ceph: fix overflowed value issue in ceph_submit_write()

The Coverity Scan service has detected overflowed value
issue in ceph_submit_write() [1]. The CID 1646339 defect
contains explanation: "The overflowed value due to
arithmetic on constants is too small or unexpectedly
negative, causing incorrect computations.
In ceph_submit_write: Integer overflow occurs in
arithmetic on constant operands (CWE-190)".

This patch adds a check ceph_wbc->locked_pages on
equality to zero and it exits function if it has
zero value. Also, it introduces a processed_pages
variable with the goal of assigning the number of
processed pages and checking this number on
equality to zero. The check of processed_pages
variable on equality to zero should protect from
overflowed value of index that selects page in
ceph_wbc->pages[index] array.

[1] https://scan5.scan.coverity.com/#/project-view/64304/10063?selectedIssue=1646339

Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>

diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 5a5751156f8bf45cd5c1a8458d6aabc164e278f4..a4ffa2b631841fcec3ba60de74ed32bf585083be 100644 (file)
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1418,6 +1418,7 @@ int ceph_submit_write(struct address_space *mapping,
        bool caching = ceph_is_cache_enabled(inode);
        u64 offset;
        u64 len;
+       unsigned processed_pages;
        unsigned i;
 
 new_request:
@@ -1445,6 +1446,9 @@ new_request:
                BUG_ON(IS_ERR(req));
        }
 
+       if (ceph_wbc->locked_pages == 0)
+               return -EINVAL;
+
        page = ceph_wbc->pages[ceph_wbc->locked_pages - 1];
        BUG_ON(len < ceph_fscrypt_page_offset(page) + thp_size(page) - offset);
 
@@ -1481,6 +1485,7 @@ new_request:
        len = 0;
        ceph_wbc->data_pages = ceph_wbc->pages;
        ceph_wbc->op_idx = 0;
+       processed_pages = 0;
        for (i = 0; i < ceph_wbc->locked_pages; i++) {
                u64 cur_offset;
 
@@ -1524,19 +1529,22 @@ new_request:
                        ceph_set_page_fscache(page);
 
                len += thp_size(page);
+               processed_pages++;
        }
 
        ceph_fscache_write_to_cache(inode, offset, len, caching);
 
        if (ceph_wbc->size_stable) {
                len = min(len, ceph_wbc->i_size - offset);
-       } else if (i == ceph_wbc->locked_pages) {
+       } else if (processed_pages > 0 &&
+                  processed_pages == ceph_wbc->locked_pages) {
                /* writepages_finish() clears writeback pages
                 * according to the data length, so make sure
                 * data length covers all locked pages */
                u64 min_len = len + 1 - thp_size(page);
+               unsigned index = processed_pages - 1;
                len = get_writepages_data_length(inode,
-                                                ceph_wbc->pages[i - 1],
+                                                ceph_wbc->pages[index],
                                                 offset);
                len = max(len, min_len);
        }
@@ -1561,17 +1569,17 @@ new_request:
        BUG_ON(ceph_wbc->op_idx + 1 != req->r_num_ops);
 
        ceph_wbc->from_pool = false;
-       if (i < ceph_wbc->locked_pages) {
+       if (processed_pages < ceph_wbc->locked_pages) {
                BUG_ON(ceph_wbc->num_ops <= req->r_num_ops);
                ceph_wbc->num_ops -= req->r_num_ops;
-               ceph_wbc->locked_pages -= i;
+               ceph_wbc->locked_pages -= processed_pages;
 
                /* allocate new pages array for next request */
                ceph_wbc->data_pages = ceph_wbc->pages;
                __ceph_allocate_page_array(ceph_wbc, ceph_wbc->locked_pages);
-               memcpy(ceph_wbc->pages, ceph_wbc->data_pages + i,
+               memcpy(ceph_wbc->pages, ceph_wbc->data_pages + processed_pages,
                        ceph_wbc->locked_pages * sizeof(*ceph_wbc->pages));
-               memset(ceph_wbc->data_pages + i, 0,
+               memset(ceph_wbc->data_pages + processed_pages, 0,
                        ceph_wbc->locked_pages * sizeof(*ceph_wbc->pages));
        } else {
                BUG_ON(ceph_wbc->num_ops != req->r_num_ops);
@@ -1583,7 +1591,7 @@ new_request:
        ceph_osdc_start_request(&fsc->client->osdc, req);
        req = NULL;
 
-       wbc->nr_to_write -= i;
+       wbc->nr_to_write -= processed_pages;
        if (ceph_wbc->pages)
                goto new_request;