Make TIFF parsing a bit safer

At least on 64-bit systems, 32-bit may still have holes.

fiv-io.c

@@ -1844,11 +1844,10 @@ tiff_ep_find_jpeg_evaluate(const struct tiffer *T, struct tiff_ep_jpeg *out)
 	}
 
 	int64_t ipointer = 0, ilength = 0;
-	if (!tiffer_find_integer(T, tag_pointer, &ipointer) ||
-		!tiffer_find_integer(T, tag_length, &ilength) ||
-		ipointer <= 0 || ilength <= 0 ||
-		(uint64_t) ilength > SIZE_MAX ||
-		ipointer + ilength > (T->end - T->begin))
+	if (!tiffer_find_integer(T, tag_pointer, &ipointer) || ipointer <= 0 ||
+		!tiffer_find_integer(T, tag_length, &ilength) || ilength <= 0 ||
+		ipointer > T->end - T->begin ||
+		T->end - T->begin - ipointer < ilength)
 		return;
 
 	// Note that to get the largest JPEG,

tiffer.h

@@ -15,9 +15,10 @@
 // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 //
 
+#include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <string.h>
-#include <stdbool.h>
 
 // --- Utilities ---------------------------------------------------------------
 
@@ -85,7 +86,7 @@ struct tiffer {
 static bool
 tiffer_u32(struct tiffer *self, uint32_t *u)
 {
-	if (self->p < self->begin || self->p + 4 > self->end)
+	if (self->end - self->p < 4)
 		return false;
 
 	*u = self->un->u32(self->p);
@@ -96,7 +97,7 @@ tiffer_u32(struct tiffer *self, uint32_t *u)
 static bool
 tiffer_u16(struct tiffer *self, uint16_t *u)
 {
-	if (self->p < self->begin || self->p + 2 > self->end)
+	if (self->end - self->p < 2)
 		return false;
 
 	*u = self->un->u16(self->p);
@@ -160,6 +161,9 @@ static bool
 tiffer_subifd(
 	const struct tiffer *self, uint32_t offset, struct tiffer *subreader)
 {
+	if (self->end - self->begin < offset)
+		return false;
+
 	*subreader = *self;
 	subreader->p = subreader->begin + offset;
 	return tiffer_u16(subreader, &subreader->remaining_fields);
@@ -323,14 +327,15 @@ tiffer_next_entry(struct tiffer *self, struct tiffer_entry *entry)
 	if (values_size <= sizeof offset) {
 		entry->p = self->p;
 		self->p += sizeof offset;
-	} else if (tiffer_u32(self, &offset)) {
+	} else if (tiffer_u32(self, &offset) && self->end - self->begin >= offset) {
 		entry->p = self->begin + offset;
 	} else {
 		return false;
 	}
 
 	// All entries are pre-checked not to overflow.
-	if (entry->p + values_size > self->end)
+	if (values_size > PTRDIFF_MAX ||
+		self->end - entry->p < (ptrdiff_t) values_size)
 		return false;
 
 	// Setting it at the end may provide an indication while debugging.

tools/info.h

@@ -92,8 +92,8 @@ static jv parse_jpeg(jv o, const uint8_t *p, size_t len);
 static jv parse_exif_ifd(struct tiffer *T, const struct tiff_entry *info);
 
 static bool
-parse_exif_subifds_entry(struct tiffer *T, const struct tiffer_entry *entry,
-	struct tiffer *subT)
+parse_exif_subifds_entry(const struct tiffer *T,
+	const struct tiffer_entry *entry, struct tiffer *subT)
 {
 	int64_t offset = 0;
 	return tiffer_integer(T, entry, &offset) &&
@@ -101,7 +101,7 @@ parse_exif_subifds_entry(struct tiffer *T, const struct tiffer_entry *entry,
 }
 
 static jv
-parse_exif_subifds(struct tiffer *T, struct tiffer_entry *entry,
+parse_exif_subifds(const struct tiffer *T, struct tiffer_entry *entry,
 	struct tiff_entry *info)
 {
 	struct tiffer subT = {};
@@ -173,7 +173,7 @@ parse_exif_extract_sole_array_element(jv a)
 }
 
 static jv
-parse_exif_entry(jv o, struct tiffer *T, struct tiffer_entry *entry,
+parse_exif_entry(jv o, const struct tiffer *T, struct tiffer_entry *entry,
 	const struct tiff_entry *info)
 {
 	static struct tiff_entry empty[] = {{}};
@@ -679,7 +679,7 @@ static struct tiff_entry mpf_entries[] = {
 };
 
 static uint32_t
-parse_mpf_mpentry(jv *a, const uint8_t *p, struct tiffer *T)
+parse_mpf_mpentry(jv *a, const uint8_t *p, const struct tiffer *T)
 {
 	uint32_t attrs = T->un->u32(p);
 	uint32_t offset = T->un->u32(p + 8);
@@ -725,7 +725,7 @@ parse_mpf_mpentry(jv *a, const uint8_t *p, struct tiffer *T)
 }
 
 static jv
-parse_mpf_index_entry(jv o, const uint8_t ***offsets, struct tiffer *T,
+parse_mpf_index_entry(jv o, const uint8_t ***offsets, const struct tiffer *T,
 	struct tiffer_entry *entry)
 {
 	// 5.2.3.3. MP Entry
@@ -738,6 +738,9 @@ parse_mpf_index_entry(jv o, const uint8_t ***offsets, struct tiffer *T,
 	jv a = jv_array_sized(count);
 	const uint8_t **out = *offsets = calloc(sizeof *out, count + 1);
 	for (uint32_t i = 0; i < count; i++) {
+		// 5.2.3.3.3. Individual Image Data Offset
+		// XXX: We might want to warn about out-of-bounds pointers,
+		// however T->end is for the MPF segment and ends too early.
 		uint32_t offset = parse_mpf_mpentry(&a, entry->p + i * 16, T);
 		if (offset)
 			*out++ = T->begin + offset;