From 4c5a5879f75bda99f9f4ad266ddd0e095ab1cdc8 Mon Sep 17 00:00:00 2001 From: Donald Sharp Date: Thu, 10 Oct 2019 08:52:54 -0400 Subject: [PATCH] lib: Fix read beyond end of data structure Our Address Sanitizer CI is finding this issue: error 09-Oct-2019 19:28:33 r4: bgpd triggered an exception by AddressSanitizer error 09-Oct-2019 19:28:33 ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffdd425b060 at pc 0x00000068575f bp 0x7ffdd4258550 sp 0x7ffdd4258540 error 09-Oct-2019 19:28:33 READ of size 1 at 0x7ffdd425b060 thread T0 error 09-Oct-2019 19:28:33 #0 0x68575e in prefix_cmp lib/prefix.c:776 error 09-Oct-2019 19:28:33 #1 0x5889f5 in rfapiItBiIndexSearch bgpd/rfapi/rfapi_import.c:2230 error 09-Oct-2019 19:28:33 #2 0x5889f5 in rfapiBgpInfoFilteredImportVPN bgpd/rfapi/rfapi_import.c:3520 error 09-Oct-2019 19:28:33 #3 0x58b909 in rfapiProcessWithdraw bgpd/rfapi/rfapi_import.c:4071 error 09-Oct-2019 19:28:33 #4 0x4c459b in bgp_withdraw bgpd/bgp_route.c:3736 error 09-Oct-2019 19:28:33 #5 0x484122 in bgp_nlri_parse_vpn bgpd/bgp_mplsvpn.c:237 error 09-Oct-2019 19:28:33 #6 0x497f52 in bgp_nlri_parse bgpd/bgp_packet.c:315 error 09-Oct-2019 19:28:33 #7 0x49d06d in bgp_update_receive bgpd/bgp_packet.c:1598 error 09-Oct-2019 19:28:33 #8 0x49d06d in bgp_process_packet bgpd/bgp_packet.c:2274 error 09-Oct-2019 19:28:33 #9 0x6b9f54 in thread_call lib/thread.c:1531 error 09-Oct-2019 19:28:33 #10 0x657037 in frr_run lib/libfrr.c:1052 error 09-Oct-2019 19:28:33 #11 0x42d268 in main bgpd/bgp_main.c:486 error 09-Oct-2019 19:28:33 #12 0x7f806032482f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f) error 09-Oct-2019 19:28:33 #13 0x42bcc8 in _start (/usr/lib/frr/bgpd+0x42bcc8) error 09-Oct-2019 19:28:33 error 09-Oct-2019 19:28:33 Address 0x7ffdd425b060 is located in stack of thread T0 at offset 240 in frame error 09-Oct-2019 19:28:33 #0 0x483945 in bgp_nlri_parse_vpn bgpd/bgp_mplsvpn.c:103 error 09-Oct-2019 19:28:33 error 09-Oct-2019 19:28:33 This frame has 5 object(s): error 09-Oct-2019 19:28:33 [32, 36) 'label' error 09-Oct-2019 19:28:33 [96, 108) 'rd_as' error 09-Oct-2019 19:28:33 [160, 172) 'rd_ip' error 09-Oct-2019 19:28:33 [224, 240) 'prd' <== Memory access at offset 240 overflows this variable error 09-Oct-2019 19:28:33 [288, 336) 'p' error 09-Oct-2019 19:28:33 HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext error 09-Oct-2019 19:28:33 (longjmp and C++ exceptions *are* supported) error 09-Oct-2019 19:28:33 SUMMARY: AddressSanitizer: stack-buffer-overflow lib/prefix.c:776 prefix_cmp error 09-Oct-2019 19:28:33 Shadow bytes around the buggy address: error 09-Oct-2019 19:28:33 0x10003a8435b0: 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00 00 error 09-Oct-2019 19:28:33 0x10003a8435c0: 00 00 00 00 00 00 00 00 00 00 f3 f3 f3 f3 f3 f3 error 09-Oct-2019 19:28:33 0x10003a8435d0: f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 error 09-Oct-2019 19:28:33 0x10003a8435e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 error 09-Oct-2019 19:28:33 0x10003a8435f0: f1 f1 04 f4 f4 f4 f2 f2 f2 f2 00 04 f4 f4 f2 f2 error 09-Oct-2019 19:28:33 =>0x10003a843600: f2 f2 00 04 f4 f4 f2 f2 f2 f2 00 00[f4]f4 f2 f2 error 09-Oct-2019 19:28:33 0x10003a843610: f2 f2 00 00 00 00 00 00 f4 f4 f3 f3 f3 f3 00 00 error 09-Oct-2019 19:28:33 0x10003a843620: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 error 09-Oct-2019 