Commit 5fa782c2 authored by Neil Horman's avatar Neil Horman Committed by David S. Miller
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sctp: Fix skb_over_panic resulting from multiple invalid parameter errors (CVE-2010-1173) (v4)

Ok, version 4

Change Notes:
1) Minor cleanups, from Vlads notes


	Recently, it was reported to me that the kernel could oops in the
following way:

<5> kernel BUG at net/core/skbuff.c:91!
<5> invalid operand: 0000 [#1]
<5> Modules linked in: sctp netconsole nls_utf8 autofs4 sunrpc iptable_filter
ip_tables cpufreq_powersave parport_pc lp parport vmblock(U) vsock(U) vmci(U)
vmxnet(U) vmmemctl(U) vmhgfs(U) acpiphp dm_mirror dm_mod button battery ac md5
ipv6 uhci_hcd ehci_hcd snd_ens1371 snd_rawmidi snd_seq_device snd_pcm_oss
snd_mixer_oss snd_pcm snd_timer snd_page_alloc snd_ac97_codec snd soundcore
pcnet32 mii floppy ext3 jbd ata_piix libata mptscsih mptsas mptspi mptscsi
mptbase sd_mod scsi_mod
<5> CPU:    0
<5> EIP:    0060:[<c02bff27>]    Not tainted VLI
<5> EFLAGS: 00010216   (2.6.9-89.0.25.EL)
<5> EIP is at skb_over_panic+0x1f/0x2d
<5> eax: 0000002c   ebx: c033f461   ecx: c0357d96   edx: c040fd44
<5> esi: c033f461   edi: df653280   ebp: 00000000   esp: c040fd40
<5> ds: 007b   es: 007b   ss: 0068
<5> Process swapper (pid: 0, threadinfo=c040f000 task=c0370be0)
<5> Stack: c0357d96 e0c29478 00000084 00000004 c033f461 df653280 d7883180
<5>        00000000 00000080 df653490 00000004 de4f1ac0 de4f1ac0 00000004
<5>        00000001 e0c2877a 08000800 de4f1ac0 df653490 00000000 e0c29d2e
<5> Call Trace:
<5>  [<e0c29478>] sctp_addto_chunk+0xb0/0x128 [sctp]
<5>  [<e0c2947d>] sctp_addto_chunk+0xb5/0x128 [sctp]
<5>  [<e0c2877a>] sctp_init_cause+0x3f/0x47 [sctp]
<5>  [<e0c29d2e>] sctp_process_unk_param+0xac/0xb8 [sctp]
<5>  [<e0c29e90>] sctp_verify_init+0xcc/0x134 [sctp]
<5>  [<e0c20322>] sctp_sf_do_5_1B_init+0x83/0x28e [sctp]
<5>  [<e0c25333>] sctp_do_sm+0x41/0x77 [sctp]
<5>  [<c01555a4>] cache_grow+0x140/0x233
<5>  [<e0c26ba1>] sctp_endpoint_bh_rcv+0xc5/0x108 [sctp]
<5>  [<e0c2b863>] sctp_inq_push+0xe/0x10 [sctp]
<5>  [<e0c34600>] sctp_rcv+0x454/0x509 [sctp]
<5>  [<e084e017>] ipt_hook+0x17/0x1c [iptable_filter]
<5>  [<c02d005e>] nf_iterate+0x40/0x81
<5>  [<c02e0bb9>] ip_local_deliver_finish+0x0/0x151
<5>  [<c02e0c7f>] ip_local_deliver_finish+0xc6/0x151
<5>  [<c02d0362>] nf_hook_slow+0x83/0xb5
<5>  [<c02e0bb2>] ip_local_deliver+0x1a2/0x1a9
<5>  [<c02e0bb9>] ip_local_deliver_finish+0x0/0x151
<5>  [<c02e103e>] ip_rcv+0x334/0x3b4
<5>  [<c02c66fd>] netif_receive_skb+0x320/0x35b
<5>  [<e0a0928b>] init_stall_timer+0x67/0x6a [uhci_hcd]
<5>  [<c02c67a4>] process_backlog+0x6c/0xd9
<5>  [<c02c690f>] net_rx_action+0xfe/0x1f8
<5>  [<c012a7b1>] __do_softirq+0x35/0x79
<5>  [<c0107efb>] handle_IRQ_event+0x0/0x4f
<5>  [<c01094de>] do_softirq+0x46/0x4d

Its an skb_over_panic BUG halt that results from processing an init chunk in
which too many of its variable length parameters are in some way malformed.

