@leroysheep / MovieWebApp / commits / 09d86a3b98

diff: fix out-of-bounds reads and NULL deref in diffstat UTF-8 truncation

f85b49f3d4a (diff: improve scaling of filenames in diffstat to handle UTF-8 chars, 2026-01-16) introduced a loop in show_stats() that calls utf8_width() repeatedly to skip leading characters until the displayed width fits. However, utf8_width() can return problematic values: - For invalid UTF-8 sequences, pick_one_utf8_char() sets the name pointer to NULL and utf8_width() returns 0. Since name_len does not change, the loop iterates once more and pick_one_utf8_char() dereferences the NULL pointer, crashing. - For control characters, utf8_width() returns -1, so name_len grows when it is expected to shrink. This can cause the loop to consume more characters than the string contains, reading past the trailing NUL. By default, fill_print_name() will C-quote filenames which escapes control characters and invalid bytes to printable text. That avoids this bug from being triggered; however, with core.quotePath=false, most characters are no longer escaped (though some control characters still are) and raw bytes can reach this code. Add tests exercising both failure modes with core.quotePath=false and a narrow --stat-name-width to force truncation: one with a bare 0xC0 byte (invalid UTF-8 lead byte, triggers NULL deref) and one with several C1 control characters (repeats of 0xC2 0x9F, causing the loop to read past the end of the string). The second test reliably catches the out-of-bounds read when run under ASan, though it may pass silently without sanitizers. Fix both issues by introducing utf8_ish_width(), a thin wrapper around utf8_width() that guarantees the pointer always advances and the returned width is never negative: - On invalid UTF-8 it restores the pointer, advances by one byte, and returns width 1 (matching the strlen()-based fallback used by utf8_strwidth()). - On a control character it returns 0 (matching utf8_strnwidth() which skips them). Also add a "&& *name" guard to the while-loop condition so it terminates at end-of-string even when utf8_strwidth()'s strlen() fallback causes name_len to exceed the sum of per-character widths. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Elijah Newren committed Apr 20, 2026 at 15:42 UTC 09d86a3b98573cba6d7c813ec97eadb69e3e2dfd

2 files changed +49 -2

diff.c

+24 -2

index 397e38b41c..1a3b19f71f 100644 --- a/diff.c +++ b/diff.c @@ -2927,6 +2927,28 @@ void print_stat_summary(FILE *fp, int files, print_stat_summary_inserts_deletes(&o, files, insertions, deletions); } +/* + * Like utf8_width(), but guaranteed safe for use in loops that subtract + * per-character widths: + * + * - utf8_width() sets *start to NULL on invalid UTF-8 and returns 0; + * we restore the pointer and advance by one byte, returning width 1 + * (matching the strlen()-based fallback in utf8_strwidth()). + * + * - utf8_width() returns -1 for control characters; we return 0 + * (matching utf8_strnwidth() which skips them). + */ +static int utf8_ish_width(const char **start) +{ + const char *old = *start; + int w = utf8_width(start, NULL); + if (!*start) { + *start = old + 1; + return 1; + } + return (w < 0) ? 0 : w; +} + static void show_stats(struct diffstat_t *data, struct diff_options *options) { int i, len, add, del, adds = 0, dels = 0; @@ -3093,8 +3115,8 @@ static void show_stats(struct diffstat_t *data, struct diff_options *options) if (len < 0) len = 0; - while (name_len > len) - name_len -= utf8_width((const char**)&name, NULL); + while (name_len > len && *name) + name_len -= utf8_ish_width((const char**)&name); slash = strchr(name, '/'); if (slash)

t/t4052-stat-output.sh

+25

index 7c749062e2..e009585925 100755 --- a/t/t4052-stat-output.sh +++ b/t/t4052-stat-output.sh @@ -445,4 +445,29 @@ test_expect_success 'diffstat where line_prefix contains ANSI escape codes is co test_grep "<RED>|<RESET> ${FILENAME_TRIMMED} | 0" out ' +test_expect_success 'diffstat truncation with invalid UTF-8 does not crash' ' + empty_blob=$(git hash-object -w --stdin </dev/null) && + printf "100644 blob $empty_blob\taaa-\300-aaa\n" | + git mktree >tree_file && + tree=$(cat tree_file) && + empty_tree=$(git mktree </dev/null) && + c1=$(git commit-tree -m before $empty_tree) && + c2=$(git commit-tree -m after -p $c1 $tree) && + git -c core.quotepath=false diff --stat --stat-name-width=5 $c1..$c2 >output && + test_grep "| 0" output +' + +test_expect_success FUNNYNAMES 'diffstat truncation with control chars does not read out of bounds' ' + FNAME=$(printf "aaa-\302\237\302\237\302\237-aaa") && + git commit --allow-empty -m setup && + >$FNAME && + git add -- $FNAME && + git commit -m "add file with control char name" && + git -c core.quotepath=false diff --stat --stat-name-width=5 HEAD~1..HEAD >output && + test_grep "| 0" output && + rm -- $FNAME && + git rm -- $FNAME && + git commit -m "remove test file" +' + test_done