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Move obfuscate_name out of winshare.c.
Now it lives in wincapi.c (under a slightly less generic name), so it can be reused in other contexts.
This commit is contained in:
Simon Tatham
parent
58e2a35bdf
commit
e305974313
@ -6,6 +6,9 @@
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#if !defined NO_SECURITY
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#include "putty.h"
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#include "ssh.h"
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#define WINCAPI_GLOBAL
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#include "wincapi.h"
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@ -31,4 +34,78 @@ bool got_crypt(void)
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return successful;
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}
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#ifdef COVERITY
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/*
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* The hack I use to build for Coverity scanning, using winegcc and
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* Makefile.mgw, didn't provide some defines in wincrypt.h last time I
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* looked. Therefore, define them myself here, but enclosed in #ifdef
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* COVERITY to ensure I don't make up random nonsense values for any
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* real build.
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*/
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#ifndef CRYPTPROTECTMEMORY_BLOCK_SIZE
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#define CRYPTPROTECTMEMORY_BLOCK_SIZE 16
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#endif
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#ifndef CRYPTPROTECTMEMORY_CROSS_PROCESS
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#define CRYPTPROTECTMEMORY_CROSS_PROCESS 1
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#endif
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#endif
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char *capi_obfuscate_string(const char *realname)
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{
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char *cryptdata;
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int cryptlen;
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unsigned char digest[32];
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char retbuf[65];
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int i;
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cryptlen = strlen(realname) + 1;
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cryptlen += CRYPTPROTECTMEMORY_BLOCK_SIZE - 1;
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cryptlen /= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptlen *= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptdata = snewn(cryptlen, char);
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memset(cryptdata, 0, cryptlen);
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strcpy(cryptdata, realname);
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/*
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* CRYPTPROTECTMEMORY_CROSS_PROCESS causes CryptProtectMemory to
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* use the same key in all processes with this user id, meaning
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* that the next PuTTY process calling this function with the same
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* input will get the same data.
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*
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* (Contrast with CryptProtectData, which invents a new session
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* key every time since its API permits returning more data than
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* was input, so calling _that_ and hashing the output would not
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* be stable.)
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*
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* We don't worry too much if this doesn't work for some reason.
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* Omitting this step still has _some_ privacy value (in that
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* another user can test-hash things to confirm guesses as to
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* where you might be connecting to, but cannot invert SHA-256 in
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* the absence of any plausible guess). So we don't abort if we
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* can't call CryptProtectMemory at all, or if it fails.
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*/
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if (got_crypt())
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p_CryptProtectMemory(cryptdata, cryptlen,
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CRYPTPROTECTMEMORY_CROSS_PROCESS);
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/*
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* We don't want to give away the length of the hostname either,
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* so having got it back out of CryptProtectMemory we now hash it.
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*/
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hash_simple(&ssh_sha256, make_ptrlen(cryptdata, cryptlen), digest);
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sfree(cryptdata);
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/*
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* Finally, make printable.
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*/
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for (i = 0; i < 32; i++) {
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sprintf(retbuf + 2*i, "%02x", digest[i]);
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/* the last of those will also write the trailing NUL */
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}
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return dupstr(retbuf);
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}
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#endif /* !defined NO_SECURITY */
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@ -1,7 +1,8 @@
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/*
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* wincapi.h: Windows Crypto API functions defined in wincrypt.c
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* that use the crypt32 library. Also centralises the machinery
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* for dynamically loading that library.
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* wincapi.h: Windows Crypto API functions defined in wincapi.c that
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* use the crypt32 library. Also centralises the machinery for
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* dynamically loading that library, and our own functions using that
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* in turn.
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*/
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#if !defined NO_SECURITY
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@ -15,4 +16,21 @@ DECL_WINDOWS_FUNCTION(WINCAPI_GLOBAL, BOOL, CryptProtectMemory,
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bool got_crypt(void);
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/*
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* Function to obfuscate an input string into something usable as a
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* pathname for a Windows named pipe. Uses CryptProtectMemory to make
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* the obfuscation depend on a key Windows stores for the owning user,
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* and then hashes the string as well to make it have a manageable
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* length and be composed of filename-legal characters.
