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such: stop writing through a string literal in the -e path #411

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such: stop writing through a string literal in the -e path #411

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e96517d
such: stop writing through a string literal in the -e path
xanimo Aug 6, 2026
1a7ddd5
such: size the -e entropy buffer from ENTROPY_SIZE_STRING_SIZE
xanimo Aug 11, 2026
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15 changes: 14 additions & 1 deletion src/cli/such.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1210,6 +1210,9 @@ int main(int argc, char* argv[])
char* mnemonic_in = 0;
char* pass = 0;
char* entropy = 0;
/* entropy_size points at a literal, so -e needs somewhere writable.
+ 1 for the terminator ENTROPY_SIZE_STRING_SIZE does not include. */
char entropy_size_buf[ENTROPY_SIZE_STRING_SIZE + 1];
char* entropy_size = "256";
MNEMONIC mnemonic = {0};
SEED seed = {0};
Expand Down Expand Up @@ -1252,7 +1255,17 @@ int main(int argc, char* argv[])
return showError("Parameter -e cannot be used with -y");
entropy = optarg;
if (entropy != NULL){
sprintf(entropy_size, "%zu", strlen(entropy) / HEX_CHARS_PER_BYTE * 8);
/* Bound first: unbounded optarg gives four or more
digits and snprintf truncates rather than overflows. */
size_t entropy_hex_len = strlen(entropy);
if (entropy_hex_len > MAX_ENTROPY_STRING_SIZE - 1)
return showError("Parameter -e exceeds the maximum entropy size");

/* sprintf through the "256" literal wrote to read-only
memory and crashed on every use of -e. */
snprintf(entropy_size_buf, sizeof(entropy_size_buf), "%zu",
entropy_hex_len / HEX_CHARS_PER_BYTE * 8);
entropy_size = entropy_size_buf;
}

break;
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