git: 764ccf410c3c - main - makefs: Ensure that FFS superblocks are reproducible

The branch main has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=764ccf410c3c5453c4656113d75cd81fcf01828d

commit 764ccf410c3c5453c4656113d75cd81fcf01828d
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2025-05-08 15:49:53 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2025-05-08 15:49:53 +0000

    makefs: Ensure that FFS superblocks are reproducible
    
    The superblock structure has space reserved for a pointer to an
    in-memory structure that gets created at mount time.  makefs populates
    it since that simplifies code elsewhere.  However, the pointer value
    ends up in the output file, which breaks reproducibility.
    
    Zero the field when writing the superblock instead, as its on-disk value
    is ignored.
    
    Reviewed by:    emaste
    MFC after:      2 weeks
    Sponsored by:   Klara, Inc.
    Sponsored by:   The FreeBSD Foundation
    Differential Revision:  https://reviews.freebsd.org/D50196
---
 usr.sbin/makefs/ffs/mkfs.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/usr.sbin/makefs/ffs/mkfs.c b/usr.sbin/makefs/ffs/mkfs.c
index b2f752102a69..81e3da5725c8 100644
--- a/usr.sbin/makefs/ffs/mkfs.c
+++ b/usr.sbin/makefs/ffs/mkfs.c
@@ -579,13 +579,21 @@ ffs_write_superblock(struct fs *fs, const fsinfo_t *fsopts)
 {
 	int size, blks, i, saveflag;
 	uint32_t cylno;
-	void *space;
+	void *info, *space;
 	char *wrbuf;
 
 	saveflag = fs->fs_flags & FS_INTERNAL;
 	fs->fs_flags &= ~FS_INTERNAL;
 
-        memcpy(writebuf, &sblock, sbsize);
+	/*
+	 * Write out the superblock.  Blank out the summary info field, as it's
+	 * a random pointer that would make the resulting image unreproducible.
+	 */
+	info = fs->fs_si;
+	fs->fs_si = NULL;
+	memcpy(writebuf, fs, sbsize);
+	fs->fs_si = info;
+
 	if (fsopts->needswap)
 		ffs_sb_swap(fs, (struct fs*)writebuf);
 	ffs_wtfs(fs->fs_sblockloc / sectorsize, sbsize, writebuf, fsopts);