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ee576c47db
The icmp{,v6}_send functions make all sorts of use of skb->cb, casting
it with IPCB or IP6CB, assuming the skb to have come directly from the
inet layer. But when the packet comes from the ndo layer, especially
when forwarded, there's no telling what might be in skb->cb at that
point. As a result, the icmp sending code risks reading bogus memory
contents, which can result in nasty stack overflows such as this one
reported by a user:
panic+0x108/0x2ea
__stack_chk_fail+0x14/0x20
__icmp_send+0x5bd/0x5c0
icmp_ndo_send+0x148/0x160
In icmp_send, skb->cb is cast with IPCB and an ip_options struct is read
from it. The optlen parameter there is of particular note, as it can
induce writes beyond bounds. There are quite a few ways that can happen
in __ip_options_echo. For example:
// sptr/skb are attacker-controlled skb bytes
sptr = skb_network_header(skb);
// dptr/dopt points to stack memory allocated by __icmp_send
dptr = dopt->__data;
// sopt is the corrupt skb->cb in question
if (sopt->rr) {
optlen = sptr[sopt->rr+1]; // corrupt skb->cb + skb->data
soffset = sptr[sopt->rr+2]; // corrupt skb->cb + skb->data
// this now writes potentially attacker-controlled data, over
// flowing the stack:
memcpy(dptr, sptr+sopt->rr, optlen);
}
In the icmpv6_send case, the story is similar, but not as dire, as only
IP6CB(skb)->iif and IP6CB(skb)->dsthao are used. The dsthao case is
worse than the iif case, but it is passed to ipv6_find_tlv, which does
a bit of bounds checking on the value.
This is easy to simulate by doing a `memset(skb->cb, 0x41,
sizeof(skb->cb));` before calling icmp{,v6}_ndo_send, and it's only by
good fortune and the rarity of icmp sending from that context that we've
avoided reports like this until now. For example, in KASAN:
BUG: KASAN: stack-out-of-bounds in __ip_options_echo+0xa0e/0x12b0
Write of size 38 at addr ffff888006f1f80e by task ping/89
CPU: 2 PID: 89 Comm: ping Not tainted 5.10.0-rc7-debug+ #5
Call Trace:
dump_stack+0x9a/0xcc
print_address_description.constprop.0+0x1a/0x160
__kasan_report.cold+0x20/0x38
kasan_report+0x32/0x40
check_memory_region+0x145/0x1a0
memcpy+0x39/0x60
__ip_options_echo+0xa0e/0x12b0
__icmp_send+0x744/0x1700
Actually, out of the 4 drivers that do this, only gtp zeroed the cb for
the v4 case, while the rest did not. So this commit actually removes the
gtp-specific zeroing, while putting the code where it belongs in the
shared infrastructure of icmp{,v6}_ndo_send.
This commit fixes the issue by passing an empty IPCB or IP6CB along to
the functions that actually do the work. For the icmp_send, this was
already trivial, thanks to __icmp_send providing the plumbing function.
For icmpv6_send, this required a tiny bit of refactoring to make it
behave like the v4 case, after which it was straight forward.
Fixes: a2b78e9b2c ("sunvnet: generate ICMP PTMUD messages for smaller port MTUs")
Reported-by: SinYu <liuxyon@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://lore.kernel.org/netdev/CAF=yD-LOF116aHub6RMe8vB8ZpnrrnoTdqhobEx+bvoA8AsP0w@mail.gmail.com/T/
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://lore.kernel.org/r/20210223131858.72082-1-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
107 lines
2.7 KiB
C
107 lines
2.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_ICMPV6_H
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#define _LINUX_ICMPV6_H
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#include <linux/skbuff.h>
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#include <linux/ipv6.h>
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#include <uapi/linux/icmpv6.h>
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static inline struct icmp6hdr *icmp6_hdr(const struct sk_buff *skb)
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{
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return (struct icmp6hdr *)skb_transport_header(skb);
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}
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#include <linux/netdevice.h>
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#if IS_ENABLED(CONFIG_IPV6)
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typedef void ip6_icmp_send_t(struct sk_buff *skb, u8 type, u8 code, __u32 info,
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const struct in6_addr *force_saddr,
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const struct inet6_skb_parm *parm);
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void icmp6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
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const struct in6_addr *force_saddr,
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const struct inet6_skb_parm *parm);
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#if IS_BUILTIN(CONFIG_IPV6)
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static inline void __icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
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const struct inet6_skb_parm *parm)
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{
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icmp6_send(skb, type, code, info, NULL, parm);
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}
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static inline int inet6_register_icmp_sender(ip6_icmp_send_t *fn)
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{
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BUILD_BUG_ON(fn != icmp6_send);
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return 0;
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}
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static inline int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn)
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{
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BUILD_BUG_ON(fn != icmp6_send);
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return 0;
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}
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#else
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extern void __icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info,
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const struct inet6_skb_parm *parm);
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extern int inet6_register_icmp_sender(ip6_icmp_send_t *fn);
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extern int inet6_unregister_icmp_sender(ip6_icmp_send_t *fn);
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#endif
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static inline void icmpv6_send(struct sk_buff *skb, u8 type, u8 code, __u32 info)
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{
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__icmpv6_send(skb, type, code, info, IP6CB(skb));
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}
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int ip6_err_gen_icmpv6_unreach(struct sk_buff *skb, int nhs, int type,
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unsigned int data_len);
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#if IS_ENABLED(CONFIG_NF_NAT)
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void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info);
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#else
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static inline void icmpv6_ndo_send(struct sk_buff *skb_in, u8 type, u8 code, __u32 info)
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{
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struct inet6_skb_parm parm = { 0 };
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__icmpv6_send(skb_in, type, code, info, &parm);
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}
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#endif
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#else
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static inline void icmpv6_send(struct sk_buff *skb,
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u8 type, u8 code, __u32 info)
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{
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}
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static inline void icmpv6_ndo_send(struct sk_buff *skb,
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u8 type, u8 code, __u32 info)
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{
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}
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#endif
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extern int icmpv6_init(void);
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extern int icmpv6_err_convert(u8 type, u8 code,
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int *err);
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extern void icmpv6_cleanup(void);
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extern void icmpv6_param_prob(struct sk_buff *skb,
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u8 code, int pos);
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struct flowi6;
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struct in6_addr;
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extern void icmpv6_flow_init(struct sock *sk,
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struct flowi6 *fl6,
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u8 type,
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const struct in6_addr *saddr,
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const struct in6_addr *daddr,
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int oif);
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static inline bool icmpv6_is_err(int type)
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{
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switch (type) {
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case ICMPV6_DEST_UNREACH:
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case ICMPV6_PKT_TOOBIG:
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case ICMPV6_TIME_EXCEED:
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case ICMPV6_PARAMPROB:
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return true;
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}
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return false;
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}
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#endif
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