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Rewrite BN_CTX.

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While allocating near INT_MAX BIGNUMs or stack frames would never happen, we
should properly handle overflow here. Rewrite it to just be a STACK_OF(BIGNUM)
plus a stack of indices. Also simplify the error-handling. If we make the
errors truly sticky (rather than just sticky per frame), we don't need to keep
track of err_stack and friends.

Thanks to mlbrown for reporting the integer overflows in the original
implementation.

Bug: chromium:942269
Change-Id: Ie9c9baea3eeb82d65d88b1cb1388861f5cd84fe5
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/35328
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2019-03-14 19:25:41 -05:00 committed by CQ bot account: commit-bot@chromium.org
parent c93be52c9e
commit 4ca8d131d3
1 changed files with 89 additions and 160 deletions
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249
crypto/fipsmodule/bn/ctx.c
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@ -54,6 +54,7 @@
#include <openssl/bn.h> #include <openssl/bn.h>
#include <assert.h>
#include <string.h> #include <string.h>
#include <openssl/err.h> #include <openssl/err.h>
@ -62,63 +63,46 @@
#include "../../internal.h" #include "../../internal.h"
// How many bignums are in each "pool item";
#define BN_CTX_POOL_SIZE 16
// The stack frame info is resizing, set a first-time expansion size; // The stack frame info is resizing, set a first-time expansion size;
#define BN_CTX_START_FRAMES 32 #define BN_CTX_START_FRAMES 32
// A bundle of bignums that can be linked with other bundles
typedef struct bignum_pool_item {
// The bignum values
BIGNUM vals[BN_CTX_POOL_SIZE];
// Linked-list admin
struct bignum_pool_item *prev, *next;
} BN_POOL_ITEM;
typedef struct bignum_pool {
// Linked-list admin
BN_POOL_ITEM *head, *current, *tail;
// Stack depth and allocation size
unsigned used, size;
} BN_POOL;
static void BN_POOL_init(BN_POOL *);
static void BN_POOL_finish(BN_POOL *);
static BIGNUM *BN_POOL_get(BN_POOL *);
static void BN_POOL_release(BN_POOL *, unsigned int);
// BN_STACK // BN_STACK
// A wrapper to manage the "stack frames" // A |BN_STACK| is a stack of |size_t| values.
typedef struct bignum_ctx_stack { typedef struct {
// Array of indexes into the bignum stack // Array of indexes into |ctx->bignums|.
unsigned int *indexes; size_t *indexes;
// Number of stack frames, and the size of the allocated array // Number of stack frames, and the size of the allocated array
unsigned int depth, size; size_t depth, size;
} BN_STACK; } BN_STACK;
static void BN_STACK_init(BN_STACK *); static void BN_STACK_init(BN_STACK *);
static void BN_STACK_finish(BN_STACK *); static void BN_STACK_cleanup(BN_STACK *);
static int BN_STACK_push(BN_STACK *, unsigned int); static int BN_STACK_push(BN_STACK *, size_t idx);
static unsigned int BN_STACK_pop(BN_STACK *); static size_t BN_STACK_pop(BN_STACK *);
// BN_CTX // BN_CTX
DEFINE_STACK_OF(BIGNUM)
// The opaque BN_CTX type // The opaque BN_CTX type
struct bignum_ctx { struct bignum_ctx {
// The bignum bundles // bignums is the stack of |BIGNUM|s managed by this |BN_CTX|.
BN_POOL pool; STACK_OF(BIGNUM) *bignums;
// The "stack frames", if you will // stack is the stack of |BN_CTX_start| frames. It is the value of |used| at
// the time |BN_CTX_start| was called.
BN_STACK stack; BN_STACK stack;
// The number of bignums currently assigned // used is the number of |BIGNUM|s from |bignums| that have been used.
unsigned int used; size_t used;
// Depth of stack overflow // error is one if any operation on this |BN_CTX| failed. All subsequent
int err_stack; // operations will fail.
