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From: =?utf-8?b?0L3QsNCx?= <nabijaczleweli@nabijaczleweli.xyz>
Date: Fri, 29 Nov 2024 22:55:19 +0100
Subject: Fix printf() parser treating field width as array length for strings
(Closes: #804494)
Given:
#include <stdio.h>
int main() {
printf("'%8.4s' '%8s' '%.4s'\n", "1234567890", "1234567890", "1234567890");
printf("'%*.*s' '%*s' '%.*s'\n", 8, 4, "1234567890", 8, "1234567890", 4, "1234567890");
}
Compare:
$ ./ltrace.before -F etc ./q | cat
printf("'%8.4s' '%8s' '%.4s'\n", "1234567890", "12345678", "1234") = 31
printf("'%*.*s' '%*s' '%.*s'\n", 8, 4, "1234", 8, "12345678", 4, "1234") = 31
' 1234' '1234567890' '1234'
' 1234' '1234567890' '1234'
+++ exited (status 0) +++
$ ./ltrace.after -F etc ./q | cat
printf("'%8.4s' '%8s' '%.4s'\n", "1234", "1234567890", "1234") = 31
printf("'%*.*s' '%*s' '%.*s'\n", 8, 4, "1234", 8, "1234567890", 4, "1234") = 31
' 1234' '1234567890' '1234'
' 1234' '1234567890' '1234'
+++ exited (status 0) +++
Of course, printf("%2$s") is still hopeless. But!
---
printf.c | 72 +++++++++++++++++++++++++++++-----------------------------------
1 file changed, 32 insertions(+), 40 deletions(-)
diff --git a/printf.c b/printf.c
index ea18982..f54e59f 100644
--- a/printf.c
+++ b/printf.c
@@ -38,7 +38,8 @@
struct param_enum {
struct value array;
int percent;
- unsigned long long *future_length;
+ bool have_future_precision;
+ unsigned long long future_precision;
char *format;
char const *ptr;
char const *end;
@@ -107,23 +108,14 @@ param_printf_init(struct value *cb_args, size_t nargs,
self->percent = 0;
self->ptr = self->format;
self->end = self->format + size;
- self->future_length = NULL;
+ self->have_future_precision = false;
return self;
}
-static void
-drop_future_length(struct param_enum *self)
-{
- if (self->future_length != NULL) {
- free(self->future_length);
- self->future_length = NULL;
- }
-}
-
static int
form_next_param(struct param_enum *self,
enum arg_type format_type, enum arg_type elt_type,
- unsigned hlf, unsigned lng, char *len_buf, size_t len_buf_len,
+ unsigned hlf, unsigned lng, char *prec_buf, size_t prec_buf_len,
struct arg_type_info *infop)
{
/* XXX note: Some types are wrong because we lack
@@ -153,8 +145,8 @@ form_next_param(struct param_enum *self,
struct expr_node *node = NULL;
int own_node;
- if (len_buf_len != 0
- || self->future_length != NULL) {
+ if (prec_buf_len != 0
+ || self->have_future_precision) {
struct tmp {
struct expr_node node;
struct arg_type_info type;
@@ -170,11 +162,11 @@ form_next_param(struct param_enum *self,
len->type = *type_get_simple(ARGTYPE_LONG);
long l;
- if (self->future_length != NULL) {
- l = *self->future_length;
- drop_future_length(self);
+ if (self->have_future_precision) {
+ l = self->future_precision;
+ self->have_future_precision = false;
} else {
- l = atol(len_buf);
+ l = atol(prec_buf);
}
expr_init_const_word(&len->node, l, &len->type, 0);
@@ -211,10 +203,10 @@ param_printf_next(struct param_enum *self, struct arg_type_info *infop,
unsigned lng = 0;
enum arg_type format_type = ARGTYPE_VOID;
enum arg_type elt_type = ARGTYPE_VOID;
- char len_buf[25] = {};
- size_t len_buf_len = 0;
+ char prec_buf[25] = {};
+ size_t prec_buf_len = 0;
struct lens *lens = NULL;
- bool digital_width = false, digital_width_fast = false;
+ bool digital_width = false, digital_width_fast = false, in_precision = false;
for (; self->ptr < self->end; self->ptr += self->width) {
union {
@@ -245,21 +237,20 @@ param_printf_next(struct param_enum *self, struct arg_type_info *infop,
* not for interpreting the type. */
continue;
+ case '.':
+ /* Digits and * we see now apply to precision, not width.
+ * This mostly matters for %s. */
+ in_precision = true;
+ continue;
+
case '*':
/* Length parameter given in the next
* argument. */
- if (self->future_length == NULL)
- /* This should really be an assert,
- * but we can't just fail on invalid
- * format string. */
- self->future_length
- = malloc(sizeof(*self->future_length));
-
- if (self->future_length != NULL) {
- self->ptr += self->width;
- format_type = ARGTYPE_INT;
- break;
- }
+ if (in_precision)
+ self->have_future_precision = true;
+ self->ptr += self->width;
+ format_type = ARGTYPE_INT;
+ break;
case '0':
case '1': case '2': case '3':
@@ -268,9 +259,10 @@ param_printf_next(struct param_enum *self, struct arg_type_info *infop,
if(!digital_width) {
/* Field length likewise, but we need to parse
* this to attach the appropriate string
- * length expression. */
- if (len_buf_len < sizeof(len_buf) - 1)
- len_buf[len_buf_len++] = c;
+ * length expression.
+ * We don't care about width. */
+ if (in_precision && prec_buf_len < sizeof(prec_buf) - 1)
+ prec_buf[prec_buf_len++] = c;
} else {
/* %w32d */
digital_width = false;
@@ -420,7 +412,7 @@ param_printf_next(struct param_enum *self, struct arg_type_info *infop,
assert(format_type != ARGTYPE_VOID);
if (form_next_param(self, format_type, elt_type, hlf, lng,
- len_buf, len_buf_len, infop) < 0)
+ prec_buf, prec_buf_len, infop) < 0)
return -1;
infop->lens = lens;
@@ -437,9 +429,9 @@ err:
static enum param_status
param_printf_stop(struct param_enum *self, struct value *value)
{
- if (self->future_length != NULL
- && value_extract_word(value, (long long *)self->future_length, NULL) < 0)
- drop_future_length(self);
+ if (self->have_future_precision
+ && value_extract_word(value, (long long *)&self->future_precision, NULL) < 0)
+ self->have_future_precision = false;
return PPCB_CONT;
}
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