diff options
| author | Vivek Goyal <vgoyal@redhat.com> | 2020-10-09 14:15:10 -0400 |
|---|---|---|
| committer | Miklos Szeredi <mszeredi@redhat.com> | 2020-11-11 17:22:33 +0100 |
| commit | 8981bdfda7445af5d5a8c277c923bf91873a0c98 (patch) | |
| tree | 4b302bf7f4d2b2d1bafc1bb63cee1e538cefb30e /fs/fuse | |
| parent | 3179216135ec09825d7c7875580951a6e69dc5df (diff) | |
fuse: don't send ATTR_MODE to kill suid/sgid for handle_killpriv_v2
If client does a write() on a suid/sgid file, VFS will first call
fuse_setattr() with ATTR_KILL_S[UG]ID set. This requires sending setattr
to file server with ATTR_MODE set to kill suid/sgid. But to do that client
needs to know latest mode otherwise it is racy.
To reduce the race window, current code first call fuse_do_getattr() to get
latest ->i_mode and then resets suid/sgid bits and sends rest to server
with setattr(ATTR_MODE). This does not reduce the race completely but
narrows race window significantly.
With fc->handle_killpriv_v2 enabled, it should be possible to remove this
race completely. Do not kill suid/sgid with ATTR_MODE at all. It will be
killed by server when WRITE request is sent to server soon. This is
similar to fc->handle_killpriv logic. V2 is just more refined version of
protocol. Hence this patch does not send ATTR_MODE to kill suid/sgid if
fc->handle_killpriv_v2 is enabled.
This creates an issue if fc->writeback_cache is enabled. In that case
WRITE can be cached in guest and server might not see WRITE request and
hence will not kill suid/sgid. Miklos suggested that in such cases, we
should fallback to a writethrough WRITE instead and that will generate
WRITE request and kill suid/sgid. This patch implements that too.
But this relies on client seeing the suid/sgid set. If another client sets
suid/sgid and this client does not see it immideately, then we will not
fallback to writethrough WRITE. So this is one limitation with both
fc->handle_killpriv_v2 and fc->writeback_cache enabled. Both the options
are not fully compatible. But might be good enough for many use cases.
Note: This patch is not checking whether security.capability is set or not
when falling back to writethrough path. If suid/sgid is not set and
only security.capability is set, that will be taken care of by
file_remove_privs() call in ->writeback_cache path.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/fuse')
| -rw-r--r-- | fs/fuse/dir.c | 2 | ||||
| -rw-r--r-- | fs/fuse/file.c | 9 |
2 files changed, 9 insertions, 2 deletions
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c index 28b07ae5e55f..778367d125f9 100644 --- a/fs/fuse/dir.c +++ b/fs/fuse/dir.c @@ -1749,7 +1749,7 @@ static int fuse_setattr(struct dentry *entry, struct iattr *attr) * * This should be done on write(), truncate() and chown(). */ - if (!fc->handle_killpriv) { + if (!fc->handle_killpriv && !fc->handle_killpriv_v2) { /* * ia_mode calculation may have used stale i_mode. * Refresh and recalculate. diff --git a/fs/fuse/file.c b/fs/fuse/file.c index 24b201c4d9a9..aa0a44f7028f 100644 --- a/fs/fuse/file.c +++ b/fs/fuse/file.c @@ -1262,17 +1262,24 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from) ssize_t written_buffered = 0; struct inode *inode = mapping->host; ssize_t err; + struct fuse_conn *fc = get_fuse_conn(inode); loff_t endbyte = 0; - if (get_fuse_conn(inode)->writeback_cache) { + if (fc->writeback_cache) { /* Update size (EOF optimization) and mode (SUID clearing) */ err = fuse_update_attributes(mapping->host, file); if (err) return err; + if (fc->handle_killpriv_v2 && + should_remove_suid(file_dentry(file))) { + goto writethrough; + } + return generic_file_write_iter(iocb, from); } +writethrough: inode_lock(inode); /* We can write back this queue in page reclaim */ |