ceph: fix potential race condition in ceph_ioctl_lazyio()

The Coverity Scan service has detected potential
race condition in ceph_ioctl_lazyio() [1].

The CID 1591046 contains explanation: "Check of thread-shared
field evades lock acquisition (LOCK_EVASION). Thread1 sets
fmode to a new value. Now the two threads have an inconsistent
view of fmode and updates to fields correlated with fmode
may be lost. The data guarded by this critical section may
be read while in an inconsistent state or modified by multiple
racing threads. In ceph_ioctl_lazyio: Checking the value of
a thread-shared field outside of a locked region to determine
if a locked operation involving that thread shared field
has completed. (CWE-543)".

The patch places fi->fmode field access under ci->i_ceph_lock
protection. Also, it introduces the is_file_already_lazy
variable that is set under the lock and it is checked later
out of scope of critical section.

[1] https://scan5.scan.coverity.com/#/project-view/64304/10063?selectedIssue=1591046

Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/fs/ceph/ioctl.c b/fs/ceph/ioctl.c
index e861de3c79b9e126849d930500dee51aff072c80..15cde055f3da13e2daf682d6f8e189700b303500 100644 (file)
--- a/fs/ceph/ioctl.c
+++ b/fs/ceph/ioctl.c
@@ -246,21 +246,28 @@ static long ceph_ioctl_lazyio(struct file *file)
        struct ceph_inode_info *ci = ceph_inode(inode);
        struct ceph_mds_client *mdsc = ceph_inode_to_fs_client(inode)->mdsc;
        struct ceph_client *cl = mdsc->fsc->client;
+       bool is_file_already_lazy = false;
 
+       spin_lock(&ci->i_ceph_lock);
        if ((fi->fmode & CEPH_FILE_MODE_LAZY) == 0) {
-               spin_lock(&ci->i_ceph_lock);
                fi->fmode |= CEPH_FILE_MODE_LAZY;
                ci->i_nr_by_mode[ffs(CEPH_FILE_MODE_LAZY)]++;
                __ceph_touch_fmode(ci, mdsc, fi->fmode);
-               spin_unlock(&ci->i_ceph_lock);
+       } else {
+               is_file_already_lazy = true;
+       }
+       spin_unlock(&ci->i_ceph_lock);
+
+       if (is_file_already_lazy) {
+               doutc(cl, "file %p %p %llx.%llx already lazy\n", file, inode,
+                     ceph_vinop(inode));
+       } else {
                doutc(cl, "file %p %p %llx.%llx marked lazy\n", file, inode,
                      ceph_vinop(inode));
 
                ceph_check_caps(ci, 0);
-       } else {
-               doutc(cl, "file %p %p %llx.%llx already lazy\n", file, inode,
-                     ceph_vinop(inode));
        }
+
        return 0;
 }