| Message ID | 20230927164715.76744-3-joao@overdrivepizza.com (mailing list archive) |
|---|---|
| State | Awaiting Upstream |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | Prevent potential write out of bounds | expand |
On Wed, Sep 27, 2023 at 09:47:15AM -0700, joao@overdrivepizza.com wrote: > From: Joao Moreira <joao.moreira@intel.com> > > Currently, in nft_flow_rule_create function, num_actions is a signed > integer. Yet, it is processed within a loop which increments its > value. To prevent an overflow from occurring, make it unsigned and > also check if it reaches 256 when being incremented. > > Accordingly to discussions around v2, 256 actions are more than enough > for the frontend actions. > > After checking with maintainers, it was mentioned that front-end will > cap the num_actions value and that it is not possible to reach such > condition for an overflow. Yet, for correctness, it is still better to > fix this. > > This issue was observed by the commit author while reviewing a write-up > regarding a CVE within the same subsystem [1]. > > 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/ Yes, but this is not related to the netfilter subsystem itself, this harderning is good to have for the flow offload infrastructure in general. > Signed-off-by: Joao Moreira <joao.moreira@intel.com> > --- > net/netfilter/nf_tables_offload.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c > index 12ab78fa5d84..9a86db1f0e07 100644 > --- a/net/netfilter/nf_tables_offload.c > +++ b/net/netfilter/nf_tables_offload.c > @@ -90,7 +90,8 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net, > { > struct nft_offload_ctx *ctx; > struct nft_flow_rule *flow; > - int num_actions = 0, err; > + unsigned int num_actions = 0; > + int err; reverse xmas tree. > struct nft_expr *expr; > > expr = nft_expr_first(rule); > @@ -99,6 +100,10 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net, > expr->ops->offload_action(expr)) > num_actions++; > > + /* 2^8 is enough for frontend actions, avoid overflow */ > + if (num_actions == 256) This cap is not specific of nf_tables, it should apply to all other subsystems. This is the wrong spot. Moreover, please, add a definition for this, no hardcoded values. > + return ERR_PTR(-ENOMEM); Better E2BIG or similar, otherwise this propagates to userspace as ENOMEM. > + > expr = nft_expr_next(expr); > } > > -- > 2.42.0 >
On 2023-09-28 06:43, Pablo Neira Ayuso wrote: > On Wed, Sep 27, 2023 at 09:47:15AM -0700, joao@overdrivepizza.com > wrote: >> From: Joao Moreira <joao.moreira@intel.com> >> >> Currently, in nft_flow_rule_create function, num_actions is a signed >> integer. Yet, it is processed within a loop which increments its >> value. To prevent an overflow from occurring, make it unsigned and >> also check if it reaches 256 when being incremented. >> >> Accordingly to discussions around v2, 256 actions are more than enough >> for the frontend actions. >> >> After checking with maintainers, it was mentioned that front-end will >> cap the num_actions value and that it is not possible to reach such >> condition for an overflow. Yet, for correctness, it is still better to >> fix this. >> >> This issue was observed by the commit author while reviewing a >> write-up >> regarding a CVE within the same subsystem [1]. >> >> 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/ > > Yes, but this is not related to the netfilter subsystem itself, this > harderning is good to have for the flow offload infrastructure in > general. Right, I'll try to look up where this would fit in then. I'm not an expert in the subsystem at all, so should take a minute or two for me to get to it and send a v4. > >> Signed-off-by: Joao Moreira <joao.moreira@intel.com> >> --- >> net/netfilter/nf_tables_offload.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/net/netfilter/nf_tables_offload.c >> b/net/netfilter/nf_tables_offload.c >> index 12ab78fa5d84..9a86db1f0e07 100644 >> --- a/net/netfilter/nf_tables_offload.c >> +++ b/net/netfilter/nf_tables_offload.c >> @@ -90,7 +90,8 @@ struct nft_flow_rule *nft_flow_rule_create(struct >> net *net, >> { >> struct nft_offload_ctx *ctx; >> struct nft_flow_rule *flow; >> - int num_actions = 0, err; >> + unsigned int num_actions = 0; >> + int err; > > reverse xmas tree. ack. > >> struct nft_expr *expr; >> >> expr = nft_expr_first(rule); >> @@ -99,6 +100,10 @@ struct nft_flow_rule *nft_flow_rule_create(struct >> net *net, >> expr->ops->offload_action(expr)) >> num_actions++; >> >> + /* 2^8 is enough for frontend actions, avoid overflow */ >> + if (num_actions == 256) > > This cap is not specific of nf_tables, it should apply to all other > subsystems. This is the wrong spot. Any pointers regarding where I should look at? > > Moreover, please, add a definition for this, no hardcoded values. Ack. > >> + return ERR_PTR(-ENOMEM); > > Better E2BIG or similar, otherwise this propagates to userspace as > ENOMEM. Ack. > >> + >> expr = nft_expr_next(expr); >> } >> >> -- >> 2.42.0 >>
On Thu, Sep 28, 2023 at 07:55:09PM -0700, Joao Moreira wrote: > On 2023-09-28 06:43, Pablo Neira Ayuso wrote: > > On Wed, Sep 27, 2023 at 09:47:15AM -0700, joao@overdrivepizza.com wrote: > > > From: Joao Moreira <joao.moreira@intel.com> > > > > > > Currently, in nft_flow_rule_create function, num_actions is a signed > > > integer. Yet, it is processed within a loop which increments its > > > value. To prevent an overflow from occurring, make it unsigned and > > > also check if it reaches 256 when being incremented. > > > > > > Accordingly to discussions around v2, 256 actions are more than enough > > > for the frontend actions. > > > > > > After checking with maintainers, it was mentioned that front-end will > > > cap the num_actions value and that it is not possible to reach such > > > condition for an overflow. Yet, for correctness, it is still better to > > > fix this. > > > > > > This issue was observed by the commit author while reviewing a > > > write-up > > > regarding a CVE within the same subsystem [1]. > > > > > > 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/ > > > > Yes, but this is not related to the netfilter subsystem itself, this > > harderning is good to have for the flow offload infrastructure in > > general. > > Right, I'll try to look up where this would fit in then. I'm not an expert > in the subsystem at all, so should take a minute or two for me to get to it > and send a v4. Thanks. > > > struct nft_expr *expr; > > > > > > expr = nft_expr_first(rule); > > > @@ -99,6 +100,10 @@ struct nft_flow_rule > > > *nft_flow_rule_create(struct net *net, > > > expr->ops->offload_action(expr)) > > > num_actions++; > > > > > > + /* 2^8 is enough for frontend actions, avoid overflow */ > > > + if (num_actions == 256) > > > > This cap is not specific of nf_tables, it should apply to all other > > subsystems. This is the wrong spot. > > Any pointers regarding where I should look at? See flow_rule_alloc().
diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c index 12ab78fa5d84..9a86db1f0e07 100644 --- a/net/netfilter/nf_tables_offload.c +++ b/net/netfilter/nf_tables_offload.c @@ -90,7 +90,8 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net, { struct nft_offload_ctx *ctx; struct nft_flow_rule *flow; - int num_actions = 0, err; + unsigned int num_actions = 0; + int err; struct nft_expr *expr; expr = nft_expr_first(rule); @@ -99,6 +100,10 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net, expr->ops->offload_action(expr)) num_actions++; + /* 2^8 is enough for frontend actions, avoid overflow */ + if (num_actions == 256) + return ERR_PTR(-ENOMEM); + expr = nft_expr_next(expr); }