From 5fa782c2f5ef6c2e4f04d3e228412c9b4a4c8809 Mon Sep 17 00:00:00 2001 From: Neil Horman Date: Wed, 28 Apr 2010 10:30:59 +0000 Subject: 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 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:[] 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> [] sctp_addto_chunk+0xb0/0x128 [sctp] <5> [] sctp_addto_chunk+0xb5/0x128 [sctp] <5> [] sctp_init_cause+0x3f/0x47 [sctp] <5> [] sctp_process_unk_param+0xac/0xb8 [sctp] <5> [] sctp_verify_init+0xcc/0x134 [sctp] <5> [] sctp_sf_do_5_1B_init+0x83/0x28e [sctp] <5> [] sctp_do_sm+0x41/0x77 [sctp] <5> [] cache_grow+0x140/0x233 <5> [] sctp_endpoint_bh_rcv+0xc5/0x108 [sctp] <5> [] sctp_inq_push+0xe/0x10 [sctp] <5> [] sctp_rcv+0x454/0x509 [sctp] <5> [] ipt_hook+0x17/0x1c [iptable_filter] <5> [] nf_iterate+0x40/0x81 <5> [] ip_local_deliver_finish+0x0/0x151 <5> [] ip_local_deliver_finish+0xc6/0x151 <5> [] nf_hook_slow+0x83/0xb5 <5> [] ip_local_deliver+0x1a2/0x1a9 <5> [] ip_local_deliver_finish+0x0/0x151 <5> [] ip_rcv+0x334/0x3b4 <5> [] netif_receive_skb+0x320/0x35b <5> [] init_stall_timer+0x67/0x6a [uhci_hcd] <5> [] process_backlog+0x6c/0xd9 <5> [] net_rx_action+0xfe/0x1f8 <5> [] __do_softirq+0x35/0x79 <5> [] handle_IRQ_event+0x0/0x4f <5> [] 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 Acked-by: Vlad Yasevich Signed-off-by: David S. Miller 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 0fd5b4c..30c1767 100644 --- a/net/sctp/sm_make_chunk.c +++ b/net/sctp/sm_make_chunk.c @@ -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, + sizeof(sctp_errhdr_t), + &err); + return 0; +} /* 3.3.2 Initiation (INIT) (1) * * This chunk is used to initiate a SCTP association between two @@ -1132,6 +1155,24 @@ 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, @@ -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); + 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. @@ -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, - 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 { -- cgit v0.10.2