Originally, the only OpenSSL API to stringify errors was:
char *ERR_error_string(unsigned long e, char *buf);
This API leaves callers a choice to either be thread unsafe (buf = NULL)
or pass in a buffer with unknown size. Indeed the original
implementation was just a bunch of unchecked sprintfs with, in the buf =
NULL case, a static 256-byte buffer.
388f2f56f2/crypto/err/err.c (L374)
Then ERR_error_string was documented that the buffer must be size 120.
Nowhere in the code was 120 significant. I expect OpenSSL just made up a
number.
388f2f56f2
Then upstream added the ERR_error_string_n API. Although the
documentation stated 120 bytes, the internal buffer was 256, so the code
actually translates ERR_error_string to ERR_error_string_n(e, buf, 256),
not ERR_error_string_n(e, buf, 120)!
e5c84d5152
So the documentation was wrong all this time! OpenSSL 1.1.0 corrected
the documentation to 256, but, alas, a lot of code used the
documentation and sized the buffer at 120. We should fix all
ERR_error_string callers to ERR_error_string_n but, in the meantime,
using 120 is probably less effort.
Note this also affects ERR_print_errors_cb right now. We don't have
function codes, so 120 bytes leaves 60 bytes for the reason code. Our
longest one, TLS_PEER_DID_NOT_RESPOND_WITH_CERTIFICATE_LIST is 46 bytes,
so it's a little tight, but, if needed, we can recover 20-ish bytes by
shrinking the library names. We can also always make ERR_print_errors_cb
use a larger buffer.
Change-Id: I472a1a802f2e6281cc7515d2a452208d6bac1200
Reviewed-on: https://boringssl-review.googlesource.com/24184
Reviewed-by: Adam Langley <agl@google.com>