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secp256k1
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Return NULL early in context_preallocated_create if flags invalid 

If the user passes invalid flags to _context_create, and the default
illegal callback does not abort the program (which is possible), then we
work with the result of malloc(0), which may be undefined behavior. This
violates the promise that a library function won't crash after the
illegal callback has been called.

This commit fixes this issue by returning NULL early in _context_create
in that case.
This commit is contained in:
Tim Ruffing 2020-10-26 14:38:30 +01:00
parent ac05f61fcf
commit ebfa2058e9
1 changed files with 9 additions and 7 deletions
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16
src/secp256k1.c
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@ -86,6 +86,8 @@ const secp256k1_context *secp256k1_context_no_precomp = &secp256k1_context_no_pr
size_t secp256k1_context_preallocated_size(unsigned int flags) {
size_t ret = ROUND_TO_ALIGN(sizeof(secp256k1_context));
/* A return value of 0 is reserved as an indicator for errors when we call this function internally. */
VERIFY_CHECK(ret != 0);
if (EXPECT((flags & SECP256K1_FLAGS_TYPE_MASK) != SECP256K1_FLAGS_TYPE_CONTEXT, 0)) {
secp256k1_callback_call(&default_illegal_callback,
@ -122,21 +124,21 @@ secp256k1_context* secp256k1_context_preallocated_create(void* prealloc, unsigne
if (!secp256k1_selftest()) {
secp256k1_callback_call(&default_error_callback, "self test failed");
}
VERIFY_CHECK(prealloc != NULL);
prealloc_size = secp256k1_context_preallocated_size(flags);
if (prealloc_size == 0) {
return NULL;
}
VERIFY_CHECK(prealloc != NULL);
ret = (secp256k1_context*)manual_alloc(&prealloc, sizeof(secp256k1_context), base, prealloc_size);
ret->illegal_callback = default_illegal_callback;
ret->error_callback = default_error_callback;
if (EXPECT((flags & SECP256K1_FLAGS_TYPE_MASK) != SECP256K1_FLAGS_TYPE_CONTEXT, 0)) {
secp256k1_callback_call(&ret->illegal_callback,
"Invalid flags");
return NULL;
}
secp256k1_ecmult_context_init(&ret->ecmult_ctx);
secp256k1_ecmult_gen_context_init(&ret->ecmult_gen_ctx);
/* Flags have been checked by secp256k1_context_preallocated_size. */
VERIFY_CHECK((flags & SECP256K1_FLAGS_TYPE_MASK) == SECP256K1_FLAGS_TYPE_CONTEXT);
if (flags & SECP256K1_FLAGS_BIT_CONTEXT_SIGN) {
secp256k1_ecmult_gen_context_build(&ret->ecmult_gen_ctx, &prealloc);
}