Fix unsigned < 0 check

Two places in malware.c were using `fsize`, defined as `unsigned int`,
to receive the result of `lseek()` and then checking if the value was
less than 0.  As clang says:

```
malware.c:1228:46: warning: comparison of unsigned expression < 0 is always false [-Wtautological-compare]
          if ((fsize = lseek(clam_fd, 0, SEEK_END)) < 0) {
              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~
```

Fix.  Use `off_t`, which we're already using elsewhere, then use
`fsize_uint` to handle off_t being potentially 64-bit, and a
sanity-check on conversion which hopefully won't be optimised away by
compilers.

1 files changed, 28 insertions, 10 deletions

diff --git a/src/src/malware.c b/src/src/malware.c
index 7685554ae..04b5887e7 100644
--- a/src/src/malware.c
+++ b/src/src/malware.c
@@ -456,7 +456,8 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
     /* v0.0 - initial release -- support for unix sockets      */
       {
 	int result;
-	unsigned int fsize;
+	off_t fsize;
+	unsigned int fsize_uint;
 	uschar * tmpbuf, *drweb_fbuf;
 	int drweb_rc, drweb_cmd, drweb_flags = 0x0000, drweb_fd,
 	    drweb_vnum, drweb_slen, drweb_fin = 0x0000;
@@ -484,6 +485,14 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 		eml_filename, strerror(err)),
 	      sock);
 	  }
+	  fsize_uint = (unsigned int) fsize;
+	  if ((off_t)fsize_uint != fsize) {
+	    (void)close(drweb_fd);
+	    return m_errlog_defer_3(scanent,
+	      string_sprintf("seeking spool file %s, size overflow",
+		eml_filename),
+	      sock);
+	  }
 	  drweb_slen = htonl(fsize);
 	  lseek(drweb_fd, 0, SEEK_SET);
 
@@ -501,11 +510,11 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 	      sock);
 	  }
 
-	  if (!(drweb_fbuf = (uschar *) malloc (fsize))) {
+	  if (!(drweb_fbuf = (uschar *) malloc (fsize_uint))) {
 	    (void)close(drweb_fd);
 	    return m_errlog_defer_3(scanent,
 	      string_sprintf("unable to allocate memory %u for file (%s)",
-		fsize, eml_filename),
+		fsize_uint, eml_filename),
 	      sock);
 	  }
 
@@ -1035,7 +1044,8 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 	host_item connhost;
 	uschar *clamav_fbuf;
 	int clam_fd, result;
-	unsigned int fsize;
+	off_t fsize;
+	unsigned int fsize_uint;
 	BOOL use_scan_command = FALSE;
 	clamd_address_container * clamd_address_vector[MAX_CLAMD_SERVERS];
 	int current_server;
@@ -1231,17 +1241,25 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 		eml_filename, strerror(err)),
 	      sock);
 	  }
+	  fsize_uint = (unsigned int) fsize;
+	  if ((off_t)fsize_uint != fsize) {
+	    CLOSE_SOCKDATA; (void)close(clam_fd);
+	    return m_errlog_defer_3(scanent,
+	      string_sprintf("seeking spool file %s, size overflow",
+		eml_filename),
+	      sock);
+	  }
 	  lseek(clam_fd, 0, SEEK_SET);
 
-	  if (!(clamav_fbuf = (uschar *) malloc (fsize))) {
+	  if (!(clamav_fbuf = (uschar *) malloc (fsize_uint))) {
 	    CLOSE_SOCKDATA; (void)close(clam_fd);
 	    return m_errlog_defer_3(scanent,
 	      string_sprintf("unable to allocate memory %u for file (%s)",
-		fsize, eml_filename),
+		fsize_uint, eml_filename),
 	      sock);
 	  }
 
-	  if ((result = read(clam_fd, clamav_fbuf, fsize)) < 0) {
+	  if ((result = read(clam_fd, clamav_fbuf, fsize_uint)) < 0) {
 	    int err = errno;
 	    free(clamav_fbuf); CLOSE_SOCKDATA; (void)close(clam_fd);
 	    return m_errlog_defer_3(scanent,
@@ -1253,7 +1271,7 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 
 	  /* send file body to socket */
   #ifdef WITH_OLD_CLAMAV_STREAM
-	  if (send(sockData, clamav_fbuf, fsize, 0) < 0) {
+	  if (send(sockData, clamav_fbuf, fsize_uint, 0) < 0) {
 	    free(clamav_fbuf); CLOSE_SOCKDATA;
 	    return m_errlog_defer_3(scanent,
 	      string_sprintf("unable to send file body to socket (%s:%u)",
@@ -1261,10 +1279,10 @@ malware_internal(uschar **listptr, uschar *eml_filename, BOOL faking)
 	      sock);
 	  }
   #else
-	  send_size = htonl(fsize);
+	  send_size = htonl(fsize_uint);
 	  send_final_zeroblock = 0;
 	  if ((send(sock, &send_size, sizeof(send_size), 0) < 0) ||
-	      (send(sock, clamav_fbuf, fsize, 0) < 0) ||
+	      (send(sock, clamav_fbuf, fsize_uint, 0) < 0) ||
 	      (send(sock, &send_final_zeroblock, sizeof(send_final_zeroblock), 0) < 0))
 	    {
 	    free(clamav_fbuf);