On Tue, 24 Oct 2006, Maxim Sobolev wrote:
sobomax 2006-10-24 08:18:10 UTC
FreeBSD src repository
Modified files:
usr.bin/su su.c
Log:
Ignore SIGSYS when BSM is compiled in. Otherwise, attempt to invoke su on
system that don't have audit framefork compiled into kernel or ia32
binary
on amd64 system will result in SIGSYS. There is one place in su.c itself
where it tries to check for errno != ENOSYS, but it has been a nop since
su
does not catch SIGSYS anyway. There are few other places in libbsm,
where attempt to invoke audit syscal would result in SIGSYS if no audit
support is present in the kernel, so that the only reliable method for
now is to disable SIGSYS completely in the case when BSM is compiled in.
In the long run, both direct invocation of audit-related syscalls and
libbsm should be made more intellegent to handle the case when BSM is not
compiled into the kernel gracefully.
MFC after: 3 days
(provided re@ approval)
I have to admit being a bit puzzled by your commit. Since you didn't
bother to contact me with a bug report before committing this presumed fix,
I can only assume that you are entirely certain that what you're describing
is the case. However, since it appears not to be the case on thousands of
deployed HEAD and RELENG_6 machines, I have to wonder whether you're
hitting an edge case that needs further debugging and discussion.
Alternatively, you booted a really old kernel with a relatively new user
space. And by really old, I mean RELENG_6 in March of this year, or HEAD
in February. How did you manage to log in, as login(1) also invokes the
same system calls unconditionally that su(1) calls? Returning ENOSYS from
a system call stub should not (and in my experience, does not) generate
SIGSYS. There are three common cases for unimplemented system calls:
(1) The kernel doesn't recognize the system call. Return ENOSYS + SIGSYS.
If
a binary handles SIGSYS, it gets the ENOSYS return, otherwise, it
exits.
This occurs if the system call isn't listed in the system call table,
or
if it's listed but unimplemented. This is what happens if you invoke a
random system call number, or a new system call on a really old kernel.
(2) The kernel recognizes, but does not implement the system call, and the
system call is one where error handling is possible. This occurs when
a
system call stub function returns ENOSYS. For example, the audit code
contains conditionally compiled system call code that returns ENOSYS if
AUDIT isn't in the kernel. This also occurs when compatibility stubs
are
inserted to allow forward compatibility.
(3) The kernel recognizes and implements the system call, but the
underlying
object doesn't implement the call. Return EOPNOTSUPP, ENOTSUP, EINVAL,
etc. Typical examples are VFS system calls where the file system
doesn't
implement the operation, such as extended attributes, hard links, etc.
The audit subsystem uses the second approach so that userland binaries can
detect that audit is not available and handle it properly (typically by not
configuring audit and generating audit events). Notice that we merged
audit system call stubs to RELENG_6 for 6.1-RELEASE so that the upgrade
path to an audit-enabled userland in 6.2-RELEASE would be un-bumpy if the
user didn't properly follow proper upgrade instructions (kernel before user
space).
So: could you confirm that what you're observing is happening and provide
specific specific debugging information? For example, your commit message
hand-waves at 32-bit binaries on amd64 -- perhaps there is a bug in the
handling of ENOSYS in the compat/freebsd32 system call path. A casual
reading of the system call code suggests that this is not the case, but I
don't think this is a case I have specifically tested. If you're running a
very old kernel (pre-February/March) with a new user space, understand that
that is not a supported configuration that will break for other more subtle
reasons, and please back out this commit.
Thanks,
Robert N M Watson
Computer Laboratory
University of Cambridge
