On Wed, Oct 22, 2014 at 7:44 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Wed, Oct 22, 2014 at 4:44 AM, David Drysdale <drysdale@xxxxxxxxxx> wrote:
>> Add a new system execveat(2) syscall. execveat() is to execve() as
>> openat() is to open(): it takes a file descriptor that refers to a
>> directory, and resolves the filename relative to that.
>>
>
>> bprm->file = file;
>> - bprm->filename = bprm->interp = filename->name;
>> + if (fd == AT_FDCWD || filename->name[0] == '/') {
>> + bprm->filename = filename->name;
>> + } else {
>> + /*
>> + * Build a pathname that reflects how we got to the file,
>> + * either "/dev/fd/<fd>" (for an empty filename) or
>> + * "/dev/fd/<fd>/<filename>".
>> + */
>> + pathbuf = kmalloc(PATH_MAX, GFP_TEMPORARY);
>> + if (!pathbuf) {
>> + retval = -ENOMEM;
>> + goto out_unmark;
>> + }
>> + bprm->filename = pathbuf;
>> + if (filename->name[0] == '\0')
>> + sprintf(pathbuf, "/dev/fd/%d", fd);
>
> If the fd is O_CLOEXEC, then this will result in a confused child
> process. Should we fail exec attempts like that for non-static
> programs? (E.g. set filename to "" or something and fix up the binfmt
> drivers to handle that?)
Isn't it just scripts that get confused here (as normal executables don't
get to see brpm->filename)?
Given that we don't know which we have at this point, I'd suggest
carrying on regardless. Or we could fall back to use the previous
best-effort d_path() code for O_CLOEXEC fds. Thoughts?
>> + else
>> + snprintf(pathbuf, PATH_MAX,
>> + "/dev/fd/%d/%s", fd, filename->name);
>
> Does this need to handle the case where the result exceeds PATH_MAX?
I guess we could kmalloc(strlen(filename->name) + 19) to avoid the
possibility of failure, but that just defers the inevitable -- the interpreter
won't be able to open the script file anyway. But it would at least then
generate the appropriate error (ENAMETOOLONG rather than ENOENT).
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