The problem is in sctp_process_unk_param:
if (NULL == *errp)
	*errp = sctp_make_op_error_space(asoc, chunk,

	if (*errp) {
		sctp_init_cause(*errp, SCTP_ERROR_UNKNOWN_PARAM,

When we allocate an error chunk, we assume that the worst case scenario requires
that we have chunk_hdr->length data allocated, which would be correct nominally,
given that we call sctp_addto_chunk for the violating parameter.  Unfortunately,
we also, in sctp_init_cause insert a sctp_errhdr_t structure into the error
chunk, so the worst case situation in which all parameters are in violation
requires chunk_hdr->length+(sizeof(sctp_errhdr_t)*param_count) bytes of data.

The result of this error is that a deliberately malformed packet sent to a
listening host can cause a remote DOS, described in CVE-2010-1173:

I've tested the below fix and confirmed that it fixes the issue.  We move to a
strategy whereby we allocate a fixed size error chunk and ignore errors we don't
have space to report.  Tested by me successfully
Signed-off-by: default avatarNeil Horman <>
Acked-by: default avatarVlad Yasevich <>
Signed-off-by: default avatarDavid S. Miller <>
parent e41c11ee
......@@ -778,6 +778,7 @@ int sctp_user_addto_chunk(struct sctp_chunk *chunk, int off, int len,
struct iovec *data);
void sctp_chunk_free(struct sctp_chunk *);
void *sctp_addto_chunk(struct sctp_chunk *, int len, const void *data);
void *sctp_addto_chunk_fixed(struct sctp_chunk *, int len, const void *data);
struct sctp_chunk *sctp_chunkify(struct sk_buff *,
const struct sctp_association *,
struct sock *);
......@@ -108,7 +108,7 @@ static const struct sctp_paramhdr prsctp_param = {
cpu_to_be16(sizeof(struct sctp_paramhdr)),
/* A helper to initialize to initialize an op error inside a
/* A helper to initialize an op error inside a
* provided chunk, as most cause codes will be embedded inside an
* abort chunk.
......@@ -125,6 +125,29 @@ void sctp_init_cause(struct sctp_chunk *chunk, __be16 cause_code,
chunk->subh.err_hdr = sctp_addto_chunk(chunk, sizeof(sctp_errhdr_t), &err);
/* A helper to initialize an op error inside a
* provided chunk, as most cause codes will be embedded inside an
* abort chunk. Differs from sctp_init_cause in that it won't oops
* if there isn't enough space in the op error chunk
int sctp_init_cause_fixed(struct sctp_chunk *chunk, __be16 cause_code,
size_t paylen)
sctp_errhdr_t err;
__u16 len;
/* Cause code constants are now defined in network order. */
err.cause = cause_code;
len = sizeof(sctp_errhdr_t) + paylen;
err.length = htons(len);
if (skb_tailroom(chunk->skb) > len)
return -ENOSPC;
chunk->subh.err_hdr = sctp_addto_chunk_fixed(chunk,
return 0;
/* 3.3.2 Initiation (INIT) (1)
* This chunk is used to initiate a SCTP association between two
......@@ -1132,6 +1155,24 @@ static struct sctp_chunk *sctp_make_op_error_space(
return retval;
/* Create an Operation Error chunk of a fixed size,
* specifically, max(asoc->pathmtu, SCTP_DEFAULT_MAXSEGMENT)
* This is a helper function to allocate an error chunk for
* for those invalid parameter codes in which we may not want
* to report all the errors, if the incomming chunk is large
static inline struct sctp_chunk *sctp_make_op_error_fixed(
const struct sctp_association *asoc,
const struct sctp_chunk *chunk)
size_t size = asoc ? asoc->pathmtu : 0;
if (!size)
return sctp_make_op_error_space(asoc, chunk, size);
/* Create an Operation Error chunk. */
struct sctp_chunk *sctp_make_op_error(const struct sctp_association *asoc,
const struct sctp_chunk *chunk,
......@@ -1374,6 +1415,18 @@ void *sctp_addto_chunk(struct sctp_chunk *chunk, int len, const void *data)
return target;
/* Append bytes to the end of a chunk. Returns NULL if there isn't sufficient
* space in the chunk
void *sctp_addto_chunk_fixed(struct sctp_chunk *chunk,
int len, const void *data)
if (skb_tailroom(chunk->skb) > len)
return sctp_addto_chunk(chunk, len, data);
return NULL;
/* Append bytes from user space to the end of a chunk. Will panic if
* chunk is not big enough.
* Returns a kernel err value.
......@@ -1977,13 +2030,12 @@ static sctp_ierror_t sctp_process_unk_param(const struct sctp_association *asoc,
* returning multiple unknown parameters.
if (NULL == *errp)
*errp = sctp_make_op_error_space(asoc, chunk,
*errp = sctp_make_op_error_fixed(asoc, chunk);
if (*errp) {
sctp_init_cause(*errp, SCTP_ERROR_UNKNOWN_PARAM,
sctp_init_cause_fixed(*errp, SCTP_ERROR_UNKNOWN_PARAM,
} else {
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