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rand: Fix a bug acquiring a context on windows

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The details can be found in the comment I wrote on the block in question, but
the gist of it is that our usage of the TIB for a stack limit was causing
CryptAcquireContext to fail, so we temporarily get around it by setting the
stack limit to 0.
This commit is contained in:
Alex Crichton 2014-03-21 11:51:11 -07:00
parent d2e99a0b33
commit e7c4fb692b
1 changed files with 39 additions and 1 deletions
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40
src/librand/os.rs
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@ -63,6 +63,7 @@ mod imp {
use std::cast;
use std::libc::{c_ulong, DWORD, BYTE, LPCSTR, BOOL};
use std::os;
use std::rt::stack;
type HCRYPTPROV = c_ulong;
@ -82,6 +83,7 @@ mod imp {
static PROV_RSA_FULL: DWORD = 1;
static CRYPT_SILENT: DWORD = 64;
static CRYPT_VERIFYCONTEXT: DWORD = 0xF0000000;
static NTE_BAD_SIGNATURE: DWORD = 0x80090006;
extern "system" {
fn CryptAcquireContextA(phProv: *mut HCRYPTPROV,
@ -99,11 +101,47 @@ mod imp {
/// Create a new `OSRng`.
pub fn new() -> OSRng {
let mut hcp = 0;
let ret = unsafe {
let mut ret = unsafe {
CryptAcquireContextA(&mut hcp, 0 as LPCSTR, 0 as LPCSTR,
PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_SILENT)
};
// It turns out that if we can't acquire a context with the
// NTE_BAD_SIGNATURE error code, the documentation states:
//
// The provider DLL signature could not be verified. Either the
// DLL or the digital signature has been tampered with.
//
// Sounds fishy, no? As it turns out, our signature can be bad
// because our Thread Information Block (TIB) isn't exactly what it
// expects. As to why, I have no idea. The only data we store in the
// TIB is the stack limit for each thread, but apparently that's
// enough to make the signature valid.
//
// Furthermore, this error only happens the *first* time we call
// CryptAcquireContext, so we don't have to worry about future
// calls.
//
// Anyway, the fix employed here is that if we see this error, we
// pray that we're not close to the end of the stack, temporarily
// set the stack limit to 0 (what the TIB originally was), acquire a
// context, and then reset the stack limit.
//
// Again, I'm not sure why this is the fix, nor why we're getting
// this error. All I can say is that this seems to allow libnative
// to progress where it otherwise would be hindered. Who knew?
if ret == 0 && os::errno() as DWORD == NTE_BAD_SIGNATURE {
unsafe {
let limit = stack::get_sp_limit();
stack::record_sp_limit(0);
ret = CryptAcquireContextA(&mut hcp, 0 as LPCSTR, 0 as LPCSTR,
PROV_RSA_FULL,
CRYPT_VERIFYCONTEXT | CRYPT_SILENT);
stack::record_sp_limit(limit);
}
}
if ret == 0 {
fail!("couldn't create context: {}", os::last_os_error());
}