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src/common.c: Fix heap buffer overflows when writing strings in binhe…
…ader Fixes the following problems: 1. Case 's' only enlarges the buffer by 16 bytes instead of size bytes. 2. psf_binheader_writef() enlarges the header buffer (if needed) prior to the big switch statement by an amount (16 bytes) which is enough for all cases where only a single value gets added. Cases 's', 'S', 'p' however additionally write an arbitrary length block of data and again enlarge the buffer to the required amount. However, the required space calculation does not take into account the size of the length field which gets output before the data. 3. Buffer size requirement calculation in case 'S' does not account for the padding byte ("size += (size & 1) ;" happens after the calculation which uses "size"). 4. Case 'S' can overrun the header buffer by 1 byte when no padding is involved ("memcpy (&(psf->header.ptr [psf->header.indx]), strptr, size + 1) ;" while the buffer is only guaranteed to have "size" space available). 5. "psf->header.ptr [psf->header.indx] = 0 ;" in case 'S' always writes 1 byte beyond the space which is guaranteed to be allocated in the header buffer. 6. Case 's' can overrun the provided source string by 1 byte if padding is involved ("memcpy (&(psf->header.ptr [psf->header.indx]), strptr, size) ;" where "size" is "strlen (strptr) + 1" (which includes the 0 terminator, plus optionally another 1 which is padding and not guaranteed to be readable via the source string pointer). Closes: libsndfile#292
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