Fix the race between dotdot lookup and forced unmount, by using
msdosfs-specific variant of vn_vget_ino(), msdosfs_deget_dotdot(). As was done for UFS, relookup the dotdot denode after the call to msdosfs_deget_dotdot(), because vnode lock is dropped and directory might be moved. Tested by: pho MFC after: 3 weeks
This commit is contained in:
parent
30e65ad1bb
commit
db811dd724
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=204474
@ -61,6 +61,18 @@
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#include <fs/msdosfs/fat.h>
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#include <fs/msdosfs/msdosfsmount.h>
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static int msdosfs_lookup_(struct vnode *vdp, struct vnode **vpp,
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struct componentname *cnp, u_int64_t *inum);
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static int msdosfs_deget_dotdot(struct vnode *vp, u_long cluster, int blkoff,
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struct vnode **rvp);
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int
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msdosfs_lookup(struct vop_cachedlookup_args *ap)
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{
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return (msdosfs_lookup_(ap->a_dvp, ap->a_vpp, ap->a_cnp, NULL));
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}
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/*
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* When we search a directory the blocks containing directory entries are
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* read and examined. The directory entries contain information that would
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@ -76,18 +88,11 @@
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* out to disk. This way disk blocks containing directory entries and in
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* memory denode's will be in synch.
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*/
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int
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msdosfs_lookup(ap)
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struct vop_cachedlookup_args /* {
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struct vnode *a_dvp;
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struct vnode **a_vpp;
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struct componentname *a_cnp;
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} */ *ap;
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static int
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msdosfs_lookup_(struct vnode *vdp, struct vnode **vpp,
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struct componentname *cnp, u_int64_t *dd_inum)
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{
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struct mbnambuf nb;
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struct vnode *vdp = ap->a_dvp;
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struct vnode **vpp = ap->a_vpp;
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struct componentname *cnp = ap->a_cnp;
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daddr_t bn;
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int error;
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int slotcount;
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@ -109,6 +114,7 @@ msdosfs_lookup(ap)
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int flags = cnp->cn_flags;
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int nameiop = cnp->cn_nameiop;
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int unlen;
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u_int64_t inode1;
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int wincnt = 1;
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int chksum = -1, chksum_ok;
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@ -119,12 +125,14 @@ msdosfs_lookup(ap)
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#endif
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dp = VTODE(vdp);
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pmp = dp->de_pmp;
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*vpp = NULL;
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if (vpp != NULL)
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*vpp = NULL;
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#ifdef MSDOSFS_DEBUG
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printf("msdosfs_lookup(): vdp %p, dp %p, Attr %02x\n",
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vdp, dp, dp->de_Attributes);
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#endif
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restart:
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/*
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* If they are going after the . or .. entry in the root directory,
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* they won't find it. DOS filesystems don't have them in the root
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@ -436,6 +444,11 @@ msdosfs_lookup(ap)
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if (FAT32(pmp) && scn == MSDOSFSROOT)
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scn = pmp->pm_rootdirblk;
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if (dd_inum != NULL) {
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*dd_inum = (uint64_t)pmp->pm_bpcluster * scn + blkoff;
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return (0);
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}
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/*
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* If deleting, and at end of pathname, return
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* parameters which can be used to remove file.
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@ -508,23 +521,25 @@ msdosfs_lookup(ap)
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* inodes from the root, moving down the directory tree. Thus
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* when following backward pointers ".." we must unlock the
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* parent directory before getting the requested directory.
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* There is a potential race condition here if both the current
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* and parent directories are removed before the VFS_VGET for the
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* inode associated with ".." returns. We hope that this occurs
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* infrequently since we cannot avoid this race condition without
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* implementing a sophisticated deadlock detection algorithm.
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* Note also that this simple deadlock detection scheme will not
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* work if the filesystem has any hard links other than ".."
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* that point backwards in the directory structure.
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*/
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pdp = vdp;
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if (flags & ISDOTDOT) {
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VOP_UNLOCK(pdp, 0);
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error = deget(pmp, cluster, blkoff, &tdp);
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vn_lock(pdp, LK_EXCLUSIVE | LK_RETRY);
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error = msdosfs_deget_dotdot(pdp, cluster, blkoff, vpp);
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if (error)
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return (error);
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*vpp = DETOV(tdp);
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/*
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* Recheck that ".." still points to the inode we
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* looked up before pdp lock was dropped.
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*/
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error = msdosfs_lookup_(pdp, NULL, cnp, &inode1);
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if (error) {
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vput(*vpp);
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return (error);
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}
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if (VTODE(*vpp)->de_inode != inode1) {
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vput(*vpp);
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goto restart;
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}
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} else if (dp->de_StartCluster == scn && isadir) {
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VREF(vdp); /* we want ourself, ie "." */
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*vpp = vdp;
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@ -542,6 +557,49 @@ msdosfs_lookup(ap)
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return (0);
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}
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static int
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msdosfs_deget_dotdot(struct vnode *vp, u_long cluster, int blkoff,
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struct vnode **rvp)
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{
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struct mount *mp;
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struct msdosfsmount *pmp;
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struct denode *rdp;
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int ltype, error;
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mp = vp->v_mount;
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pmp = VFSTOMSDOSFS(mp);
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ltype = VOP_ISLOCKED(vp);
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KASSERT(ltype == LK_EXCLUSIVE || ltype == LK_SHARED,
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("msdosfs_deget_dotdot: vp not locked"));
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error = vfs_busy(mp, MBF_NOWAIT);
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if (error != 0) {
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vfs_ref(mp);
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VOP_UNLOCK(vp, 0);
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error = vfs_busy(mp, 0);
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vn_lock(vp, ltype | LK_RETRY);
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vfs_rel(mp);
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if (error != 0)
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return (ENOENT);
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if (vp->v_iflag & VI_DOOMED) {
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vfs_unbusy(mp);
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return (ENOENT);
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}
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}
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VOP_UNLOCK(vp, 0);
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error = deget(pmp, cluster, blkoff, &rdp);
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vfs_unbusy(mp);
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if (error == 0)
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*rvp = DETOV(rdp);
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vn_lock(vp, ltype | LK_RETRY);
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if (vp->v_iflag & VI_DOOMED) {
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if (error == 0)
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vput(*rvp);
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error = ENOENT;
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}
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return (error);
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}
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/*
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* dep - directory entry to copy into the directory
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* ddep - directory to add to
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