Re: [RFC PATCH] ceph: allow encrypting a directory while not having Ax caps
From: Xiubo Li
Date: Wed Nov 02 2022 - 23:20:05 EST
On 02/11/2022 19:48, Luís Henriques wrote:
On Mon, Oct 31, 2022 at 05:15:51PM +0800, Xiubo Li wrote:
On 27/10/2022 19:26, Luís Henriques wrote:
If a client doesn't have Fx caps on a directory, it will get errors while
trying encrypt it:
ceph: handle_cap_grant: cap grant attempt to change fscrypt_auth on non-I_NEW inode (old len 0 new len 48)
fscrypt (ceph, inode 1099511627812): Error -105 getting encryption context
A simple way to reproduce this is to use two clients:
client1 # mkdir /mnt/mydir
client2 # ls /mnt/mydir
client1 # fscrypt encrypt /mnt/mydir
client1 # echo hello > /mnt/mydir/world
This happens because, in __ceph_setattr(), we only initialize
ci->fscrypt_auth if we have Ax. If we don't have, we'll need to do that
later, in handle_cap_grant().
Signed-off-by: Luís Henriques <lhenriques@xxxxxxx>
---
Hi!
To be honest, I'm not really sure about the conditions in the 'if': shall
I bother checking it's really a dir and that it is empty?
Cheers,
--
Luís
fs/ceph/caps.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 443fce066d42..e33b5c276cf3 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -3511,9 +3511,29 @@ static void handle_cap_grant(struct inode *inode,
from_kuid(&init_user_ns, inode->i_uid),
from_kgid(&init_user_ns, inode->i_gid));
#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
- if (ci->fscrypt_auth_len != extra_info->fscrypt_auth_len ||
- memcmp(ci->fscrypt_auth, extra_info->fscrypt_auth,
- ci->fscrypt_auth_len))
+ if ((ci->fscrypt_auth_len == 0) &&
+ (extra_info->fscrypt_auth_len > 0) &&
+ S_ISDIR(inode->i_mode) &&
+ (ci->i_rsubdirs + ci->i_rfiles == 1)) {
+ /*
+ * We'll get here when setting up an encrypted directory
+ * but we don't have Fx in that directory, i.e. other
+ * clients have accessed this directory too.
+ */
+ ci->fscrypt_auth = kmemdup(extra_info->fscrypt_auth,
+ extra_info->fscrypt_auth_len,
+ GFP_KERNEL);
+ if (ci->fscrypt_auth) {
+ inode->i_flags |= S_ENCRYPTED;
+ ci->fscrypt_auth_len = extra_info->fscrypt_auth_len;
+ } else {
+ pr_err("Failed to alloc memory for %llx.%llx fscrypt_auth\n",
+ ceph_vinop(inode));
+ }
+ dout("ino %llx.%llx is now encrypted\n", ceph_vinop(inode));
+ } else if (ci->fscrypt_auth_len != extra_info->fscrypt_auth_len ||
+ memcmp(ci->fscrypt_auth, extra_info->fscrypt_auth,
+ ci->fscrypt_auth_len))
pr_warn_ratelimited("%s: cap grant attempt to change fscrypt_auth on non-I_NEW inode (old len %d new len %d)\n",
__func__, ci->fscrypt_auth_len, extra_info->fscrypt_auth_len);
#endif
Hi Luis,
Thanks for your time on this bug.
IMO we should fix this in ceph_fill_inode():
995 #ifdef CONFIG_FS_ENCRYPTION
996 if (iinfo->fscrypt_auth_len && (inode->i_state & I_NEW)) {
997 kfree(ci->fscrypt_auth);
998 ci->fscrypt_auth_len = iinfo->fscrypt_auth_len;
999 ci->fscrypt_auth = iinfo->fscrypt_auth;
1000 iinfo->fscrypt_auth = NULL;
1001 iinfo->fscrypt_auth_len = 0;
1002 inode_set_flags(inode, S_ENCRYPTED, S_ENCRYPTED);
1003 }
1004 #endif
The setattr will get a reply from MDS including the fscrypt auth info, I
think the kclient just drop it here.
I've done some testing and I don't really see this code kfree'ing a valid
fscrypt_auth here. However, I guess it is possible to fix this issue here
too, but in a different way, by changing that 'if' condition to:
if (iinfo->fscrypt_auth_len &&
((inode->i_state & I_NEW) || (ci->fscrypt_auth_len == 0))) {
...
}
I'm not really sure if this is sane though. When we loose the 'Ax' caps
(another client as accessed the directory we're encrypting), we also seem
to loose the I_NEW state. Using the above code seems to work for the
testcase in my patch, but I'm not sure it won't break something else.
It should be okay IMO.
The I_NEW is for new created directories, such as for mkdir request,etc.
But currently the code didn't consider the setattr case.
Please send you patch let's check and discuss there.
Thanks!
- Xiubo
Cheers,
--
Luís
If we fix it in handle_cap_grant() I am afraid this bug still exists. What
if there is no any new caps will be issued or revoked recently and then
access to the directory ?
Thanks
- Xiubo