Protect against small overread in SASLprep validation

(This is a cherry-pick of 390b3cbbb, which I hadn't realized wasn't
backpatched. It was originally reported to security@ and determined not
to be a vulnerability; thanks to Stanislav Osipov for noticing the
omission in the back branches.)

In case of torn UTF8 in the input data we might end up going
past the end of the string since we don't account for length.
While validation won't be performed on a sequence with a NULL
byte it's better to avoid going past the end to beging with.
Fix by taking the length into consideration.

Reported-by: Stanislav Osipov <stasos24@gmail.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CAOYmi+mTnmM172g=_+Yvc47hzzeAsYPy2C4UBY3HK9p-AXNV0g@mail.gmail.com
Backpatch-through: 14

diff --git a/src/common/saslprep.c b/src/common/saslprep.c
index 792957bd27555fd16bdbfb4475a25522b33e2900..0a840352802e04945202af62f5d3be20a25f569a 100644 (file)
--- a/src/common/saslprep.c
+++ b/src/common/saslprep.c
@@ -1009,15 +1009,17 @@ pg_utf8_string_len(const char *source)
        const unsigned char *p = (const unsigned char *) source;
        int                     l;
        int                     num_chars = 0;
+       size_t          len = strlen(source);
 
-       while (*p)
+       while (len)
        {
                l = pg_utf_mblen(p);
 
-               if (!pg_utf8_islegal(p, l))
+               if (len < l || !pg_utf8_islegal(p, l))
                        return -1;
 
                p += l;
+               len -= l;
                num_chars++;
        }