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msdosfs: zero partially valid extended cluster

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It contains arbitrary garbage, which is not cleared by vfs_bio_clrbuf()
which only zeroes invalid portions of the pages.

Reported by:	Maxim Suhanov <dfirblog@gmail.com>
Discussed with:	so
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
This commit is contained in:
Konstantin Belousov 2023-07-06 04:51:07 +03:00
parent f3674213e3
commit 7e4c6b2163
1 changed files with 8 additions and 1 deletions
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9
sys/fs/msdosfs/msdosfs_denode.c
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@ -498,6 +498,7 @@ deextend(struct denode *dep, u_long length, struct ucred *cred)
struct msdosfsmount *pmp = dep->de_pmp;
struct vnode *vp = DETOV(dep);
struct buf *bp;
off_t eof_clusteroff;
u_long count;
int error;
@ -536,13 +537,19 @@ deextend(struct denode *dep, u_long length, struct ucred *cred)
* B_CACHE | B_DELWRI but with invalid pages, and cannot be
* neither written out nor validated.
*
* Fix it by proactively clearing extended pages.
* Fix it by proactively clearing extended pages. Need to do
* both vfs_bio_clrbuf() to mark pages valid, and to zero
* actual buffer content which might exist in the tail of the
* already valid cluster.
*/
error = bread(vp, de_cluster(pmp, dep->de_FileSize), pmp->pm_bpcluster,
NOCRED, &bp);
if (error != 0)
goto rewind;
vfs_bio_clrbuf(bp);
eof_clusteroff = de_cn2off(pmp, de_cluster(pmp, dep->de_FileSize));
vfs_bio_bzero_buf(bp, dep->de_FileSize - eof_clusteroff,
pmp->pm_bpcluster - dep->de_FileSize + eof_clusteroff);
if (!DOINGASYNC(vp))
(void)bwrite(bp);
else if (vm_page_count_severe() || buf_dirty_count_severe())