linux-toradex.git/fs/exec.c, branch v3.2.73

fs: take i_mutex during prepare_binprm for set[ug]id executables

2015-05-09T22:16:36+00:00

commit 8b01fc86b9f425899f8a3a8fc1c47d73c2c20543 upstream.

This prevents a race between chown() and execve(), where chowning a
setuid-user binary to root would momentarily make the binary setuid
root.

This patch was mostly written by Linus Torvalds.

Signed-off-by: Jann Horn 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.2:
 - Drop the task_no_new_privs() and user namespace checks
 - Open-code file_inode()
 - s/READ_ONCE/ACCESS_ONCE/
 - Adjust context]
Signed-off-by: Ben Hutchings

exec/ptrace: fix get_dumpable() incorrect tests

2014-01-03T04:33:21+00:00

commit d049f74f2dbe71354d43d393ac3a188947811348 upstream.

The get_dumpable() return value is not boolean.  Most users of the
function actually want to be testing for non-SUID_DUMP_USER(1) rather than
SUID_DUMP_DISABLE(0).  The SUID_DUMP_ROOT(2) is also considered a
protected state.  Almost all places did this correctly, excepting the two
places fixed in this patch.

Wrong logic:
    if (dumpable == SUID_DUMP_DISABLE) { /* be protective */ }
        or
    if (dumpable == 0) { /* be protective */ }
        or
    if (!dumpable) { /* be protective */ }

Correct logic:
    if (dumpable != SUID_DUMP_USER) { /* be protective */ }
        or
    if (dumpable != 1) { /* be protective */ }

Without this patch, if the system had set the sysctl fs/suid_dumpable=2, a
user was able to ptrace attach to processes that had dropped privileges to
that user.  (This may have been partially mitigated if Yama was enabled.)

The macros have been moved into the file that declares get/set_dumpable(),
which means things like the ia64 code can see them too.

CVE-2013-2929

Reported-by: Vasily Kulikov 
Signed-off-by: Kees Cook 
Cc: "Luck, Tony" 
Cc: Oleg Nesterov 
Cc: "Eric W. Biederman" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings

perf: Disable monitoring on setuid processes for regular users

2013-07-27T04:34:19+00:00

commit 2976b10f05bd7f6dab9f9e7524451ddfed656a89 upstream.

There was a a bug in setup_new_exec(), whereby
the test to disabled perf monitoring was not
correct because the new credentials for the
process were not yet committed and therefore
the get_dumpable() test was never firing.

The patch fixes the problem by moving the
perf_event test until after the credentials
are committed.

Signed-off-by: Stephane Eranian 
Tested-by: Jiri Olsa 
Acked-by: Peter Zijlstra 
Signed-off-by: Ingo Molnar 
Signed-off-by: Ben Hutchings

exec: use -ELOOP for max recursion depth

2013-03-06T03:24:28+00:00

commit d740269867021faf4ce38a449353d2b986c34a67 upstream.

To avoid an explosion of request_module calls on a chain of abusive
scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
as maximum recursion depth is hit, the error will fail all the way back
up the chain, aborting immediately.

This also has the side-effect of stopping the user's shell from attempting
to reexecute the top-level file as a shell script. As seen in the
dash source:

        if (cmd != path_bshell && errno == ENOEXEC) {
                *argv-- = cmd;
                *argv = cmd = path_bshell;
                goto repeat;
        }

The above logic was designed for running scripts automatically that lacked
the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
things continue to behave as the shell expects.

Additionally, when tracking recursion, the binfmt handlers should not be
involved. The recursion being tracked is the depth of calls through
search_binary_handler(), so that function should be exclusively responsible
for tracking the depth.

Signed-off-by: Kees Cook 
Cc: halfdog 
Cc: P J P 
Cc: Alexander Viro 
Signed-off-by: Andrew Morton 
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings

exec: do not leave bprm->interp on stack

2013-01-03T03:33:45+00:00

commit b66c5984017533316fd1951770302649baf1aa33 upstream.

If a series of scripts are executed, each triggering module loading via
unprintable bytes in the script header, kernel stack contents can leak
into the command line.

Normally execution of binfmt_script and binfmt_misc happens recursively.
However, when modules are enabled, and unprintable bytes exist in the
bprm->buf, execution will restart after attempting to load matching
binfmt modules.  Unfortunately, the logic in binfmt_script and
binfmt_misc does not expect to get restarted.  They leave bprm->interp
pointing to their local stack.  This means on restart bprm->interp is
left pointing into unused stack memory which can then be copied into the
userspace argv areas.

After additional study, it seems that both recursion and restart remains
the desirable way to handle exec with scripts, misc, and modules.  As
such, we need to protect the changes to interp.

This changes the logic to require allocation for any changes to the
bprm->interp.  To avoid adding a new kmalloc to every exec, the default
value is left as-is.  Only when passing through binfmt_script or
binfmt_misc does an allocation take place.

For a proof of concept, see DoTest.sh from:

   http://www.halfdog.net/Security/2012/LinuxKernelBinfmtScriptStackDataDisclosure/

Signed-off-by: Kees Cook 
Cc: halfdog 
Cc: P J P 
Cc: Alexander Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

freezer: PF_FREEZER_NOSIG should be cleared along with PF_NOFREEZE

2013-01-03T03:32:42+00:00

This patch is only for pre-v3.3 stable trees which backported
b40a7959 "freezer: exec should clear PF_NOFREEZE along with PF_KTHREAD".
v3.3+ doesn't need this fix.

b40a7959 is the trivial bugfix, but unfortunately I forgot that
until 34b087e4 "freezer: kill unused set_freezable_with_signal()"
there were another only-for-kernel-threads flag, PF_FREEZER_NOSIG,
which should be cleared as well.

