linux-stable.git/include/linux, branch v3.16.48

ptrace: use fsuid, fsgid, effective creds for fs access checks

2017-09-15T17:30:17+00:00

commit caaee6234d05a58c5b4d05e7bf766131b810a657 upstream.

By checking the effective credentials instead of the real UID / permitted
capabilities, ensure that the calling process actually intended to use its
credentials.

To ensure that all ptrace checks use the correct caller credentials (e.g.
in case out-of-tree code or newly added code omits the PTRACE_MODE_*CREDS
flag), use two new flags and require one of them to be set.

The problem was that when a privileged task had temporarily dropped its
privileges, e.g.  by calling setreuid(0, user_uid), with the intent to
perform following syscalls with the credentials of a user, it still passed
ptrace access checks that the user would not be able to pass.

While an attacker should not be able to convince the privileged task to
perform a ptrace() syscall, this is a problem because the ptrace access
check is reused for things in procfs.

In particular, the following somewhat interesting procfs entries only rely
on ptrace access checks:

 /proc/$pid/stat - uses the check for determining whether pointers
     should be visible, useful for bypassing ASLR
 /proc/$pid/maps - also useful for bypassing ASLR
 /proc/$pid/cwd - useful for gaining access to restricted
     directories that contain files with lax permissions, e.g. in
     this scenario:
     lrwxrwxrwx root root /proc/13020/cwd -> /root/foobar
     drwx------ root root /root
     drwxr-xr-x root root /root/foobar
     -rw-r--r-- root root /root/foobar/secret

Therefore, on a system where a root-owned mode 6755 binary changes its
effective credentials as described and then dumps a user-specified file,
this could be used by an attacker to reveal the memory layout of root's
processes or reveal the contents of files he is not allowed to access
(through /proc/$pid/cwd).

[akpm@linux-foundation.org: fix warning]
Signed-off-by: Jann Horn 
Acked-by: Kees Cook 
Cc: Casey Schaufler 
Cc: Oleg Nesterov 
Cc: Ingo Molnar 
Cc: James Morris 
Cc: "Serge E. Hallyn" 
Cc: Andy Shevchenko 
Cc: Andy Lutomirski 
Cc: Al Viro 
Cc: "Eric W. Biederman" 
Cc: Willy Tarreau 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.16:
 - Update mm_access() calls in fs/proc/task_{,no}mmu.c too
 - Adjust context]
Signed-off-by: Ben Hutchings

srcu: Allow use of Classic SRCU from both process and interrupt context

2017-09-15T17:30:07+00:00

commit 1123a6041654e8f889014659593bad4168e542c2 upstream.

Linu Cherian reported a WARN in cleanup_srcu_struct() when shutting
down a guest running iperf on a VFIO assigned device.  This happens
because irqfd_wakeup() calls srcu_read_lock(&kvm->irq_srcu) in interrupt
context, while a worker thread does the same inside kvm_set_irq().  If the
interrupt happens while the worker thread is executing __srcu_read_lock(),
updates to the Classic SRCU ->lock_count[] field or the Tree SRCU
->srcu_lock_count[] field can be lost.

The docs say you are not supposed to call srcu_read_lock() and
srcu_read_unlock() from irq context, but KVM interrupt injection happens
from (host) interrupt context and it would be nice if SRCU supported the
use case.  KVM is using SRCU here not really for the "sleepable" part,
but rather due to its IPI-free fast detection of grace periods.  It is
therefore not desirable to switch back to RCU, which would effectively
revert commit 719d93cd5f5c ("kvm/irqchip: Speed up KVM_SET_GSI_ROUTING",
2014-01-16).

However, the docs are overly conservative.  You can have an SRCU instance
only has users in irq context, and you can mix process and irq context
as long as process context users disable interrupts.  In addition,
__srcu_read_unlock() actually uses this_cpu_dec() on both Tree SRCU and
Classic SRCU.  For those two implementations, only srcu_read_lock()
is unsafe.

When Classic SRCU's __srcu_read_unlock() was changed to use this_cpu_dec(),
in commit 5a41344a3d83 ("srcu: Simplify __srcu_read_unlock() via
this_cpu_dec()", 2012-11-29), __srcu_read_lock() did two increments.
Therefore it kept __this_cpu_inc(), with preempt_disable/enable in
the caller.  Tree SRCU however only does one increment, so on most
architectures it is more efficient for __srcu_read_lock() to use
this_cpu_inc(), and any performance differences appear to be down in
the noise.

