Fix int truncation of read length in shmop_read()#22425
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shmop_read() held the read length in an int while count and shmop->size are zend_long and the bounds checks above validate against the full 64-bit size. On a shared-memory segment larger than INT_MAX a read whose length sets the int sign bit was sign-extended into the size_t length argument of zend_string_init(), requesting a near-SIZE_MAX allocation; other truncated lengths silently returned a wrong-sized string. Hold the length in a zend_long, matching the zend_long writesize already used in shmop_write().
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Looks good but I am not an expert in this. cc @Girgias if she might offer some help :) |
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shmop_read() held the read length in an int while count and shmop->size are zend_long and the bounds checks validate against the full 64-bit size. On a shared-memory segment larger than INT_MAX, a length that sets the int sign bit was sign-extended into the size_t argument of zend_string_init(), requesting a near-SIZE_MAX allocation; other truncated lengths returned a wrong-sized string. Hold the length in a zend_long, matching the zend_long writesize already used in shmop_write(). Triggering needs a >2GB segment, so there is no portable red/green test; the fix is a type correction with no behavioral change below INT_MAX.