[Virtio-fs] [PATCH v2 4/6] fuse: Kill suid/sgid using ATTR_MODE if it is not truncate
Vivek Goyal
vgoyal at redhat.com
Wed Sep 16 16:17:35 UTC 2020
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 <vgoyal at redhat.com>
---
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
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