fgetpos32 does not signal overflow when [63:32] bits of position offset are
non-zero, and returns truncated value. fgetpos32 signals overflow only when
[31] bit is set. Implement simple overflow check by comparing the returned
position value with raw offset from _lseeki64().
---
mingw-w64-crt/stdio/fgetpos.c | 48 ++++++++++++++++++++++++++++++++++-
1 file changed, 47 insertions(+), 1 deletion(-)
diff --git a/mingw-w64-crt/stdio/fgetpos.c b/mingw-w64-crt/stdio/fgetpos.c
index 924c603c0295..aa3feda108e1 100644
--- a/mingw-w64-crt/stdio/fgetpos.c
+++ b/mingw-w64-crt/stdio/fgetpos.c
@@ -5,17 +5,63 @@
*/
#include <stdio.h>
+#include <errno.h>
+#include <limits.h>
+#include <io.h>
/* Define 64-bit fgetpos() function via 32-bit fgetpos32() function */
_CRTIMP int __cdecl fgetpos32(FILE *__restrict__ _File, long *__restrict__
_Pos);
int __cdecl fgetpos(FILE *__restrict__ _File, fpos_t *__restrict__ _Pos)
{
+ __int64 raw_off64;
long pos32;
int ret;
+ int fd;
+ int old_errno;
+ old_errno = errno;
+
+ /* Function fgetpos32() on success returns 0 and sets pos32 to [30:0] bits of
+ * 64-bit position offset. If the [31] bit of 64-bit position offset is set
+ * then fgetpos32() returns -1, sets pos32 to -1 and do not change errno.
+ * Non-zero value in [63:32] bits of 64-bit position offset does not trigger
+ * any error condition. In other error cases fgetpos32() returns -1,
+ * sets pos32 to -1 and errno to error value. */
+
+ errno = 0;
ret = fgetpos32(_File, &pos32);
+ if (ret != 0 || pos32 < 0)
+ {
+ if (errno == 0) /* This detects overflow when [31] bit is set. */
+ errno = EOVERFLOW;
+ *_Pos = pos32;
+ return ret;
+ }
+
+ /* Now try to detect overflow when [63:32] bits of offset are set.
+ * Do it by comparing the raw fd-based 64-bit offset returned by
+ * _lseeki64() that is not further than the half of the maximal
+ * possible 31-bit position offset returned by fgetpos32().
+ * Because FILE* stream use read/write buffers and translation modes,
+ * the FILE* stream position and raw fd position can be different
+ * and raw fd position be used directly for FILE* stream position.
+ */
+ fd = fileno(_File);
+ if (fd >= 0)
+ {
+ raw_off64 = _lseeki64(fd, 0, SEEK_CUR);
+ if (raw_off64 > LONG_MAX && raw_off64 - pos32 > LONG_MAX/2)
+ {
+ errno = EOVERFLOW;
+ *_Pos = -1;
+ return -1;
+ }
+ }
+
+ errno = old_errno;
+
*_Pos = pos32;
- return ret;
+ return 0;
}
int (__cdecl *__MINGW_IMP_SYMBOL(fgetpos))(FILE *__restrict__ _File, fpos_t
*__restrict__ _Pos) = fgetpos;
--
2.20.1
_______________________________________________
Mingw-w64-public mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
