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unionfs: prevent upperrootvp from being recycled during mount

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If upperrootvp is doomed by a concurrent unmount, unionfs_nodeget()
may return without a reference or lock on it.  unionfs_domount() must
prevent the vnode from being recycled for use by a different file until
it is finished with the vnode, namely once vfs_register_upper_from_vp()
fails.  Accomplish this by holding the reference returned by namei()
a bit longer.

Reviewed by:	kib, markj
Tested by:	pho
Differential Revision:	https://reviews.freebsd.org/D39767
This commit is contained in:
Jason A. Harmening 2023-03-25 20:41:33 -05:00
parent 0809172985
commit 0745d837c2
1 changed files with 14 additions and 1 deletions
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15
sys/fs/unionfs/union_vfsops.c
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@ -285,8 +285,8 @@ unionfs_domount(struct mount *mp)
*/
error = unionfs_nodeget(mp, ump->um_uppervp, ump->um_lowervp,
NULLVP, &(ump->um_rootvp), NULL);
vrele(upperrootvp);
if (error != 0) {
vrele(upperrootvp);
free(ump, M_UNIONFSMNT);
mp->mnt_data = NULL;
return (error);
@ -295,11 +295,24 @@ unionfs_domount(struct mount *mp)
KASSERT((ump->um_rootvp->v_vflag & VV_ROOT) != 0,
("%s: rootvp without VV_ROOT", __func__));
/*
* Do not release the namei() reference on upperrootvp until after
* we attempt to register the upper mounts. A concurrent unmount
* of the upper or lower FS may have caused unionfs_nodeget() to
* create a unionfs node with a NULL upper or lower vp and with
* no reference held on upperrootvp or lowerrootvp.
* vfs_register_upper() should subsequently fail, which is what
* we want, but we must ensure neither underlying vnode can be
* reused until that happens. We assume the caller holds a reference
* to lowerrootvp as it is the mount's covered vnode.
*/
lowermp = vfs_register_upper_from_vp(ump->um_lowervp, mp,
&ump->um_lower_link);
uppermp = vfs_register_upper_from_vp(ump->um_uppervp, mp,
&ump->um_upper_link);
vrele(upperrootvp);
if (lowermp == NULL || uppermp == NULL) {
if (lowermp != NULL)
vfs_unregister_upper(lowermp, &ump->um_lower_link);