On 12/21/2017 06:18 AM, Tom Horsley wrote:
On my fedora 26 box with a 4.13 kernel, when a process
under ptrace control did an exec of a setuid program,
the program lost all of its setuid privileges and
ptrace could operate on it like a normal program.
Experimental evidence seems to indicate that on
fedora 27 with a 4.14 kernel, ptrace cannot
do a PEEKDATA to read anything from the just
execed setuid program. (I get errno 5 - I/O error).
Am I confused somehow, or did something really change
in this vicinity?
It puts a real crimp in my fancy debug feature to
patch code into a setuid program to make it re-exec itself,
then detach from it. (I don't suppose we could get
a setoptions feature to tell the kernel to detach
from setuid programs automagically and let the debugger
know it is no longer in control of the process?)
Assuming this is https://bugzilla.redhat.com/show_bug.cgi?id=1528633
This is yet another victim of
commit e37fdb785a5f95ecadf43b773c97f676500ac7b8 (refs/bisect/bad)
Author: Kees Cook <[email protected]>
Date: Tue Jul 18 15:25:31 2017 -0700
exec: Use secureexec for setting dumpability
The examination of "current" to decide dumpability is wrong. This was a
check of and euid/uid (or egid/gid) mismatch in the existing process,
not the newly created one. This appears to stretch back into even the
"history.git" tree. Luckily, dumpability is later set in commit_creds().
In earlier kernel versions before creds existed, similar checks also
existed late in the exec flow, covering up the mistake as far back as I
could find.
Note that because the commit_creds() check examines differences of euid,
uid, egid, gid, and capabilities between the old and new creds, it would
look like the setup_new_exec() dumpability test could be entirely removed.
However, the secureexec test may cover a different set of tests (specific
to the LSMs) than what commit_creds() checks for. So, fix this test to
use secureexec (the removed euid tests are redundant to the commoncap
secureexec checks now).
Cc: David Howells <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Acked-by: Serge Hallyn <[email protected]>
Reviewed-by: James Morris <[email protected]>
Is it time to think about reverting?
Thanks,
Laura
