If a truncate is happening with ->handle_killpriv_v2 is enabled, then we don't have to send ATTR_MODE to kill suid/sgid as server will kill it as part of the protocol.
But if this is non-truncate setattr then server will not kill suid/sgid. So continue to send ATTR_MODE to kill suid/sgid for non-truncate setattr, even if ->handle_killpriv_v2 is enabled. This path is taken when client does a write on a file which has suid/ sgid is set. VFS will first kill suid/sgid and then proceed with WRITE. One can argue that why not simply ignore ATTR_MODE because a WRITE will follow and ->handle_killpriv_v2 will kill suid/sgid that time. I feel this is a safer approach for following reasons. - With ->writeback_cache enabled, WRITE will not go to server. I feel that for this reason ->writeback_cache mode is not fully compatible with ->handle_killpriv_v2. But if we kill suid/sgid now, this will solve this particular issue for ->writeback_cache mode too. Again, I will not solve all the issues around ->writeback_cache but makes things better. - If we rely on WRITE killing suid/sgid, then after cache becomes out of sync w.r.t host. Client will still have suid/sgid set but subsequent WRITE will clear suid/sgid. Well WRITE will also invalidate client cache so further access to inode->i_mode should result in a ->getattr. Hmm..., for the case of ->writeback_cache, I am kind of inclined to send ATTR_MODE. - We are sending setattr(ATTR_FORCE) anyway (even if we clear ATTR_MODE). So if we are not saving on setattr(), why not kill suid/sgid now. Signed-off-by: Vivek Goyal <[email protected]> --- fs/fuse/dir.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index ecdb7895c156..4b0fe0828e36 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -1655,6 +1655,21 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr) return -EACCES; if (attr->ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID)) { + bool kill_sugid = true; + bool is_truncate = !!(attr->ia_valid & ATTR_SIZE); + + if (fc->handle_killpriv || + (fc->handle_killpriv_v2 && is_truncate)) { + /* + * If this is truncate and ->handle_killpriv_v2 is + * enabled, we don't have to send ATTR_MODE to + * kill suid/sgid as server will do it anyway as + * part of truncate. But if this is not truncate + * then kill suid/sgid by sending ATTR_MODE. + */ + kill_sugid = false; + } + attr->ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID | ATTR_MODE); @@ -1664,7 +1679,7 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr) * * This should be done on write(), truncate() and chown(). */ - if (!fc->handle_killpriv) { + if (kill_sugid) { /* * ia_mode calculation may have used stale i_mode. * Refresh and recalculate. -- 2.25.4 _______________________________________________ Virtio-fs mailing list [email protected] https://www.redhat.com/mailman/listinfo/virtio-fs
