git: 0152d453a08f - main - msdosfs deextend: validate pages of the partial buffer

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=0152d453a08fa2bad694dc04a8184fce2b7faa10

commit 0152d453a08fa2bad694dc04a8184fce2b7faa10
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2023-02-11 18:09:30 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2023-02-13 22:29:42 +0000

    msdosfs deextend: validate pages of the partial buffer
    
    Suppose that the cluster size is larger than page size. If the buffer
    at the old EOF (before extending) was partial and dirty, it cannot be
    automatically neither written out nor validated by the buffer cache,
    since extending buffer adds invalid pages at the end.
    
    Correct the buffer state by calling vfs_bio_clrbuf() on it, to mark
    newly added and zeroed pages as valid.
    
    Note that UFS is immune to the problem because ffs_truncate() always
    allocate the block and buffer for the last byte of the file.
    
    PR:     269341
    Reported by:    asomers
    In collaboration with:  pho
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Differential revision:  https://reviews.freebsd.org/D38549
---
 sys/fs/msdosfs/msdosfs_denode.c | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/sys/fs/msdosfs/msdosfs_denode.c b/sys/fs/msdosfs/msdosfs_denode.c
index 0b4135d60784..a82517acbdfe 100644
--- a/sys/fs/msdosfs/msdosfs_denode.c
+++ b/sys/fs/msdosfs/msdosfs_denode.c
@@ -497,6 +497,7 @@ deextend(struct denode *dep, u_long length, struct ucred *cred)
 {
 	struct msdosfsmount *pmp = dep->de_pmp;
 	struct vnode *vp = DETOV(dep);
+	struct buf *bp;
 	u_long count;
 	int error;
 
@@ -523,16 +524,41 @@ deextend(struct denode *dep, u_long length, struct ucred *cred)
 		if (count > pmp->pm_freeclustercount)
 			return (ENOSPC);
 		error = extendfile(dep, count, NULL, NULL, DE_CLEAR);
-		if (error) {
-			/* truncate the added clusters away again */
-			(void) detrunc(dep, dep->de_FileSize, 0, cred);
-			return (error);
-		}
+		if (error != 0)
+			goto rewind;
 	}
+
+	/*
+	 * For the case of cluster size larger than the page size, we
+	 * need to ensure that the possibly dirty partial buffer at
+	 * the old end of file is not filled with invalid pages by
+	 * extension.  Otherwise it has a contradictory state of
+	 * B_CACHE | B_DELWRI but with invalid pages, and cannot be
+	 * neither written out nor validated.
+	 *
+	 * Fix it by proactively clearing extended pages.
+	 */
+	error = bread(vp, de_cluster(pmp, dep->de_FileSize), pmp->pm_bpcluster,
+	    NOCRED, &bp);
+	if (error != 0)
+		goto rewind;
+	vfs_bio_clrbuf(bp);
+	if (!DOINGASYNC(vp))
+		(void)bwrite(bp);
+	else if (vm_page_count_severe() || buf_dirty_count_severe())
+		bawrite(bp);
+	else
+		bdwrite(bp);
+
 	vnode_pager_setsize(vp, length);
 	dep->de_FileSize = length;
 	dep->de_flag |= DE_UPDATE | DE_MODIFIED;
 	return (deupdat(dep, !DOINGASYNC(vp)));
+
+rewind:
+	/* truncate the added clusters away again */
+	(void)detrunc(dep, dep->de_FileSize, 0, cred);
+	return (error);
 }
 
 /*