From 377c25d32275a65043f9dcf3d4668a56c37319e2 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Thu, 9 May 2024 12:45:51 +0900 Subject: [PATCH] Fix overread in JSON parsing errors for incomplete byte sequences json_lex_string() relies on pg_encoding_mblen_bounded() to point to the end of a JSON string when generating an error message, and the input it uses is not guaranteed to be null-terminated. It was possible to walk off the end of the input buffer by a few bytes when the last bytes consist of an incomplete multi-byte sequence, as token_terminator would point to a location defined by pg_encoding_mblen_bounded() rather than the end of the input. This commit switches token_terminator so as the error uses data up to the end of the JSON input. More work should be done so as this code could rely on an equivalent of report_invalid_encoding() so as incorrect byte sequences can show in error messages in a readable form. This requires work for at least two cases in the JSON parsing API: an incomplete token and an invalid escape sequence. A more complete solution may be too invasive for a backpatch, so this is left as a future improvement, taking care of the overread first. A test is added on HEAD as test_json_parser makes this issue straight-forward to check. Note that pg_encoding_mblen_bounded() no longer has any callers. This will be removed on HEAD with a separate commit, as this is proving to encourage unsafe coding. Author: Jacob Champion Discussion: https://postgr.es/m/CAOYmi+ncM7pwLS3AnKCSmoqqtpjvA8wmCdoBtKA3ZrB2hZG6zA@mail.gmail.com Backpatch-through: 13 --- src/common/jsonapi.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/src/common/jsonapi.c b/src/common/jsonapi.c index 177f6e7d95..74df1dc5a3 100644 --- a/src/common/jsonapi.c +++ b/src/common/jsonapi.c @@ -686,6 +686,7 @@ static inline JsonParseErrorType json_lex_string(JsonLexContext *lex) { char *s; + char *const end = lex->input + lex->input_length; int len; int hi_surrogate = -1; @@ -697,8 +698,8 @@ json_lex_string(JsonLexContext *lex) } while (0) #define FAIL_AT_CHAR_END(code) \ do { \ - lex->token_terminator = \ - s + pg_encoding_mblen_bounded(lex->input_encoding, s); \ + char *term = s + pg_encoding_mblen(lex->input_encoding, s); \ + lex->token_terminator = (term <= end) ? term : end; \ return code; \ } while (0)