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*
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* Rationale: Windows's named pipes all live in the same namespace, so
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* one user can see what pipes another user has open. This is an
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* undesirable privacy leak: in particular, if we used unobfuscated
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* names for the connection-sharing pipe names, it would permit one
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* user to know what username@host another user is SSHing to.
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*
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* The returned string is dynamically allocated.
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*/
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char *capi_obfuscate_string(const char *realname);
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#endif
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@ -16,91 +16,9 @@
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#include "wincapi.h"
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#include "winsecur.h"
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#ifdef COVERITY
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/*
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* The hack I use to build for Coverity scanning, using winegcc and
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* Makefile.mgw, didn't provide some defines in wincrypt.h last time I
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* looked. Therefore, define them myself here, but enclosed in #ifdef
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* COVERITY to ensure I don't make up random nonsense values for any
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* real build.
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*/
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#ifndef CRYPTPROTECTMEMORY_BLOCK_SIZE
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#define CRYPTPROTECTMEMORY_BLOCK_SIZE 16
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#endif
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#ifndef CRYPTPROTECTMEMORY_CROSS_PROCESS
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#define CRYPTPROTECTMEMORY_CROSS_PROCESS 1
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#endif
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#endif
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#define CONNSHARE_PIPE_PREFIX "\\\\.\\pipe\\putty-connshare"
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#define CONNSHARE_MUTEX_PREFIX "Local\\putty-connshare-mutex"
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static char *obfuscate_name(const char *realname)
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{
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/*
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* Windows's named pipes all live in the same namespace, so one
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* user can see what pipes another user has open. This is an
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* undesirable privacy leak and in particular permits one user to
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* know what username@host another user is SSHing to, so we
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* protect that information by using CryptProtectMemory (which
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* uses a key built in to each user's account).
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*/
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char *cryptdata;
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int cryptlen;
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unsigned char digest[32];
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char retbuf[65];
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int i;
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cryptlen = strlen(realname) + 1;
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cryptlen += CRYPTPROTECTMEMORY_BLOCK_SIZE - 1;
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cryptlen /= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptlen *= CRYPTPROTECTMEMORY_BLOCK_SIZE;
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cryptdata = snewn(cryptlen, char);
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memset(cryptdata, 0, cryptlen);
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strcpy(cryptdata, realname);
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/*
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* CRYPTPROTECTMEMORY_CROSS_PROCESS causes CryptProtectMemory to
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* use the same key in all processes with this user id, meaning
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* that the next PuTTY process calling this function with the same
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* input will get the same data.
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*
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* (Contrast with CryptProtectData, which invents a new session
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* key every time since its API permits returning more data than
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* was input, so calling _that_ and hashing the output would not
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* be stable.)
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*
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* We don't worry too much if this doesn't work for some reason.
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* Omitting this step still has _some_ privacy value (in that
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* another user can test-hash things to confirm guesses as to
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* where you might be connecting to, but cannot invert SHA-256 in
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* the absence of any plausible guess). So we don't abort if we
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* can't call CryptProtectMemory at all, or if it fails.
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*/
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if (got_crypt())
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p_CryptProtectMemory(cryptdata, cryptlen,
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CRYPTPROTECTMEMORY_CROSS_PROCESS);
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/*
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* We don't want to give away the length of the hostname either,
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* so having got it back out of CryptProtectMemory we now hash it.
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*/
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hash_simple(&ssh_sha256, make_ptrlen(cryptdata, cryptlen), digest);
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sfree(cryptdata);
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/*
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* Finally, make printable.
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*/
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for (i = 0; i < 32; i++) {
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sprintf(retbuf + 2*i, "%02x", digest[i]);
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/* the last of those will also write the trailing NUL */
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}
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return dupstr(retbuf);
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}
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static char *make_name(const char *prefix, const char *name)
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{
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char *username, *retname;
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@ -130,7 +48,7 @@ int platform_ssh_share(const char *pi_name, Conf *conf,
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* that it also eliminates any characters illegal in Windows pipe
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* names.
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*/
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name = obfuscate_name(pi_name);
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name = capi_obfuscate_string(pi_name);
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if (!name) {
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*logtext = dupprintf("Unable to call CryptProtectMemory: %s",
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win_strerror(GetLastError()));
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