[hackers] [libgrapheme] Properly return offset when input is shorter or equal to one codepoint || Laslo Hunhold

From: <git_AT_suckless.org>
Date: Sun, 21 Aug 2022 13:51:44 +0200 (CEST)

commit c8715cbecccbdb61b2f46f7ad18e015ba8703637
Author: Laslo Hunhold <dev_AT_frign.de>
AuthorDate: Sun Aug 21 13:47:19 2022 +0200
Commit: Laslo Hunhold <dev_AT_frign.de>
CommitDate: Sun Aug 21 13:51:22 2022 +0200

    Properly return offset when input is shorter or equal to one codepoint
    
    I sadly didn't catch this bug with automatic testing, given I didn't
    cover the shorthand-check at the beginning of the breakpoint-detection
    functions in any test-case. Additionally, it would be shadowed when
    simply working with UCS-4-arrays.
    
    On a higher level, this surfaced when checking the title-case of
    one-character-strings, given it would first get the next word-break
    (which would be underreported as 1 instead of something >1) only to
    subtract the real offset of the grapheme-cluster-bytelen later on,
    leading to an underflow and infinite loop.
    
    Thanks to polarisFuton9719 for reporting this bug!
    
    Signed-off-by: Laslo Hunhold <dev_AT_frign.de>

diff --git a/src/case.c b/src/case.c
index 21ec5af..1be387d 100644
--- a/src/case.c
+++ b/src/case.c
_AT_@ -431,9 +431,13 @@ is_titlecase(const void *src, size_t srclen,
                                 }
                         }
 
- /* we consumed a character */
+ /*
+ * we consumed a character (make sure to never
+ * underflow next_wb; this should not happen,
+ * but it's better to be sure)
+ */
                         srcoff += res;
- next_wb -= res;
+ next_wb -= (res <= next_wb) ? res : next_wb;
                 }
 
                 /* check if the rest of the codepoints in the word are lowercase */
diff --git a/src/line.c b/src/line.c
index bced2f2..051e152 100644
--- a/src/line.c
+++ b/src/line.c
_AT_@ -51,7 +51,11 @@ next_line_break(const void *str, size_t len, size_t (*get_codepoint)
          */
         cp0_prop = NUM_LINE_BREAK_PROPS;
         if ((off = get_codepoint(str, len, 0, &cp)) >= len) {
- return 1;
+ /*
+ * A line is at least one codepoint long, so we can
+ * safely return here
+ */
+ return len;
         }
         cp1_prop = get_break_prop(cp);
         last_non_cm_or_zwj_prop = LINE_BREAK_PROP_AL; /* according to LB10 */
diff --git a/src/sentence.c b/src/sentence.c
index a5850ec..d464edc 100644
--- a/src/sentence.c
+++ b/src/sentence.c
_AT_@ -66,7 +66,11 @@ next_sentence_break(const void *str, size_t len, size_t (*get_codepoint)
          */
         raw.b = NUM_SENTENCE_BREAK_PROPS;
         if ((off = get_codepoint(str, len, 0, &cp)) >= len) {
- return 1;
+ /*
+ * A line is at least one codepoint long, so we can
+ * safely return here
+ */
+ return len;
         }
         raw.c = get_break_prop(cp);
         (void)get_codepoint(str, len, off, &cp);
diff --git a/src/word.c b/src/word.c
index e8e9b44..dffb5b5 100644
--- a/src/word.c
+++ b/src/word.c
_AT_@ -64,7 +64,11 @@ next_word_break(const void *str, size_t len, size_t (*get_codepoint)
          */
         raw.b = NUM_WORD_BREAK_PROPS;
         if ((off = get_codepoint(str, len, 0, &cp)) >= len) {
- return 1;
+ /*
+ * A line is at least one codepoint long, so we can
+ * safely return here
+ */
+ return len;
         }
         raw.c = get_break_prop(cp);
         (void)get_codepoint(str, len, off, &cp);
Received on Sun Aug 21 2022 - 13:51:44 CEST