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virtiofsd: Disable killpriv_v2 by default 

We are having bunch of issues with killpriv_v2 enabled by default. First
of all it relies on clearing suid/sgid bits as needed by dropping
capability CAP_FSETID. This does not work for remote filesystems like
NFS (and possibly others).

Secondly, we are noticing other issues related to clearing of SGID
which leads to failures for xfstests generic/355 and generic/193.

Thirdly, there are other issues w.r.t caching of metadata (suid/sgid)
bits in fuse client with killpriv_v2 enabled. Guest can cache that
data for sometime even if cleared on server.

Second and Third issue are fixable. Just that it might take a little
while to get it fixed in kernel. First one will probably not see
any movement for a long time.

Given these issues, killpriv_v2 does not seem to be a good candidate
for enabling by default. We have already disabled it by default in
rust version of virtiofsd.

Hence this patch disabled killpriv_v2 by default. User can choose to
enable it by passing option "-o killpriv_v2".

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Message-Id: <YuPd0itNIAz4tQRt@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Vivek Goyal 2022-07-29 09:17:06 -04:00 committed by Dr. David Alan Gilbert
parent 4bcb7de072
commit a21ba54dd5
1 changed files with 2 additions and 11 deletions
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13
tools/virtiofsd/passthrough_ll.c
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@ -767,19 +767,10 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n");
conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2;
lo->killpriv_v2 = 1;
} else if (lo->user_killpriv_v2 == -1 &&
conn->capable & FUSE_CAP_HANDLE_KILLPRIV_V2) {
/*
* User did not specify a value for killpriv_v2. By default enable it
* if connection offers this capability
*/
fuse_log(FUSE_LOG_DEBUG, "lo_init: enabling killpriv_v2\n");
conn->want |= FUSE_CAP_HANDLE_KILLPRIV_V2;
lo->killpriv_v2 = 1;
} else {
/*
* Either user specified to disable killpriv_v2, or connection does
* not offer this capability. Disable killpriv_v2 in both the cases
* Either user specified to disable killpriv_v2, or did not
* specify anything. Disable killpriv_v2 in both the cases.
*/
fuse_log(FUSE_LOG_DEBUG, "lo_init: disabling killpriv_v2\n");
conn->want &= ~FUSE_CAP_HANDLE_KILLPRIV_V2;