mkswap: clear 1st kilobyte. Closes bug 1831

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/util-linux/mkswap.c b/util-linux/mkswap.c
index 3f736faba..61a786e92 100644
--- a/util-linux/mkswap.c
+++ b/util-linux/mkswap.c
@@ -102,7 +102,15 @@ int mkswap_main(int argc UNUSED_PARAM, char **argv)
         printf("Setting up swapspace version 1, size = %"OFF_FMT"u bytes\n", len);
         mkswap_selinux_setcontext(fd, argv[0]);
 
-        /* Make a header. hdr is zero-filled so far... */
+        /* hdr is zero-filled so far. Clear the first kbyte, or else
+         * mkswap-ing former FAT partition does NOT erase its signature.
+         *
+         * util-linux-ng 2.17.2 claims to erase it only if it does not see
+         * a partition table and is not run on whole disk. -f forces it.
+         */
+        xwrite(fd, hdr, 1024);
+
+        /* Fill the header. */
         hdr->version = 1;
         hdr->last_page = (uoff_t)len / pagesize;
 
@@ -123,7 +131,6 @@ int mkswap_main(int argc UNUSED_PARAM, char **argv)
 
         /* Write the header.  Sync to disk because some kernel versions check
          * signature on disk (not in cache) during swapon. */
-        xlseek(fd, 1024, SEEK_SET);
         xwrite(fd, hdr, NWORDS * 4);
         xlseek(fd, pagesize - 10, SEEK_SET);
         xwrite(fd, SWAPSPACE2, 10);