// Block "gets" until an "end" (compatibility behaviour) char error;
int too_many; // defer_error is one if an operation on this |BN_CTX| has failed, but no
// error has been pushed to the queue yet. This is used to defer errors from
// |BN_CTX_start| to |BN_CTX_get|.
char defer_error;
}; };
BN_CTX *BN_CTX_new(void) { BN_CTX *BN_CTX_new(void) {
@ -129,11 +113,11 @@ BN_CTX *BN_CTX_new(void) {
} }
// Initialise the structure // Initialise the structure
BN_POOL_init(&ret->pool); ret->bignums = NULL;
BN_STACK_init(&ret->stack); BN_STACK_init(&ret->stack);
ret->used = 0; ret->used = 0;
ret->err_stack = 0; ret->error = 0;
ret->too_many = 0; ret->defer_error = 0;
return ret; return ret;
} }
@ -142,57 +126,69 @@ void BN_CTX_free(BN_CTX *ctx) {
return; return;
} }
BN_STACK_finish(&ctx->stack); sk_BIGNUM_pop_free(ctx->bignums, BN_free);
BN_POOL_finish(&ctx->pool); BN_STACK_cleanup(&ctx->stack);
OPENSSL_free(ctx); OPENSSL_free(ctx);
} }
void BN_CTX_start(BN_CTX *ctx) { void BN_CTX_start(BN_CTX *ctx) {
// If we're already overflowing ... if (ctx->error) {
if (ctx->err_stack || ctx->too_many) { // Once an operation has failed, |ctx->stack| no longer matches the number
ctx->err_stack++; // of |BN_CTX_end| calls to come. Do nothing.
} else if (!BN_STACK_push(&ctx->stack, ctx->used)) { return;
// (Try to) get a new frame pointer }
OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
ctx->err_stack++; if (!BN_STACK_push(&ctx->stack, ctx->used)) {
ctx->error = 1;
// |BN_CTX_start| cannot fail, so defer the error to |BN_CTX_get|.
ctx->defer_error = 1;
} }
} }
BIGNUM *BN_CTX_get(BN_CTX *ctx) { BIGNUM *BN_CTX_get(BN_CTX *ctx) {
BIGNUM *ret; // Once any operation has failed, they all do.
if (ctx->err_stack || ctx->too_many) { if (ctx->error) {
if (ctx->defer_error) {
OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
ctx->defer_error = 0;
}
return NULL; return NULL;
} }
ret = BN_POOL_get(&ctx->pool); if (ctx->bignums == NULL) {
if (ret == NULL) { ctx->bignums = sk_BIGNUM_new_null();
// Setting too_many prevents repeated "get" attempts from if (ctx->bignums == NULL) {
// cluttering the error stack. OPENSSL_PUT_ERROR(BN, ERR_R_MALLOC_FAILURE);
ctx->too_many = 1; ctx->error = 1;
OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES); return NULL;
return NULL; }
} }
// OK, make sure the returned bignum is "zero" if (ctx->used == sk_BIGNUM_num(ctx->bignums)) {
BIGNUM *bn = BN_new();
if (bn == NULL || !sk_BIGNUM_push(ctx->bignums, bn)) {
OPENSSL_PUT_ERROR(BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
BN_free(bn);
ctx->error = 1;
return NULL;
}
}
BIGNUM *ret = sk_BIGNUM_value(ctx->bignums, ctx->used);
BN_zero(ret); BN_zero(ret);
// This is bounded by |sk_BIGNUM_num|, so it cannot overflow.
ctx->used++; ctx->used++;
return ret; return ret;
} }
void BN_CTX_end(BN_CTX *ctx) { void BN_CTX_end(BN_CTX *ctx) {
if (ctx->err_stack) { if (ctx->error) {
ctx->err_stack--; // Once an operation has failed, |ctx->stack| no longer matches the number
} else { // of |BN_CTX_end| calls to come. Do nothing.
