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py/formatfloat: Fix buffer overflow when formatting tiny numbers.

This commit is contained in:
Damien George 2016-03-15 12:21:56 +00:00
parent 0d1f8868b6
commit cea6cf8a5e
2 changed files with 26 additions and 4 deletions
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14
py/formatfloat.c
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@ -27,6 +27,7 @@
#include "py/mpconfig.h"
#if MICROPY_FLOAT_IMPL != MICROPY_FLOAT_IMPL_NONE
#include <assert.h>
#include <stdlib.h>
#include <stdint.h>
#include "py/formatfloat.h"
@ -210,13 +211,15 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
dec = -1;
*s++ = first_dig;
if (prec + e + 1 > buf_remaining) {
prec = buf_remaining - e - 1;
}
if (org_fmt == 'g') {
prec += (e - 1);
}
// truncate precision to prevent buffer overflow
if (prec + 2 > buf_remaining) {
prec = buf_remaining - 2;
}
num_digits = prec;
if (num_digits) {
*s++ = '.';
@ -390,6 +393,9 @@ int mp_format_float(FPTYPE f, char *buf, size_t buf_size, char fmt, int prec, ch
}
*s = '\0';
// verify that we did not overrun the input buffer
assert((size_t)(s + 1 - buf) <= buf_size);
return s - buf;
}

16
tests/float/string_format_modulo.py
View File

@ -26,3 +26,19 @@ print("%02.3d" % 123) # prec > width
print("%+f %+f" % (1.23, -1.23)) # float sign
print("% f % f" % (1.23, -1.23)) # float space sign
print("%0f" % -1.23) # negative number with 0 padding
# numbers with large negative exponents
print('%f' % 1e-10)
print('%f' % 1e-20)
print('%f' % 1e-50)
print('%f' % 1e-100)
print('%f' % 1e-300)
# large decimal precision should be truncated and not overflow buffer
# the output depends on the FP calculation so only first 2 digits are printed
# (the 'g' with small e are printed using 'f' style, so need to be checked)
print(('%.40f' % 1e-300)[:2])
print(('%.40g' % 1e-1)[:2])
print(('%.40g' % 1e-2)[:2])
print(('%.40g' % 1e-3)[:2])
print(('%.40g' % 1e-4)[:2])