To reproduce:
$ dd if=/dev/null of=/tmp/dd.test bs=1m seek=$((1 << 24))
0+0 records in
0+0 records out
0 bytes transferred in 0.000 secs (0 bytes/sec)
$
Patch:
diff -rup /usr/src/bin/dd/dd.c dd/dd.c
--- /usr/src/bin/dd/dd.c Sun Oct 24 23:24:21 2021
+++ dd/dd.c Thu May 19 20:29:31 2022
@@ -161,7 +161,8 @@ setup(void)
* kinds of output files, tapes, for example.
*/
if ((ddflags & (C_OF | C_SEEK | C_NOTRUNC)) == (C_OF | C_SEEK))
- (void)ftruncate(out.fd, out.offset * out.dbsz);
+ if (ftruncate(out.fd, out.offset * out.dbsz) && (out.flags &
ISREG))
+ err(1, "%s", out.name);
/*
* If converting case at the same time as another conversion, build a
@@ -212,6 +213,8 @@ getfdtype(IO *io)
io->flags |= ioctl(io->fd, MTIOCGET, &mt) ? ISCHR : ISTAPE;
if (S_ISFIFO(sb.st_mode) || S_ISSOCK(sb.st_mode))
io->flags |= ISPIPE;
+ if (S_ISREG(sb.st_mode))
+ io->flags |= ISREG;
}
static void
diff -rup /usr/src/bin/dd/dd.h dd/dd.h
--- /usr/src/bin/dd/dd.h Sat Feb 16 11:54:00 2019
+++ dd/dd.h Sat May 7 02:49:15 2022
@@ -47,7 +47,8 @@ typedef struct {
#define ISCHR 0x01 /* character device (warn on
short) */
#define ISPIPE 0x02 /* pipe (not truncatable) */
#define ISTAPE 0x04 /* tape (not seekable) */
-#define NOREAD 0x08 /* not readable */
+#define ISREG 0x08 /* regular file (warn on
truncation errors) */
+#define NOREAD 0x10 /* not readable */
u_int flags;
char *name; /* name */