unsigned int fp = BN_STACK_pop(&ctx->stack); return;
// Does this stack frame have anything to release?
if (fp < ctx->used) {
BN_POOL_release(&ctx->pool, ctx->used - fp);
}
ctx->used = fp;
// Unjam "too_many" in case "get" had failed
ctx->too_many = 0;
} }
ctx->used = BN_STACK_pop(&ctx->stack);
} }
@ -203,101 +199,34 @@ static void BN_STACK_init(BN_STACK *st) {
st->depth = st->size = 0; st->depth = st->size = 0;
} }
static void BN_STACK_finish(BN_STACK *st) { static void BN_STACK_cleanup(BN_STACK *st) {
OPENSSL_free(st->indexes); OPENSSL_free(st->indexes);
} }
static int BN_STACK_push(BN_STACK *st, unsigned int idx) { static int BN_STACK_push(BN_STACK *st, size_t idx) {
if (st->depth == st->size) { if (st->depth == st->size) {
// Need to expand // This function intentionally does not push to the error queue on error.
unsigned int newsize = // Error-reporting is deferred to |BN_CTX_get|.
(st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES); size_t new_size = st->size != 0 ? st->size * 3 / 2 : BN_CTX_START_FRAMES;
unsigned int *newitems = OPENSSL_malloc(newsize * sizeof(unsigned int)); if (new_size <= st->size || new_size > ((size_t)-1) / sizeof(size_t)) {
if (!newitems) {
return 0; return 0;
} }
if (st->depth) { size_t *new_indexes =
OPENSSL_memcpy(newitems, st->indexes, st->depth * sizeof(unsigned int)); OPENSSL_realloc(st->indexes, new_size * sizeof(size_t));
if (new_indexes == NULL) {
return 0;
} }
OPENSSL_free(st->indexes); st->indexes = new_indexes;
st->indexes = newitems; st->size = new_size;
st->size = newsize;
} }
st->indexes[(st->depth)++] = idx; st->indexes[st->depth] = idx;
st->depth++;
return 1; return 1;
} }
static unsigned int BN_STACK_pop(BN_STACK *st) { static size_t BN_STACK_pop(BN_STACK *st) {
return st->indexes[--(st->depth)]; assert(st->depth > 0);
} st->depth--;
return st->indexes[st->depth];
static void BN_POOL_init(BN_POOL *p) {
p->head = p->current = p->tail = NULL;
p->used = p->size = 0;
}
static void BN_POOL_finish(BN_POOL *p) {
while (p->head) {
for (size_t i = 0; i < BN_CTX_POOL_SIZE; i++) {
BN_clear_free(&p->head->vals[i]);
}
p->current = p->head->next;
OPENSSL_free(p->head);
p->head = p->current;
}
}
static BIGNUM *BN_POOL_get(BN_POOL *p) {
if (p->used == p->size) {
BN_POOL_ITEM *item = OPENSSL_malloc(sizeof(BN_POOL_ITEM));
if (!item) {
return NULL;
}
// Initialise the structure
for (size_t i = 0; i < BN_CTX_POOL_SIZE; i++) {
BN_init(&item->vals[i]);
}
item->prev = p->tail;
item->next = NULL;
// Link it in
if (!p->head) {
p->head = p->current = p->tail = item;
} else {
p->tail->next = item;
p->tail = item;
p->current = item;
}
p->size += BN_CTX_POOL_SIZE;
p->used++;
// Return the first bignum from the new pool
return item->vals;
}
if (!p->used) {
p->current = p->head;
} else if ((p->used % BN_CTX_POOL_SIZE) == 0) {
p->current = p->current->next;
}
return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
}
static void BN_POOL_release(BN_POOL *p, unsigned int num) {
unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
p->used -= num;
while (num--) {
if (!offset) {
offset = BN_CTX_POOL_SIZE - 1;
p->current = p->current->prev;
} else {
offset--;
}
}
} }