Make fseek(... SEEK_CUR) fails if current file-position is unspecified.

2 files changed, 8 insertions, 8 deletions

diff --git a/lib/libc/stdio/fseek.3 b/lib/libc/stdio/fseek.3
index b08bbc8..fe7f313 100644
--- a/lib/libc/stdio/fseek.3
+++ b/lib/libc/stdio/fseek.3
@@ -206,12 +206,8 @@ for
 and
 .Fn ftell .
 .It Bq Er ESPIPE
-The file descriptor underlying stream is associated with a pipe or FIFO.
-For
-.Fn ftell
-and
-.Fn ftello ,
-file-position indicator value is unspecified
+The file descriptor underlying stream is associated with a pipe or FIFO
+or file-position indicator value is unspecified
 (see
 .Xr ungetc 3 ) .
 .El
diff --git a/lib/libc/stdio/fseek.c b/lib/libc/stdio/fseek.c
index d06e408..b2d98a9 100644
--- a/lib/libc/stdio/fseek.c
+++ b/lib/libc/stdio/fseek.c
@@ -131,8 +131,12 @@ _fseeko(fp, offset, whence, ltest)
 		 */
 		if (_ftello(fp, &curoff))
 			return (-1);
-		if ((offset > 0 && curoff > OFF_MAX - offset) ||
-		    (offset < 0 && curoff < OFF_MIN - offset)) {
+		if (curoff < 0) {
+			/* Unspecified position because of ungetc() at 0 */
+			errno = ESPIPE;
+			return (-1);
+		}
+		if (offset > 0 && curoff > OFF_MAX - offset) {
 			errno = EOVERFLOW;
 			return (-1);
 		}