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ceph: avoid dereferencing invalid pointer during cached readdir

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Readdir cache keeps array of dentry pointers in page cache. If any
dentry in readdir cache gets pruned, ceph_d_prune() disables readdir
cache for later readdir syscall. The problem is that ceph_d_prune()
ignores unhashed dentry. Ideally MDS should have already revoked
CEPH_CAP_FILE_SHARED (which also disables readdir cache) when dentry
gets unhashed. But if it is somehow MDS does not properly revoke
CEPH_CAP_FILE_SHARED and the unhashed dentry gets pruned later,
ceph_d_prune() will not disable readdir cache, later readdir may
reference invalid dentry pointer.

The fix is make ceph_d_prune() do extra check for unhashed dentry.
Disable readdir cache if the unhashed dentry is still referenced
by readdir cache.

Another fix in this patch is handle d_splice_alias(). If a dentry
gets spliced into new parent dentry, treat it as if it was pruned
(call ceph_d_prune() for it).

Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
This commit is contained in:
Yan, Zheng 2017-11-27 11:23:48 +08:00 committed by Ilya Dryomov
parent 97aeb6bf98
commit 5495c2d04f
2 changed files with 66 additions and 19 deletions
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45
fs/ceph/dir.c
View file

@ -231,11 +231,17 @@ static int __dcache_readdir(struct file *file, struct dir_context *ctx,
goto out;
}
di = ceph_dentry(dentry);
spin_lock(&dentry->d_lock);
if (di->lease_shared_gen == shared_gen &&
d_really_is_positive(dentry) &&
fpos_cmp(ctx->pos, di->offset) <= 0) {
di = ceph_dentry(dentry);
if (d_unhashed(dentry) ||
d_really_is_negative(dentry) ||
di->lease_shared_gen != shared_gen) {
spin_unlock(&dentry->d_lock);
dput(dentry);
err = -EAGAIN;
goto out;
}
if (fpos_cmp(ctx->pos, di->offset) <= 0) {
emit_dentry = true;
}
spin_unlock(&dentry->d_lock);
@ -1324,24 +1330,37 @@ static void ceph_d_release(struct dentry *dentry)
*/
static void ceph_d_prune(struct dentry *dentry)
{
dout("ceph_d_prune %p\n", dentry);
struct ceph_inode_info *dir_ci;
struct ceph_dentry_info *di;
dout("ceph_d_prune %pd %p\n", dentry, dentry);
/* do we have a valid parent? */
if (IS_ROOT(dentry))
return;
/* if we are not hashed, we don't affect dir's completeness */
if (d_unhashed(dentry))
/* we hold d_lock, so d_parent is stable */
dir_ci = ceph_inode(d_inode(dentry->d_parent));
if (dir_ci->i_vino.snap == CEPH_SNAPDIR)
return;
if (ceph_snap(d_inode(dentry->d_parent)) == CEPH_SNAPDIR)
/* who calls d_delete() should also disable dcache readdir */
if (d_really_is_negative(dentry))
return;
/*
* we hold d_lock, so d_parent is stable, and d_fsdata is never
* cleared until d_release
*/
ceph_dir_clear_complete(d_inode(dentry->d_parent));
/* d_fsdata does not get cleared until d_release */
if (!d_unhashed(dentry)) {
__ceph_dir_clear_complete(dir_ci);
return;
}
/* Disable dcache readdir just in case that someone called d_drop()
* or d_invalidate(), but MDS didn't revoke CEPH_CAP_FILE_SHARED
* properly (dcache readdir is still enabled) */
di = ceph_dentry(dentry);
if (di->offset > 0 &&
di->lease_shared_gen == atomic_read(&dir_ci->i_shared_gen))
__ceph_dir_clear_ordered(dir_ci);
}
/*

38
fs/ceph/inode.c
View file

@ -1080,6 +1080,27 @@ static struct dentry *splice_dentry(struct dentry *dn, struct inode *in)
BUG_ON(d_inode(dn));
if (S_ISDIR(in->i_mode)) {
/* If inode is directory, d_splice_alias() below will remove
* 'realdn' from its origin parent. We need to ensure that
* origin parent's readdir cache will not reference 'realdn'
*/
realdn = d_find_any_alias(in);
if (realdn) {
struct ceph_dentry_info *di = ceph_dentry(realdn);
spin_lock(&realdn->d_lock);
realdn->d_op->d_prune(realdn);
di->time = jiffies;
di->lease_shared_gen = 0;
di->offset = 0;
spin_unlock(&realdn->d_lock);
dput(realdn);
}
}
/* dn must be unhashed */
if (!d_unhashed(dn))
d_drop(dn);
@ -1295,8 +1316,8 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
if (!rinfo->head->is_target) {
dout("fill_trace null dentry\n");
if (d_really_is_positive(dn)) {
ceph_dir_clear_ordered(dir);
dout("d_delete %p\n", dn);
ceph_dir_clear_ordered(dir);
d_delete(dn);
} else if (have_lease) {
if (d_unhashed(dn))
@ -1323,7 +1344,6 @@ int ceph_fill_trace(struct super_block *sb, struct ceph_mds_request *req)
dout(" %p links to %p %llx.%llx, not %llx.%llx\n",
dn, d_inode(dn), ceph_vinop(d_inode(dn)),
ceph_vinop(in));
ceph_dir_clear_ordered(dir);
d_invalidate(dn);
have_lease = false;
}
@ -1573,9 +1593,19 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
} else if (d_really_is_positive(dn) &&
(ceph_ino(d_inode(dn)) != tvino.ino ||
ceph_snap(d_inode(dn)) != tvino.snap)) {
struct ceph_dentry_info *di = ceph_dentry(dn);
dout(" dn %p points to wrong inode %p\n",
dn, d_inode(dn));
spin_lock(&dn->d_lock);
if (di->offset > 0 &&
di->lease_shared_gen ==
atomic_read(&ci->i_shared_gen)) {
__ceph_dir_clear_ordered(ci);
di->offset = 0;
}
spin_unlock(&dn->d_lock);
d_delete(dn);
dput(dn);
goto retry_lookup;
@ -1600,9 +1630,7 @@ int ceph_readdir_prepopulate(struct ceph_mds_request *req,
&req->r_caps_reservation);
if (ret < 0) {
pr_err("fill_inode badness on %p\n", in);
if (d_really_is_positive(dn))
__ceph_dir_clear_ordered(ci);
else
if (d_really_is_negative(dn))
iput(in);
d_drop(dn);
err = ret;