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[2016-01-28 09:42 UTC] shm@php.net
Description: ------------ http://lxr.php.net/xref/PHP_7_0/ext/openssl/openssl.c#4890: 4888/* {{{ proto int openssl_seal(string data, &string sealdata, &array ekeys, array pubkeys) 4889 Seals data */ 4890PHP_FUNCTION(openssl_seal) 4891{ 4892 zval *pubkeys, *pubkey, *sealdata, *ekeys, *iv = NULL; 4893 HashTable *pubkeysht; 4894 EVP_PKEY **pkeys; [...] 4895 zend_resource ** key_resources; /* so we know what to cleanup */ 4905 if (zend_parse_parameters(ZEND_NUM_ARGS(), "sz/z/a/|sz/", &data, &data_len, 4906 &sealdata, &ekeys, &pubkeys, &method, &method_len, &iv) == FAILURE) { 4907 return; 4908 } 4909 pubkeysht = Z_ARRVAL_P(pubkeys); 4910 nkeys = pubkeysht ? zend_hash_num_elements(pubkeysht) : 0; 4911 if (!nkeys) { 4912 php_error_docref(NULL, E_WARNING, "Fourth argument to openssl_seal() must be a non-empty array"); 4913 RETURN_FALSE; 4914 } [...] 4935 pkeys = safe_emalloc(nkeys, sizeof(*pkeys), 0); [...] 4939 key_resources = safe_emalloc(nkeys, sizeof(zend_resource*), 0); 4940 memset(key_resources, 0, sizeof(zend_resource*) * nkeys); 4941 4942 /* get the public keys we are using to seal this data */ 4943 i = 0; 4944 ZEND_HASH_FOREACH_VAL(pubkeysht, pubkey) { 4945 pkeys[i] = php_openssl_evp_from_zval(pubkey, 1, NULL, 0, &key_resources[i]); 4946 if (pkeys[i] == NULL) { 4947 php_error_docref(NULL, E_WARNING, "not a public key (%dth member of pubkeys)", i+1); 4948 RETVAL_FALSE; 4949 goto clean_exit; 4950 } 4951 eks[i] = emalloc(EVP_PKEY_size(pkeys[i]) + 1); 4952 i++; 4953 } ZEND_HASH_FOREACH_END(); [...] 5000clean_exit: 5001 for (i=0; i<nkeys; i++) { 5002 if (key_resources[i] == NULL) { 5003 EVP_PKEY_free(pkeys[i]); 5004 } [...] 5008 } Let's analyze this function, in line 4939 code allocates key_resources table followed by zeroing it, this table is used to mark keys that are intended to be freed. key_resources table is filled by loop between lines 4944 and 4953. nkeys is a number of elements passed to the function in pubkeys array. Now if one of the array members is not a valid public key, then code goes to clean_exit routine that iterates over key_resources table and frees pkeys structures. pkeys itself is not initialized - loop starting in 4944 line is supposed to do so, but in case of firing up clean_exit we end up with uninitialized part of the array. Now let's recall that key_resources was zeroed, it means that we're going to call EVAP_PKEY_free() on uninitialized pkeys members. The bug was introduced by commit 424aebbf3643b3fc1b1074ecddf2104cb9465f02 [1], quick review confirms that it affects branch 7.x only, so most distros are safe as they let cook 7.x branch for a while. # Is it exploitable? Well, it depends what EVP_PKEY_free does, so let's see the implementation: [http://nxr.netbsd.org/xref/src/crypto/external/bsd/openssl/dist/crypto/evp/p_lib.c#376] 376 void EVP_PKEY_free(EVP_PKEY *x) 377 { 378 int i; 379 380 if (x == NULL) 381 return; 382 383 i = CRYPTO_add(&x->references, -1, CRYPTO_LOCK_EVP_PKEY); [...] 387 if (i > 0) 388 return; [...] 395 EVP_PKEY_free_it(x); 396 if (x->attributes) 397 sk_X509_ATTRIBUTE_pop_free(x->attributes, X509_ATTRIBUTE_free); 398 OPENSSL_free(x); 399 } Thanks to x == NULL check it wasn't found by unit tests. One obvious way to exploit this bug is to trigger double free and then try to mess up something, but OpenSSL uses allocator from libc which usually deals with double free pretty well. There's an option to manipulate memory via CRYPTO_add (as we control x), but decreasing by 1 will not get us far. Let's dig deeper and see the EVP_PKEY_free_it() implementation: http://nxr.netbsd.org/xref/src/crypto/external/bsd/openssl/dist/crypto/evp/p_lib.c#EVP_PKEY_free_it 401 static void EVP_PKEY_free_it(EVP_PKEY *x) 402 { 403 if (x->ameth && x->ameth->pkey_free) { 404 x->ameth->pkey_free(x); 405 x->pkey.ptr = NULL; 406 } [...] 