From 5495c2d04f85da09512f5f346ed24dc0261d905d Mon Sep 17 00:00:00 2001 From: "Yan, Zheng" Date: Mon, 27 Nov 2017 11:23:48 +0800 Subject: [PATCH] ceph: avoid dereferencing invalid pointer during cached readdir 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" Acked-by: Jeff Layton Signed-off-by: Ilya Dryomov --- fs/ceph/dir.c | 45 ++++++++++++++++++++++++++++++++------------- fs/ceph/inode.c | 40 ++++++++++++++++++++++++++++++++++------ 2 files changed, 66 insertions(+), 19 deletions(-) diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c index d671d5876828..0c4346806e17 100644 --- a/fs/ceph/dir.c +++ b/fs/ceph/dir.c @@ -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); } /* diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c index 6d02528eb61f..c6ec5aa46100 100644 --- a/fs/ceph/inode.c +++ b/fs/ceph/inode.c @@ -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)); - __ceph_dir_clear_ordered(ci); + + 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; -- GitLab