pretty: fix integer overflow in wrapping format

The `%w(width,indent1,indent2)` formatting directive can be used to
rewrap text to a specific width and is designed after git-shortlog(1)'s
`-w` parameter. While the three parameters are all stored as `size_t`
internally, `strbuf_add_wrapped_text()` accepts integers as input. As a
result, the casted integers may overflow. As these now-negative integers
are later on passed to `strbuf_addchars()`, we will ultimately run into
implementation-defined behaviour due to casting a negative number back
to `size_t` again. On my platform, this results in trying to allocate
9000 petabyte of memory.

Fix this overflow by using `cast_size_t_to_int()` so that we reject
inputs that cannot be represented as an integer.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

git-compat-util.h

@@ -918,6 +918,14 @@ static inline size_t st_sub(size_t a, size_t b)
 	return a - b;
 }
 
+static inline int cast_size_t_to_int(size_t a)
+{
+	if (a > INT_MAX)
+		die("number too large to represent as int on this platform: %"PRIuMAX,
+		    (uintmax_t)a);
+	return (int)a;
+}
+
 #ifdef HAVE_ALLOCA_H
 # include <alloca.h>
 # define xalloca(size)      (alloca(size))

pretty.c

@@ -915,7 +915,9 @@ static void strbuf_wrap(struct strbuf *sb, size_t pos,
 	if (pos)
 		strbuf_add(&tmp, sb->buf, pos);
 	strbuf_add_wrapped_text(&tmp, sb->buf + pos,
-				(int) indent1, (int) indent2, (int) width);
+				cast_size_t_to_int(indent1),
+				cast_size_t_to_int(indent2),
+				cast_size_t_to_int(width));
 	strbuf_swap(&tmp, sb);
 	strbuf_release(&tmp);
 }

t/t4205-log-pretty-formats.sh

@@ -887,6 +887,18 @@ test_expect_success 'log --pretty with magical wrapping directives' '
 	test_cmp expect actual
 '
 
+test_expect_success SIZE_T_IS_64BIT 'log --pretty with overflowing wrapping directive' '
+	cat >expect <<-EOF &&
+	fatal: number too large to represent as int on this platform: 2147483649
+	EOF
+	test_must_fail git log -1 --pretty="format:%w(2147483649,1,1)%d" 2>error &&
+	test_cmp expect error &&
+	test_must_fail git log -1 --pretty="format:%w(1,2147483649,1)%d" 2>error &&
+	test_cmp expect error &&
+	test_must_fail git log -1 --pretty="format:%w(1,1,2147483649)%d" 2>error &&
+	test_cmp expect error
+'
+
 test_expect_success EXPENSIVE,SIZE_T_IS_64BIT 'log --pretty with huge commit message' '
 	# We only assert that this command does not crash. This needs to be
 	# executed with the address sanitizer to demonstrate failure.