Mercurial > dropbear
annotate fuzz/fuzzer-kexdh.c @ 1788:1fc0012b9c38
Fix handling of replies to global requests (#112)
The current code assumes that all global requests want / need a reply.
This isn't always true and the request itself indicates if it wants a
reply or not.
It causes a specific problem with [email protected] messages.
These are sent by OpenSSH after authentication to inform the client of
potential other host keys for the host. This can be used to add a new
type of host key or to rotate host keys.
The initial information message from the server is sent as a global
request, but with want_reply set to false. This means that the server
doesn't expect an answer to this message. Instead the client needs to
send a prove request as a reply if it wants to receive proof of
ownership for the host keys.
The bug doesn't cause any current problems with due to how OpenSSH
treats receiving the failure message. It instead treats it as a
keepalive message and further ignores it.
Arguably this is a protocol violation though of Dropbear and it is only
accidental that it doesn't cause a problem with OpenSSH.
The bug was found when adding host keys support to libssh, which is more
strict protocol wise and treats the unexpected failure message an error,
also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145
for more information.
The fix here is to honor the want_reply flag in the global request and
to only send a reply if the other side expects a reply.
| author | Dirkjan Bussink <d.bussink@gmail.com> |
|---|---|
| date | Thu, 10 Dec 2020 16:13:13 +0100 |
| parents | 0cc85b4a4abb |
| children |
| rev | line source |
|---|---|
| 1589 | 1 #include "fuzz.h" |
| 2 #include "session.h" | |
| 3 #include "fuzz-wrapfd.h" | |
| 4 #include "debug.h" | |
| 5 #include "runopts.h" | |
| 6 #include "algo.h" | |
| 7 #include "bignum.h" | |
| 8 | |
|
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0cc85b4a4abb
Move fuzzer-kex initialisation into a constructor function
Matt Johnston <matt@ucc.asn.au>
parents:
1756
diff
changeset
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9 static struct key_context* keep_newkeys = NULL; |
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0cc85b4a4abb
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Matt Johnston <matt@ucc.asn.au>
parents:
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10 #define NUM_PARAMS 80 |
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0cc85b4a4abb
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Matt Johnston <matt@ucc.asn.au>
parents:
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11 static struct kex_dh_param *dh_params[NUM_PARAMS]; |
| 1589 | 12 |
|
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parents:
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13 static void setup() __attribute__((constructor)); |
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Move fuzzer-kex initialisation into a constructor function
Matt Johnston <matt@ucc.asn.au>
parents:
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diff
changeset
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14 // Perform initial setup here to avoid hitting timeouts on first run |
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0cc85b4a4abb
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Matt Johnston <matt@ucc.asn.au>
parents:
1756
diff
changeset
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15 static void setup() { |
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parents:
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16 fuzz_common_setup(); |
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parents:
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17 fuzz_svr_setup(); |
| 1589 | 18 |
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parents:
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diff
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19 keep_newkeys = (struct key_context*)m_malloc(sizeof(struct key_context)); |
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Matt Johnston <matt@ucc.asn.au>
parents:
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20 keep_newkeys->algo_kex = fuzz_get_algo(sshkex, "diffie-hellman-group14-sha256"); |
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Matt Johnston <matt@ucc.asn.au>
parents:
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21 keep_newkeys->algo_hostkey = DROPBEAR_SIGNKEY_ECDSA_NISTP256; |
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Move fuzzer-kex initialisation into a constructor function
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parents:
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22 ses.newkeys = keep_newkeys; |
| 1589 | 23 |
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24 /* Pre-generate parameters */ |
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25 int i; |
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26 for (i = 0; i < NUM_PARAMS; i++) { |
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27 dh_params[i] = gen_kexdh_param(); |
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28 } |
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parents:
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29 } |
| 1589 | 30 |
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31 int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) { |
| 1589 | 32 if (fuzz_set_input(Data, Size) == DROPBEAR_FAILURE) { |
| 33 return 0; | |
| 34 } | |
| 35 | |
| 36 m_malloc_set_epoch(1); | |
| 37 | |
| 38 if (setjmp(fuzz.jmp) == 0) { | |
| 39 /* Based on recv_msg_kexdh_init()/send_msg_kexdh_reply() | |
| 40 with DROPBEAR_KEX_NORMAL_DH */ | |
| 41 ses.newkeys = keep_newkeys; | |
| 42 | |
| 43 /* Choose from the collection of ecdh params */ | |
| 44 unsigned int e = buf_getint(fuzz.input); | |
| 45 struct kex_dh_param * dh_param = dh_params[e % NUM_PARAMS]; | |
| 46 | |
| 47 DEF_MP_INT(dh_e); | |
| 48 m_mp_init(&dh_e); | |
| 49 if (buf_getmpint(fuzz.input, &dh_e) != DROPBEAR_SUCCESS) { | |
| 50 dropbear_exit("Bad kex value"); | |
| 51 } | |
| 52 | |
|
1606
98d2b125eb89
kexhashbuf was much to small in kex fuzzers
Matt Johnston <matt@ucc.asn.au>
parents:
1601
diff
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53 ses.kexhashbuf = buf_new(KEXHASHBUF_MAX_INTS); |
| 1589 | 54 kexdh_comb_key(dh_param, &dh_e, svr_opts.hostkey); |
| 55 | |
| 1609 | 56 mp_clear(ses.dh_K); |
| 1589 | 57 m_free(ses.dh_K); |
| 58 mp_clear(&dh_e); | |
| 59 | |
| 1609 | 60 buf_free(ses.hash); |
| 61 buf_free(ses.session_id); | |
| 62 /* kexhashbuf is freed in kexdh_comb_key */ | |
| 63 | |
| 1589 | 64 m_malloc_free_epoch(1, 0); |
| 65 } else { | |
| 66 m_malloc_free_epoch(1, 1); | |
| 67 TRACE(("dropbear_exit longjmped")) | |
| 68 /* dropbear_exit jumped here */ | |
| 69 } | |
| 70 | |
| 71 return 0; | |
| 72 } |