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Date: Wed, 28 Apr 2010 16:37:04 -0400
From: Vlad Yasevich <vladislav.yasevich@...com>
To: Neil Horman <nhorman@...driver.com>
CC: sri@...ibm.com, linux-sctp@...r.kernel.org, eteo@...hat.com,
netdev@...r.kernel.org, davem@...emloft.net, security@...nel.org
Subject: Re: [PATCH]: sctp: Fix skb_over_panic resulting from multiple invalid
parameter errors (CVE-2010-1173) (v4)
Looks good.
Acked-by: Vlad Yasevich <vladislav.yasevich@...com>
-vlad
Neil Horman wrote:
> 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@...driver.com>
>
>
> include/net/sctp/structs.h | 1
> net/sctp/sm_make_chunk.c | 62 +++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 58 insertions(+), 5 deletions(-)
>
>
> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index ff30177..597f8e2 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -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 *);
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index f592163..2971731 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -107,7 +107,7 @@ 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.
> */
> @@ -124,6 +124,29 @@ 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,
> + sizeof(sctp_errhdr_t),
> + &err);
> + return 0;
> +}
> /* 3.3.2 Initiation (INIT) (1)
> *
> * This chunk is used to initiate a SCTP association between two
> @@ -1131,6 +1154,24 @@ 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,
> @@ -1373,6 +1414,18 @@ 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);
> + 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.
> @@ -1976,13 +2029,12 @@ 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,
> - 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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