The recent refactoring of the IGMP and MLD parsing code into
ipv6_mc_check_mld() / ip_mc_check_igmp() introduced a potential crash /
BUG() invocation for bridges:
I wrongly assumed that skb_get() could be used as a simple reference
counter for an skb which is not the case. skb_get() bears additional
semantics, a user count. This leads to a BUG() invocation in
pskb_expand_head() / kernel panic if pskb_may_pull() is called on an skb
with a user count greater than one - unfortunately the refactoring did
just that.
Fixing this by removing the skb_get() call and changing the API: The
caller of ipv6_mc_check_mld() / ip_mc_check_igmp() now needs to
additionally check whether the returned skb_trimmed is a clone.
Fixes: 9afd85c9e455 ("net: Export IGMP/MLD message validation code")
Reported-by: Brenden Blanco <[email protected]>
Signed-off-by: Linus Lüssing <[email protected]>
---
net/bridge/br_multicast.c | 4 ++--
net/core/skbuff.c | 37 ++++++++++++++++++-------------------
net/ipv4/igmp.c | 33 ++++++++++++++++++---------------
net/ipv6/mcast_snoop.c | 33 ++++++++++++++++++---------------
4 files changed, 56 insertions(+), 51 deletions(-)
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 0b39dcc..1285eaf 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -1591,7 +1591,7 @@ static int br_multicast_ipv4_rcv(struct net_bridge *br,
break;
}
- if (skb_trimmed)
+ if (skb_trimmed && skb_trimmed != skb)
kfree_skb(skb_trimmed);
return err;
@@ -1636,7 +1636,7 @@ static int br_multicast_ipv6_rcv(struct net_bridge *br,
break;
}
- if (skb_trimmed)
+ if (skb_trimmed && skb_trimmed != skb)
kfree_skb(skb_trimmed);
return err;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index b6a19ca..bf9a5d9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4022,8 +4022,8 @@ EXPORT_SYMBOL(skb_checksum_setup);
* Otherwise returns the provided skb. Returns NULL in error cases
* (e.g. transport_len exceeds skb length or out-of-memory).
*
- * Caller needs to set the skb transport header and release the returned skb.
- * Provided skb is consumed.
+ * Caller needs to set the skb transport header and free any returned skb if it
+ * differs from the provided skb.
*/
static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
unsigned int transport_len)
@@ -4032,16 +4032,12 @@ static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
unsigned int len = skb_transport_offset(skb) + transport_len;
int ret;
- if (skb->len < len) {
- kfree_skb(skb);
+ if (skb->len < len)
return NULL;
- } else if (skb->len == len) {
+ else if (skb->len == len)
return skb;
- }
skb_chk = skb_clone(skb, GFP_ATOMIC);
- kfree_skb(skb);
-
if (!skb_chk)
return NULL;
@@ -4066,8 +4062,8 @@ static struct sk_buff *skb_checksum_maybe_trim(struct sk_buff *skb,
* If the skb has data beyond the given transport length, then a
* trimmed & cloned skb is checked and returned.
*
- * Caller needs to set the skb transport header and release the returned skb.
- * Provided skb is consumed.
+ * Caller needs to set the skb transport header and free any returned skb if it
+ * differs from the provided skb.
*/
struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
unsigned int transport_len,
@@ -4079,23 +4075,26 @@ struct sk_buff *skb_checksum_trimmed(struct sk_buff *skb,
skb_chk = skb_checksum_maybe_trim(skb, transport_len);
if (!skb_chk)
- return NULL;
+ goto err;
- if (!pskb_may_pull(skb_chk, offset)) {
- kfree_skb(skb_chk);
- return NULL;
- }
+ if (!pskb_may_pull(skb_chk, offset))
+ goto err;
__skb_pull(skb_chk, offset);
ret = skb_chkf(skb_chk);
__skb_push(skb_chk, offset);
- if (ret) {
- kfree_skb(skb_chk);
- return NULL;
- }
+ if (ret)
+ goto err;
return skb_chk;
+
+err:
+ if (skb_chk && skb_chk != skb)
+ kfree_skb(skb_chk);
+
+ return NULL;
+
}
EXPORT_SYMBOL(skb_checksum_trimmed);
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 651cdf6..9fdfd9d 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1435,33 +1435,35 @@ static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
struct sk_buff *skb_chk;
unsigned int transport_len;
unsigned int len = skb_transport_offset(skb) + sizeof(struct igmphdr);
- int ret;
+ int ret = -EINVAL;
transport_len = ntohs(ip_hdr(skb)->tot_len) - ip_hdrlen(skb);
- skb_get(skb);
skb_chk = skb_checksum_trimmed(skb, transport_len,
ip_mc_validate_checksum);
if (!skb_chk)
- return -EINVAL;
+ goto err;
- if (!pskb_may_pull(skb_chk, len)) {
- kfree_skb(skb_chk);
- return -EINVAL;
- }
+ if (!pskb_may_pull(skb_chk, len))
+ goto err;
ret = ip_mc_check_igmp_msg(skb_chk);
- if (ret) {
- kfree_skb(skb_chk);
- return ret;
- }
+ if (ret)
+ goto err;
if (skb_trimmed)
*skb_trimmed = skb_chk;
- else
+ /* free now unneeded clone */
+ else if (skb_chk != skb)
kfree_skb(skb_chk);
- return 0;
+ ret = 0;
+
+err:
+ if (ret && skb_chk && skb_chk != skb)
+ kfree_skb(skb_chk);
+
+ return ret;
}
/**
@@ -1470,7 +1472,7 @@ static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
* @skb_trimmed: to store an skb pointer trimmed to IPv4 packet tail (optional)
*
* Checks whether an IPv4 packet is a valid IGMP packet. If so sets
- * skb network and transport headers accordingly and returns zero.
