From 2105c2820d366b76f38e6ad61c75771881ecc532 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 10 Apr 2020 15:23:27 +0100 Subject: afs: Fix race between post-modification dir edit and readdir/d_revalidate AFS directories are retained locally as a structured file, with lookup being effected by a local search of the file contents. When a modification (such as mkdir) happens, the dir file content is modified locally rather than redownloading the directory. The directory contents are accessed in a number of ways, with a number of different locks schemes: (1) Download of contents - dvnode->validate_lock/write in afs_read_dir(). (2) Lookup and readdir - dvnode->validate_lock/read in afs_dir_iterate(), downgrading from (1) if necessary. (3) d_revalidate of child dentry - dvnode->validate_lock/read in afs_do_lookup_one() downgrading from (1) if necessary. (4) Edit of dir after modification - page locks on individual dir pages. Unfortunately, because (4) uses different locking scheme to (1) - (3), nothing protects against the page being scanned whilst the edit is underway. Even download is not safe as it doesn't lock the pages - relying instead on the validate_lock to serialise as a whole (the theory being that directory contents are treated as a block and always downloaded as a block). Fix this by write-locking dvnode->validate_lock around the edits. Care must be taken in the rename case as there may be two different dirs - but they need not be locked at the same time. In any case, once the lock is taken, the directory version must be rechecked, and the edit skipped if a later version has been downloaded by revalidation (there can't have been any local changes because the VFS holds the inode lock, but there can have been remote changes). Fixes: 63a4681ff39c ("afs: Locally edit directory data for mkdir/create/unlink/...") Signed-off-by: David Howells --- fs/afs/dir_silly.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) (limited to 'fs/afs/dir_silly.c') diff --git a/fs/afs/dir_silly.c b/fs/afs/dir_silly.c index 361088a5edb9..d94e2b7cddff 100644 --- a/fs/afs/dir_silly.c +++ b/fs/afs/dir_silly.c @@ -21,6 +21,7 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode { struct afs_fs_cursor fc; struct afs_status_cb *scb; + afs_dataversion_t dir_data_version; int ret = -ERESTARTSYS; _enter("%pd,%pd", old, new); @@ -31,7 +32,7 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode trace_afs_silly_rename(vnode, false); if (afs_begin_vnode_operation(&fc, dvnode, key, true)) { - afs_dataversion_t dir_data_version = dvnode->status.data_version + 1; + dir_data_version = dvnode->status.data_version + 1; while (afs_select_fileserver(&fc)) { fc.cb_break = afs_calc_vnode_cb_break(dvnode); @@ -54,12 +55,15 @@ static int afs_do_silly_rename(struct afs_vnode *dvnode, struct afs_vnode *vnode dvnode->silly_key = key_get(key); } - if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags)) + down_write(&dvnode->validate_lock); + if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags) && + dvnode->status.data_version == dir_data_version) { afs_edit_dir_remove(dvnode, &old->d_name, afs_edit_dir_for_silly_0); - if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags)) afs_edit_dir_add(dvnode, &new->d_name, &vnode->fid, afs_edit_dir_for_silly_1); + } + up_write(&dvnode->validate_lock); } kfree(scb); @@ -181,10 +185,14 @@ static int afs_do_silly_unlink(struct afs_vnode *dvnode, struct afs_vnode *vnode clear_bit(AFS_VNODE_CB_PROMISED, &vnode->flags); } } - if (ret == 0 && - test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags)) - afs_edit_dir_remove(dvnode, &dentry->d_name, - afs_edit_dir_for_unlink); + if (ret == 0) { + down_write(&dvnode->validate_lock); + if (test_bit(AFS_VNODE_DIR_VALID, &dvnode->flags) && + dvnode->status.data_version == dir_data_version) + afs_edit_dir_remove(dvnode, &dentry->d_name, + afs_edit_dir_for_unlink); + up_write(&dvnode->validate_lock); + } } kfree(scb); -- cgit v1.2.3