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

Subsystems: networking [general], tc subsystem, the rest

STALE2038d

6 messages, 2 authors, 2021-01-14 · open the first message on its own page

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

From: Cong Wang <hidden>
Date: 2021-01-14 16:39:09 

From: Cong Wang <redacted>

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 <redacted>
---
 net/sched/cls_flower.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

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;
-- 
2.25.1

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

From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-01-14 18:39:35 

On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
From: Cong Wang <redacted>

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")
quoted hunk
@@ -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;





  

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

    

      From: Cong Wang <hidden>

      Date: 2021-01-14 20:04:26 
    

  

  
On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski [off-list ref] wrote:
On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
quoted
From: Cong Wang <redacted>

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")
quoted
@@ -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.

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

Thanks.





  

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

    

      From: Jakub Kicinski <kuba@kernel.org>

      Date: 2021-01-14 20:16:57 
    

  

  
On Thu, 14 Jan 2021 12:03:16 -0800 Cong Wang wrote:
On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski [off-list ref] wrote:
quoted
On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:  
quoted
From: Cong Wang <redacted>

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")  
 
quoted
@@ -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.





  

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

    

      From: Cong Wang <hidden>

      Date: 2021-01-14 20:25:13 
    

  

  
On Thu, Jan 14, 2021 at 12:16 PM Jakub Kicinski [off-list ref] wrote:
On Thu, 14 Jan 2021 12:03:16 -0800 Cong Wang wrote:
quoted
On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski [off-list ref] wrote:
quoted
On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
quoted
From: Cong Wang <redacted>

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")
quoted
@@ -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.





  

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

    

      From: Jakub Kicinski <kuba@kernel.org>

      Date: 2021-01-14 20:28:57 
    

  

  
On Thu, 14 Jan 2021 12:24:19 -0800 Cong Wang wrote:
quoted
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.




    
  

  
    

      

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