+ * skb transport header accordingly and returns zero.
*
* -EINVAL: A broken packet was detected, i.e. it violates some internet
* standard
@@ -1485,7 +1487,8 @@ static int __ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
* to leave the original skb and its full frame unchanged (which might be
* desirable for layer 2 frame jugglers).
*
- * The caller needs to release a reference count from any returned skb_trimmed.
+ * Caller needs to set the skb network header and free any returned skb if it
+ * differs from the provided skb.
*/
int ip_mc_check_igmp(struct sk_buff *skb, struct sk_buff **skb_trimmed)
{
diff --git a/net/ipv6/mcast_snoop.c b/net/ipv6/mcast_snoop.c
index df8afe5..9405b04 100644
--- a/net/ipv6/mcast_snoop.c
+++ b/net/ipv6/mcast_snoop.c
@@ -143,34 +143,36 @@ static int __ipv6_mc_check_mld(struct sk_buff *skb,
struct sk_buff *skb_chk = NULL;
unsigned int transport_len;
unsigned int len = skb_transport_offset(skb) + sizeof(struct mld_msg);
- int ret;
+ int ret = -EINVAL;
transport_len = ntohs(ipv6_hdr(skb)->payload_len);
transport_len -= skb_transport_offset(skb) - sizeof(struct ipv6hdr);
- skb_get(skb);
skb_chk = skb_checksum_trimmed(skb, transport_len,
ipv6_mc_validate_checksum);
if (!skb_chk)
- return -EINVAL;
+ goto err;
- if (!pskb_may_pull(skb_chk, len)) {
- kfree_skb(skb_chk);
- return -EINVAL;
- }
+ if (!pskb_may_pull(skb_chk, len))
+ goto err;
ret = ipv6_mc_check_mld_msg(skb_chk);
- if (ret) {
- kfree_skb(skb_chk);
- return ret;
- }
+ if (ret)
+ goto err;
if (skb_trimmed)
*skb_trimmed = skb_chk;
- else
+ /* free now unneeded clone */
+ else if (skb_chk != skb)
kfree_skb(skb_chk);
- return 0;
+ ret = 0;
+
+err:
+ if (ret && skb_chk && skb_chk != skb)
+ kfree_skb(skb_chk);
+
+ return ret;
}
/**
@@ -179,7 +181,7 @@ static int __ipv6_mc_check_mld(struct sk_buff *skb,
* @skb_trimmed: to store an skb pointer trimmed to IPv6 packet tail (optional)
*
* Checks whether an IPv6 packet is a valid MLD packet. If so sets
- * skb network and transport headers accordingly and returns zero.
+ * skb transport header accordingly and returns zero.
*
* -EINVAL: A broken packet was detected, i.e. it violates some internet
* standard
@@ -194,7 +196,8 @@ static int __ipv6_mc_check_mld(struct sk_buff *skb,
* to leave the original skb and its full frame unchanged (which might be
* desirable for layer 2 frame jugglers).
*
- * The caller needs to release a reference count from any returned skb_trimmed.
+ * Caller needs to set the skb network header and free any returned skb if it
+ * differs from the provided skb.
*/
int ipv6_mc_check_mld(struct sk_buff *skb, struct sk_buff **skb_trimmed)
{
--
1.7.10.4
On Thu, Aug 13, 2015 at 05:54:07AM +0200, Linus L?ssing wrote:
> The recent refactoring of the IGMP and MLD parsing code into
> ipv6_mc_check_mld() / ip_mc_check_igmp() introduced a potential crash /
> BUG() invocation for bridges:
>
> I wrongly assumed that skb_get() could be used as a simple reference
> counter for an skb which is not the case. skb_get() bears additional
> semantics, a user count. This leads to a BUG() invocation in
> pskb_expand_head() / kernel panic if pskb_may_pull() is called on an skb
> with a user count greater than one - unfortunately the refactoring did
> just that.
>
> Fixing this by removing the skb_get() call and changing the API: The
> caller of ipv6_mc_check_mld() / ip_mc_check_igmp() now needs to
> additionally check whether the returned skb_trimmed is a clone.
>
> Fixes: 9afd85c9e455 ("net: Export IGMP/MLD message validation code")
> Reported-by: Brenden Blanco <[email protected]>
> Signed-off-by: Linus L?ssing <[email protected]>
I think the fix actually made the code easier to read.
Thank you. Looks good to me.
Acked-by: Alexei Starovoitov <[email protected]>
From: Linus L?ssing <[email protected]>
Date: Thu, 13 Aug 2015 05:54:07 +0200
> The recent refactoring of the IGMP and MLD parsing code into
> ipv6_mc_check_mld() / ip_mc_check_igmp() introduced a potential crash /
> BUG() invocation for bridges:
>
> I wrongly assumed that skb_get() could be used as a simple reference
> counter for an skb which is not the case. skb_get() bears additional
> semantics, a user count. This leads to a BUG() invocation in
> pskb_expand_head() / kernel panic if pskb_may_pull() is called on an skb
> with a user count greater than one - unfortunately the refactoring did
> just that.
>
> Fixing this by removing the skb_get() call and changing the API: The
> caller of ipv6_mc_check_mld() / ip_mc_check_igmp() now needs to
> additionally check whether the returned skb_trimmed is a clone.
>
> Fixes: 9afd85c9e455 ("net: Export IGMP/MLD message validation code")
> Reported-by: Brenden Blanco <[email protected]>
> Signed-off-by: Linus L?ssing <[email protected]>
Applied, thanks.