404 line contains call to pkey_free(), address of which is extracted from x pointer and comes from uninitialized memory, which under some circumstances we control. Therefore, it can gain us code execution! Simple crash PoC: ~/src/php-7.0.2/sapi/cli$ gdb ./php [...] (gdb) r -r 'str_repeat("A", 512); openssl_seal($_, $_, $_, array_fill(0,64,0));' Starting program: /home/rj4/src/php-7.0.2/sapi/cli/php -r 'str_repeat("A", 512); openssl_seal($_, $_, $_, array_fill(0,64,0));' [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". Warning: openssl_seal(): not a public key (1th member of pubkeys) in Command line code on line 1 Program received signal SIGSEGV, Segmentation fault. 0x00007ffff5a3d837 in CRYPTO_add_lock () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (gdb) x/i $rip => 0x7ffff5a3d837 <CRYPTO_add_lock+71>: add (%r12),%r13d (gdb) i r [...] r12 0x208 520 [...] (gdb) up #1 0x00007ffff5ad0199 in EVP_PKEY_free () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (gdb) #2 0x00000000004f0d12 in zif_openssl_seal (execute_data=0x7ffff28130d0, return_value=0x7ffff28130c0) at /home/rj4/src/php-7.0.2/ext/openssl/openssl.c:5003 5003 EVP_PKEY_free(pkeys[i]); (gdb) print i $3 = 2 (gdb) print pkeys[i] $11 = (EVP_PKEY *) 0x200 (gdb) print pkeys[i+1] $12 = (EVP_PKEY *) 0x4141414141414141 (gdb) print pkeys[i+2] $13 = (EVP_PKEY *) 0x4141414141414141 Patch: openssl_seal(): } pkeys = safe_emalloc(nkeys, sizeof(*pkeys), 0); - memset(pkeys, 0, sizeof(*pkeys) * nkeys); eksl = safe_emalloc(nkeys, sizeof(*eksl), 0); eks = safe_emalloc(nkeys, sizeof(*eks), 0); memset(eks, 0, sizeof(*eks) * nkeys); Test script: --------------- <?php str_repeat("A", 512); openssl_seal($_, $_, $_, array_fill(0,64,0)); Expected result: ---------------- PHP does not crash Actual result: -------------- (gdb) r -r 'str_repeat("A", 512); openssl_seal($_, $_, $_, array_fill(0,64,0));' Starting program: /home/rj4/src/php-7.0.2/sapi/cli/php -r 'str_repeat("A", 512); openssl_seal($_, $_, $_, array_fill(0,64,0));' [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". Warning: openssl_seal(): not a public key (1th member of pubkeys) in Command line code on line 1 Program received signal SIGSEGV, Segmentation fault. 0x00007ffff5a3d837 in CRYPTO_add_lock () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (gdb) x/i $rip => 0x7ffff5a3d837 <CRYPTO_add_lock+71>: add (%r12),%r13d (gdb) i r [...] r12 0x208 520 [...] (gdb) up #1 0x00007ffff5ad0199 in EVP_PKEY_free () from /lib/x86_64-linux-gnu/libcrypto.so.1.0.0 (gdb) #2 0x00000000004f0d12 in zif_openssl_seal (execute_data=0x7ffff28130d0, return_value=0x7ffff28130c0) at /home/rj4/src/php-7.0.2/ext/openssl/openssl.c:5003 5003 EVP_PKEY_free(pkeys[i]); (gdb) print i $3 = 2 (gdb) print pkeys[i] $11 = (EVP_PKEY *) 0x200 (gdb) print pkeys[i+1] $12 = (EVP_PKEY *) 0x4141414141414141 (gdb) print pkeys[i+2] $13 = (EVP_PKEY *) 0x4141414141414141 PatchesPull RequestsHistoryAllCommentsChangesGit/SVN commits
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Last updated: Thu Nov 21 10:01:29 2024 UTC |
Just clarify - I mean to do this: diff --git a/ext/openssl/openssl.c b/ext/openssl/openssl.c index 04ac7e5..5bdc46c 100644 --- a/ext/openssl/openssl.c +++ b/ext/openssl/openssl.c @@ -5316,7 +5316,7 @@ PHP_FUNCTION(openssl_seal) clean_exit: for (i=0; i<nkeys; i++) { - if (key_resources[i] == NULL && pkeys[i] != NULL) { + if (pkeys[i] != NULL) { EVP_PKEY_free(pkeys[i]); } if (eks[i]) {From the report [...] The bug was introduced by commit 424aebbf3643b3fc1b1074ecddf2104cb9465f02 [1], quick review confirms that it affects branch 7.x only, so most distros are safe as they let cook 7.x branch for a while. [...] So branch 5.x is not affected. ---- bukka@, what about: 4939 pkeys = safe_emalloc(nkeys, sizeof(*pkeys), 0); 4940 eksl = safe_emalloc(nkeys, sizeof(*eksl), 0); 4941 eks = safe_emalloc(nkeys, sizeof(*eks), 0); 4942 memset(eks, 0, sizeof(*eks) * nkeys); 4943 key_resources = safe_emalloc(nkeys, sizeof(zend_resource*), 0); 4944 memset(key_resources, 0, sizeof(zend_resource*) * nkeys); 4945 memset(pkeys, 0, sizeof(*pkeys) * nkeys); transforming this to ecalloc. diff --git a/ext/openssl/openssl.c b/ext/openssl/openssl.c index 04ac7e5..5bdc46c 100644 --- a/ext/openssl/openssl.c +++ b/ext/openssl/openssl.c @@ -5316,7 +5316,7 @@ PHP_FUNCTION(openssl_seal) clean_exit: for (i=0; i<nkeys; i++) { - if (key_resources[i] == NULL && pkeys[i] != NULL) { + if (pkeys[i] != NULL) { EVP_PKEY_free(pkeys[i]); } if (eks[i]) { I think that this is wrong, why we keep key_resources table then?