NL_SET_ERR_MSG(extack, "Mask attribute is invalid");
> > > +                     return -EINVAL;
> > > +             }
> > > +             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);  
> >
> > we lost the if (msk_depth) now, nla_opt_msk may be NULL -
> > neither nla_ok() nor nla_next() take NULL  
> 
> How is "if (msk_depth)" lost when nla_ok() has a stricter one?
> 
> 1156 static inline int nla_ok(const struct nlattr *nla, int remaining)
> 1157 {
> 1158         return remaining >= (int) sizeof(*nla) &&
> 1159                nla->nla_len >= sizeof(*nla) &&
> 1160                nla->nla_len <= remaining;
> 1161 }
> 
> Line 1156 assures msk_depth is not only non-zero but also larger
> than the nla struct size, and clearly nla won't be dereferenced unless
> this check is passed.

Fair, depth will but 0 so first check already fails, but nla_next()
would crash since it tries to access the length of the attribute
unconditionally.

> I guess you mean we should not error out for nla_opt_msk==NULL
> case as masks are optional?

Yup.
Cong Wang Jan. 14, 2021, 8:24 p.m. UTC | #3
On Thu, Jan 14, 2021 at 12:16 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 14 Jan 2021 12:03:16 -0800 Cong Wang wrote:
> > On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski <kuba@kernel.org> wrote:
> > >
> > > On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
> > > > From: Cong Wang <cong.wang@bytedance.com>
> > > >
> > > > fl_set_enc_opt() simply checks if there are still bytes left to parse,
> > > > but this is not sufficent as syzbot seems to be able to generate
> > > > malformatted netlink messages. nla_ok() is more strict so should be
> > > > used to validate the next nlattr here.
> > > >
> > > > And nla_validate_nested_deprecated() has less strict check too, it is
> > > > probably too late to switch to the strict version, but we can just
> > > > call nla_ok() too after it.
> > > >
> > > > Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
> > > > Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
> > > > Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")
> > >
> > > > @@ -1340,9 +1341,6 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
> > > >                               NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
> > > >                               return -EINVAL;
> > > >                       }
> > > > -
> > > > -                     if (msk_depth)
> > > > -                             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > > >                       break;
> > > >               case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
> > > >                       if (key->enc_opts.dst_opt_type) {
> > > > @@ -1373,14 +1371,17 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
> > > >                               NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
> > > >                               return -EINVAL;
> > > >                       }
> > > > -
> > > > -                     if (msk_depth)
> > > > -                             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > > >                       break;
> > > >               default:
> > > >                       NL_SET_ERR_MSG(extack, "Unknown tunnel option type");
> > > >                       return -EINVAL;
> > > >               }
> > > > +
> > > > +             if (!nla_ok(nla_opt_msk, msk_depth)) {
> > > > +                     NL_SET_ERR_MSG(extack, "Mask attribute is invalid");
> > > > +                     return -EINVAL;
> > > > +             }
> > > > +             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > >
> > > we lost the if (msk_depth) now, nla_opt_msk may be NULL -
> > > neither nla_ok() nor nla_next() take NULL
> >
> > How is "if (msk_depth)" lost when nla_ok() has a stricter one?
> >
> > 1156 static inline int nla_ok(const struct nlattr *nla, int remaining)
> > 1157 {
> > 1158         return remaining >= (int) sizeof(*nla) &&
> > 1159                nla->nla_len >= sizeof(*nla) &&
> > 1160                nla->nla_len <= remaining;
> > 1161 }
> >
> > Line 1156 assures msk_depth is not only non-zero but also larger
> > than the nla struct size, and clearly nla won't be dereferenced unless
> > this check is passed.
>
> Fair, depth will but 0 so first check already fails, but nla_next()
> would crash since it tries to access the length of the attribute
> unconditionally.

nla_next() is only called when nla_ok() returns true, which is not
the case for msk_depth==0, therefore NULL won't crash here.

The only problem is we become too strict to reject optionally missing
masks, we should not even call nla_ok() here, otherwise it would
break user-space. So,

+               if (!nla_opt_msk)
+                       continue;

Thanks.
Jakub Kicinski Jan. 14, 2021, 8:27 p.m. UTC | #4
On Thu, 14 Jan 2021 12:24:19 -0800 Cong Wang wrote:
> > Fair, depth will but 0 so first check already fails, but nla_next()
> > would crash since it tries to access the length of the attribute
> > unconditionally.  
> 
> nla_next() is only called when nla_ok() returns true, which is not
> the case for msk_depth==0, therefore NULL won't crash here.
> 
> The only problem is we become too strict to reject optionally missing
> masks, we should not even call nla_ok() here, otherwise it would
> break user-space. So,
> 
> +               if (!nla_opt_msk)
> +                       continue;
> 
> Thanks.

You're right.
diff mbox series

Patch

diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index 1319986693fc..740d9018e45f 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -1272,6 +1272,10 @@  static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
 
 		nla_opt_msk = nla_data(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
 		msk_depth = nla_len(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
+		if (!nla_ok(nla_opt_msk, msk_depth)) {
+			NL_SET_ERR_MSG(extack, "Invalid attribute for masks");
+			return -EINVAL;
+		}
 	}
 
 	nla_for_each_attr(nla_opt_key, nla_enc_key,
@@ -1307,9 +1311,6 @@  static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
 				NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
 				return -EINVAL;
 			}
-
-			if (msk_depth)
-				nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
 			break;
 		case TCA_FLOWER_KEY_ENC_OPTS_VXLAN:
 			if (key->enc_opts.dst_opt_type) {
@@ -1340,9 +1341,6 @@  static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
 				NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
 				return -EINVAL;
 			}
-
-			if (msk_depth)
-				nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
 			break;
 		case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
 			if (key->enc_opts.dst_opt_type) {
@@ -1373,14 +1371,17 @@  static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
 				NL_SET_ERR_MSG(extack, "Key and mask miss aligned");
 				return -EINVAL;
 			}
-
-			if (msk_depth)
-				nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
 			break;
 		default:
 			NL_SET_ERR_MSG(extack, "Unknown tunnel option type");
 			return -EINVAL;
 		}
+
+		if (!nla_ok(nla_opt_msk, msk_depth)) {
+			NL_SET_ERR_MSG(extack, "Mask attribute is invalid");
+			return -EINVAL;
+		}
+		nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
 	}
 
 	return 0;