See https://bugs.launchpad.net/ubuntu/+source/v86d/+bug/1080530
The freezer fails because it expects that a PF_FREEZER_NOSIG task
doesn't need a signal. Before b40a7959 it wrongly succeeds leaving
the PF_NOFREEZE | PF_FREEZER_NOSIG task unfrozen.

Reported-and-tested-by: Joseph Salisbury 
Signed-off-by: Oleg Nesterov 
[bwh: Don't touch PF_FORKNOEXEC; it's cleared elsewhere]
Signed-off-by: Ben Hutchings

freezer: exec should clear PF_NOFREEZE along with PF_KTHREAD

2012-10-30T23:27:06+00:00

commit b40a79591ca918e7b91b0d9b6abd5d00f2e88c19 upstream.

flush_old_exec() clears PF_KTHREAD but forgets about PF_NOFREEZE.

Signed-off-by: Oleg Nesterov 
Acked-by: Tejun Heo 
Signed-off-by: Rafael J. Wysocki 
[bwh: Backported to 3.2: PF_FORKNOEXEC is cleared elsewhere]
Signed-off-by: Ben Hutchings

exit_signal: simplify the "we have changed execution domain" logic

2012-05-11T12:15:03+00:00

commit e636825346b36a07ccfc8e30946d52855e21f681 upstream.

exit_notify() checks "tsk->self_exec_id != tsk->parent_exec_id"
to handle the "we have changed execution domain" case.

We can change do_thread() to always set ->exit_signal = SIGCHLD
and remove this check to simplify the code.

We could change setup_new_exec() instead, this looks more logical
because it increments ->self_exec_id. But note that de_thread()
already resets ->exit_signal if it changes the leader, let's keep
both changes close to each other.

Note that we change ->exit_signal lockless, this changes the rules.
Thereafter ->exit_signal is not stable under tasklist but this is
fine, the only possible change is OLDSIG -> SIGCHLD. This can race
with eligible_child() but the race is harmless. We can race with
reparent_leader() which changes our ->exit_signal in parallel, but
it does the same change to SIGCHLD.

The noticeable user-visible change is that the execing task is not
"visible" to do_wait()->eligible_child(__WCLONE) right after exec.
To me this looks more logical, and this is consistent with mt case.

Signed-off-by: Oleg Nesterov 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

oom: remove oom_disable_count

2011-11-01T00:30:45+00:00

This removes mm->oom_disable_count entirely since it's unnecessary and
currently buggy.  The counter was intended to be per-process but it's
currently decremented in the exit path for each thread that exits, causing
it to underflow.

The count was originally intended to prevent oom killing threads that
share memory with threads that cannot be killed since it doesn't lead to
future memory freeing.  The counter could be fixed to represent all
threads sharing the same mm, but it's better to remove the count since:

 - it is possible that the OOM_DISABLE thread sharing memory with the
   victim is waiting on that thread to exit and will actually cause
   future memory freeing, and

 - there is no guarantee that a thread is disabled from oom killing just
   because another thread sharing its mm is oom disabled.

Signed-off-by: David Rientjes 
Reported-by: Oleg Nesterov 
Reviewed-by: Oleg Nesterov 
Cc: Ying Han 
Cc: KOSAKI Motohiro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

move RLIMIT_NPROC check from set_user() to do_execve_common()

2011-08-11T18:24:42+00:00

The patch http://lkml.org/lkml/2003/7/13/226 introduced an RLIMIT_NPROC
check in set_user() to check for NPROC exceeding via setuid() and
similar functions.

Before the check there was a possibility to greatly exceed the allowed
number of processes by an unprivileged user if the program relied on
rlimit only.  But the check created new security threat: many poorly
written programs simply don't check setuid() return code and believe it
cannot fail if executed with root privileges.  So, the check is removed
in this patch because of too often privilege escalations related to
buggy programs.

The NPROC can still be enforced in the common code flow of daemons
spawning user processes.  Most of daemons do fork()+setuid()+execve().
The check introduced in execve() (1) enforces the same limit as in
setuid() and (2) doesn't create similar security issues.

Neil Brown suggested to track what specific process has exceeded the
limit by setting PF_NPROC_EXCEEDED process flag.  With the change only
this process would fail on execve(), and other processes' execve()
behaviour is not changed.

Solar Designer suggested to re-check whether NPROC limit is still
exceeded at the moment of execve().  If the process was sleeping for
days between set*uid() and execve(), and the NPROC counter step down
under the limit, the defered execve() failure because NPROC limit was
exceeded days ago would be unexpected.  If the limit is not exceeded
anymore, we clear the flag on successful calls to execve() and fork().

The flag is also cleared on successful calls to set_user() as the limit
was exceeded for the previous user, not the current one.

Similar check was introduced in -ow patches (without the process flag).

v3 - clear PF_NPROC_EXCEEDED on successful calls to set_user().

Reviewed-by: James Morris 
Signed-off-by: Vasiliy Kulikov 
Acked-by: NeilBrown 
Signed-off-by: Linus Torvalds