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net: fix wrong skb_get() usage / crash in IGMP/MLD parsing code

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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: 9afd85c9e4 ("net: Export IGMP/MLD message validation code")
Reported-by: Brenden Blanco <bblanco@plumgrid.com>
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Linus Lüssing 2015-08-13 05:54:07 +02:00 committed by David S. Miller
parent 5b3e2e14ea
commit a516993f0a
4 changed files with 56 additions and 51 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

4
net/bridge/br_multicast.c
View file

@ -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;

37
net/core/skbuff.c
View file

@ -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);

33
net/ipv4/igmp.c
View file

@ -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)
{

33
net/ipv6/mcast_snoop.c
View file

@ -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)
{