do_filp_open fails to detect dentry revalidate of 1 and crashes

do_filp_open fails to detect dentry revalidate of 1 and crashes

[jmerkey]

On assignment of a negative dentry, do_filp_open will crash with an oops
in do_sys_open because do_filp_open returns "1" from revalidate rather
than properly detect a negative dentry which has a dentry revalidate
function before the file actually exists.


Easy to reproduce.  Create negative dentry and attach a revalidate
function which returns 1 instead of 0 on non-existent file entry.   The
convoluted code in do_filp_open does not detect dentry errors in all cases
properly.

Jeff

Re: do_filp_open fails to detect dentry revalidate of 1 and crashes

[jmerkey]

>
> On assignment of a negative dentry, do_filp_open will crash with an oops
> in do_sys_open because do_filp_open returns "1" from revalidate rather
> than properly detect a negative dentry which has a dentry revalidate
> function before the file actually exists.
>
>
> Easy to reproduce.  Create negative dentry and attach a revalidate
> function which returns 1 instead of 0 on non-existent file entry.   The
> convoluted code in do_filp_open does not detect dentry errors in all cases
> properly.
>
> Jeff
>

Correction:

It's vfs_create that fails to check return codes properly.

        /*
         * Create - we need to know the parent.
         */
        error = path_lookup_create(dfd, pathname, LOOKUP_PARENT,
                                   &nd, flag, mode);


////
If ERROR is a positive value, ERR_PTR fails to convert it to a negative
value.  This causes the EDI register to get set to "1" after do_filp_open
returns.

////

        if (error)
                return ERR_PTR(error);



        /*
         * We have the parent and last component. First of all, check
         * that we are not asked to creat(2) an obvious directory - that
         * will not do.
         */
        error = -EISDIR;
        if (nd.last_type != LAST_NORM || nd.last.name[nd.last.len])
                goto exit;