libcrypto bio_cb.c: fix mangled debug output

[Martin Vahlensieck]

Hi

This fixes mangled output from the openssl(1) -debug option:

Before:
$ openssl aes-256-cbc -out test -debug
BIO[0x9102a7e5ctrl(106) - FILE pointer
BIO[0x9102a7e5ctrl return 1
BIO[0x9102a801ctrl(108) - FILE pointer
BIO[0x9102a801ctrl return 1
...

After:
$ openssl aes-256-cbc -out test -debug
BIO[0x5770f81ce00]:ctrl(106) - FILE pointer
BIO[0x5770f81ce00]:ctrl return 1
BIO[0x5770f81c200]:ctrl(108) - FILE pointer
BIO[0x5770f81c200]:ctrl return 1
BIO[0x5770f81c200]:write(0,8) - FILE pointer
...

The issue is that BIO_debug_callback(3) assumes that the pointer
formatted with %p takes up 6 chars.

Best,

Martin

Index: bio/bio_cb.c
===================================================================
RCS file: /cvs/src/lib/libcrypto/bio/bio_cb.c,v
retrieving revision 1.16
diff -u -p -r1.16 bio_cb.c
--- bio/bio_cb.c        8 Dec 2014 03:54:19 -0000       1.16
+++ bio/bio_cb.c        24 Mar 2021 09:50:45 -0000
@@ -70,15 +70,20 @@ BIO_debug_callback(BIO *bio, int cmd, co
        BIO *b;
        char buf[256];
        char *p;
+       int nbuf;
        long r = 1;
        size_t p_maxlen;
 
        if (BIO_CB_RETURN & cmd)
                r = ret;
 
-       snprintf(buf, sizeof buf, "BIO[%p]:", bio);
-       p = &(buf[14]);
-       p_maxlen = sizeof buf - 14;
+       nbuf = snprintf(buf, sizeof buf, "BIO[%p]:", bio);
+
+       if (nbuf > sizeof buf)
+               nbuf = sizeof buf;
+
+       p = &(buf[nbuf]);
+       p_maxlen = sizeof buf - nbuf;
        switch (cmd) {
        case BIO_CB_FREE:
                snprintf(p, p_maxlen, "Free - %s\n", bio->method->name);