[17/23] sctp: Fix skb_over_panic resulting from multiple invalid parameter errors (CVE-2010-1173) (v4)

From: Greg KH
Date: Thu Jul 01 2010 - 14:12:18 EST

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2.6.27-stable review patch. If anyone has any objections, please let us know.

------------------

From: Neil Horman <nhorman@xxxxxxxxxxxxx>

commit 5fa782c2f5ef6c2e4f04d3e228412c9b4a4c8809 upstream.

Ok, version 4

Change Notes:
1) Minor cleanups, from Vlads notes

Summary:

Hey-
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
e0c2947d
<5> 00000000 00000080 df653490 00000004 de4f1ac0 de4f1ac0 00000004
df653490
<5> 00000001 e0c2877a 08000800 de4f1ac0 df653490 00000000 e0c29d2e
00000004
<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,
ntohs(chunk->chunk_hdr->length));

if (*errp) {
sctp_init_cause(*errp, SCTP_ERROR_UNKNOWN_PARAM,
WORD_ROUND(ntohs(param.p->length)));
sctp_addto_chunk(*errp,
WORD_ROUND(ntohs(param.p->length)),
param.v);

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:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=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: Neil Horman <nhorman@xxxxxxxxxxxxx>
Acked-by: Vlad Yasevich <vladislav.yasevich@xxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
include/net/sctp/structs.h | 1
net/sctp/sm_make_chunk.c | 62 +++++++++++++++++++++++++++++++++++++++++----
2 files changed, 58 insertions(+), 5 deletions(-)

--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -753,6 +753,7 @@ int sctp_user_addto_chunk(struct sctp_ch
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 *);
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -107,7 +107,7 @@ static const struct sctp_paramhdr prsctp
__constant_htons(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.
*/
@@ -124,6 +124,29 @@ void sctp_init_cause(struct sctp_chunk
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,
+ sizeof(sctp_errhdr_t),
+ &err);
+ return 0;
+}
/* 3.3.2 Initiation (INIT) (1)
*
* This chunk is used to initiate a SCTP association between two
@@ -1114,6 +1137,24 @@ nodata:
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)
+ size = SCTP_DEFAULT_MAXSEGMENT;
+
+ 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,
@@ -1354,6 +1395,18 @@ void *sctp_addto_chunk(struct sctp_chunk
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);
+ else
+ 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.
@@ -1957,13 +2010,12 @@ static sctp_ierror_t sctp_process_unk_pa
* returning multiple unknown parameters.
*/
if (NULL == *errp)
- *errp = sctp_make_op_error_space(asoc, chunk,
- ntohs(chunk->chunk_hdr->length));
+ *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,
WORD_ROUND(ntohs(param.p->length)));
- sctp_addto_chunk(*errp,
+ sctp_addto_chunk_fixed(*errp,
WORD_ROUND(ntohs(param.p->length)),
param.v);
} else {

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Next message: Greg KH: "[16/23] ext4: Implement range_cyclic in ext4_da_writepages instead of write_cache_pages"
Previous message: Greg KH: "[23/23] sctp: fix append error cause to ERROR chunk correctly"
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