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 3dddb924088a49436f124ec3a04b8773c5db97a4..b8fe2026f99a1fbd708051b6244450c3e93b9c01 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++;
        }