19:28:33 0x10003a843630: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 02 f4 error 09-Oct-2019 19:28:33 0x10003a843640: f4 f4 f2 f2 f2 f2 04 f4 f4 f4 f2 f2 f2 f2 00 00 error 09-Oct-2019 19:28:33 0x10003a843650: f4 f4 f2 f2 f2 f2 00 00 00 00 f2 f2 f2 f2 00 00 error 09-Oct-2019 19:28:33 Shadow byte legend (one shadow byte represents 8 application bytes): error 09-Oct-2019 19:28:33 Addressable: 00 error 09-Oct-2019 19:28:33 Partially addressable: 01 02 03 04 05 06 07 error 09-Oct-2019 19:28:33 Heap left redzone: fa error 09-Oct-2019 19:28:33 Heap right redzone: fb error 09-Oct-2019 19:28:33 Freed heap region: fd error 09-Oct-2019 19:28:33 Stack left redzone: f1 error 09-Oct-2019 19:28:33 Stack mid redzone: f2 error 09-Oct-2019 19:28:33 Stack right redzone: f3 error 09-Oct-2019 19:28:33 Stack partial redzone: f4 error 09-Oct-2019 19:28:33 Stack after return: f5 error 09-Oct-2019 19:28:33 Stack use after scope: f8 error 09-Oct-2019 19:28:33 Global redzone: f9 error 09-Oct-2019 19:28:33 Global init order: f6 error 09-Oct-2019 19:28:33 Poisoned by user: f7 error 09-Oct-2019 19:28:33 Container overflow: fc error 09-Oct-2019 19:28:33 Array cookie: ac error 09-Oct-2019 19:28:33 Intra object redzone: bb error 09-Oct-2019 19:28:33 ASan internal: fe error 09-Oct-2019 19:28:36 r3: Daemon bgpd not running This is the result of this code pattern in rfapi/rfapi_import.c: prefix_cmp((struct prefix *)&bpi_result->extra->vnc.import.rd, (struct prefix *)prd)) Effectively prd or vnc.import.rd are `struct prefix_rd` which are being typecast to a `struct prefix`. Not a big deal except commit 1315d74de97be2944d7b005b2f9a50e9ae5eff4d modified the prefix_cmp function to allow for a sorted prefix_cmp. In prefix_cmp we were looking at the offset and shift. In the case of vnc we were passing a prefix length of 64 which is the exact length of the remaining data structure for struct prefix_rd. So we calculated a offset of 8 and a shift of 0. The data structures for the prefix portion happened to be equal to 64 bits of data. So we checked that with the memcmp got a 0 and promptly read off the end of the data structure for the numcmp. The fix is if shift is 0 that means thei the memcmp has checked everything and there is nothing to do. Please note: We will still crash if we set the prefixlen > then ~312 bits currently( ie if the prefixlen specifies a bit length longer than the prefix length ). I do not think there is anything to do here( nor am I sure how to correct this either ) as that we are going to have some severe problems when we muck up the prefixlen. Fixes: #5025 Signed-off-by: Donald Sharp --- lib/prefix.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/lib/prefix.c b/lib/prefix.c index 35b679ab90fb..aa6661d7fb79 100644 --- a/lib/prefix.c +++ b/lib/prefix.c @@ -773,8 +773,18 @@ int prefix_cmp(union prefixconstptr up1, union prefixconstptr up2) if (i) return i; - return numcmp(pp1[offset] & maskbit[shift], - pp2[offset] & maskbit[shift]); + /* + * At this point offset was the same, if we have shift + * that means we still have data to compare, if shift is + * 0 then we are at the end of the data structure + * and should just return, as that we will be accessing + * memory beyond the end of the party zone + */ + if (shift) + return numcmp(pp1[offset] & maskbit[shift], + pp2[offset] & maskbit[shift]); + + return 0; } /*