Dan Carpenter <dan.carpenter@xxxxxxxxxx> writes:
> Hello Eric W. Biederman,
>
> This is a semi-automatic email about new static checker warnings.
>
> The patch 4ce5d2b1a8fd: "vfs: Don't copy mount bind mounts of
> /proc/<pid>/ns/mnt between namespaces" from Mar 30, 2013, leads to
> the following Smatch complaint:
Semi-autoautomatic reply. The test !q is enough to ensure p is valid
until p->mnt.mnt_root == q->mnt.mnt_root.
This has been verified through both testing and reading of the code.
Eric
> fs/namespace.c:2459 dup_mnt_ns()
> warn: variable dereferenced before check 'p' (see line 2475)
>
> fs/namespace.c
> 2441 new = copy_tree(old, old->mnt.mnt_root, copy_flags);
> ^^^^^^^^^^^^^^^^^
> Old is dereferenced.
>
> 2442 if (IS_ERR(new)) {
> 2443 namespace_unlock();
> 2444 free_mnt_ns(new_ns);
> 2445 return ERR_CAST(new);
> 2446 }
> 2447 new_ns->root = new;
> 2448 br_write_lock(&vfsmount_lock);
> 2449 list_add_tail(&new_ns->list, &new->mnt_list);
> 2450 br_write_unlock(&vfsmount_lock);
> 2451
> 2452 /*
> 2453 * Second pass: switch the tsk->fs->* elements and mark new vfsmounts
> 2454 * as belonging to new namespace. We have already acquired a private
> 2455 * fs_struct, so tsk->fs->lock is not needed.
> 2456 */
> 2457 p = old;
> ^^^^^^^
>
> P is a valid pointer.
>
> 2458 q = new;
> 2459 while (p) {
> ^^^
> Existing check for "p".
>
> 2460 q->mnt_ns = new_ns;
> 2461 if (fs) {
> 2462 if (&p->mnt == fs->root.mnt) {
> 2463 fs->root.mnt = mntget(&q->mnt);
> 2464 rootmnt = &p->mnt;
> 2465 }
> 2466 if (&p->mnt == fs->pwd.mnt) {
> 2467 fs->pwd.mnt = mntget(&q->mnt);
> 2468 pwdmnt = &p->mnt;
> 2469 }
> 2470 }
> 2471 p = next_mnt(p, old);
> 2472 q = next_mnt(q, new);
> 2473 if (!q)
> 2474 break;
> 2475 while (p->mnt.mnt_root != q->mnt.mnt_root)
> ^^^^^^^^^^^^^^^
> We dereference "p".
>
> 2476 p = next_mnt(p, old);
> 2477 }
>
> regards,
> dan carpenter
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