Fixes: 719d93cd5f5c ("kvm/irqchip: Speed up KVM_SET_GSI_ROUTING")
Reported-by: Linu Cherian 
Suggested-by: Linu Cherian 
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini 
Cc: Linus Torvalds 
Signed-off-by: Paul E. McKenney 
[bwh: Backported to 3.16: __srcu_read_lock() still updates two different
 counters.  So follow what  _this_cpu_generic_to_op() does and use
 raw_local_irq_{save,restore}() and raw_cpu_ptr().]
Signed-off-by: Ben Hutchings

rcu: Move preemption disabling out of __srcu_read_lock()

2017-09-15T17:30:07+00:00

commit 49f5903b473c5f63f3b57856d1bd4593db0a2eef upstream.

Currently, __srcu_read_lock() cannot be invoked from restricted
environments because it contains calls to preempt_disable() and
preempt_enable(), both of which can invoke lockdep, which is a bad
idea in some restricted execution modes.  This commit therefore moves
the preempt_disable() and preempt_enable() from __srcu_read_lock()
to srcu_read_lock().  It also inserts the preempt_disable() and
preempt_enable() around the call to __srcu_read_lock() in do_exit().

Signed-off-by: Paul E. McKenney 
Reviewed-by: Josh Triplett 
[bwh: Backported to 3.16:
 - Drop changes in do_exit()
 - Adjust context]
Signed-off-by: Ben Hutchings

tracing/kprobes: Enforce kprobes teardown after testing

2017-09-15T17:29:43+00:00

commit 30e7d894c1478c88d50ce94ddcdbd7f9763d9cdd upstream.

Enabling the tracer selftest triggers occasionally the warning in
text_poke(), which warns when the to be modified page is not marked
reserved.

The reason is that the tracer selftest installs kprobes on functions marked
__init for testing. These probes are removed after the tests, but that
removal schedules the delayed kprobes_optimizer work, which will do the
actual text poke. If the work is executed after the init text is freed,
then the warning triggers. The bug can be reproduced reliably when the work
delay is increased.

Flush the optimizer work and wait for the optimizing/unoptimizing lists to
become empty before returning from the kprobes tracer selftest. That
ensures that all operations which were queued due to the probes removal
have completed.

Link: http://lkml.kernel.org/r/20170516094802.76a468bb@gandalf.local.home

Signed-off-by: Thomas Gleixner 
Acked-by: Masami Hiramatsu 
Fixes: 6274de498 ("kprobes: Support delayed unoptimizing")
Signed-off-by: Steven Rostedt (VMware) 
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings

net/mlx4: Fix the check in attaching steering rules

2017-08-26T01:14:50+00:00

commit 6dc06c08bef1c746ff8da33dab677cfbacdcad32 upstream.

Our previous patch (cited below) introduced a regression
for RAW Eth QPs.

Fix it by checking if the QP number provided by user-space
exists, hence allowing steering rules to be added for valid
QPs only.

Fixes: 89c557687a32 ("net/mlx4_en: Avoid adding steering rules with invalid ring")
Reported-by: Or Gerlitz 
Signed-off-by: Talat Batheesh 
Signed-off-by: Tariq Toukan 
Acked-by: Or Gerlitz 
Reviewed-by: Leon Romanovsky 
Signed-off-by: David S. Miller 
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings

dentry name snapshots

2017-08-26T01:14:48+00:00

commit 49d31c2f389acfe83417083e1208422b4091cd9e upstream.

take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified).  In either case the pointer to stable
string is stored into the same structure.

dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().

Intended use:
	struct name_snapshot s;

	take_dentry_name_snapshot(&s, dentry);
	...
	access s.name
	...
	release_dentry_name_snapshot(&s);

Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.

Signed-off-by: Al Viro 
[carnil: backport 4.9: adjust context]
[bwh: Backported to 3.16:
 - External names are not ref-counted, so copy them
 - Adjust context]
Signed-off-by: Ben Hutchings

ima: pass 'opened' flag to identify newly created files

2017-08-26T01:14:23+00:00

commit 3034a146820c26fe6da66a45f6340fe87fe0983a upstream.

Empty files and missing xattrs do not guarantee that a file was
just created.  This patch passes FILE_CREATED flag to IMA to
reliably identify new files.

Signed-off-by: Dmitry Kasatkin 
Signed-off-by: Mimi Zohar 
[bwh: Backported to 3.16: drop change to ima_fw_from_file()]
Signed-off-by: Ben Hutchings

include/linux/kernel.h: change abs() macro so it uses consistent return type

2017-07-18T17:40:28+00:00

commit 8f57e4d930d48217268315898212518d4d3e0773 upstream.

Rewrite abs() so that its return type does not depend on the
architecture and no unexpected type conversion happen inside of it.  The
only conversion is from unsigned to signed type.  char is left as a
return type but treated as a signed type regradless of it's actual
signedness.

With the old version, int arguments were promoted to long and depending
on architecture a long argument might result in s64 or long return type
(which may or may not be the same).

This came after some back and forth with Nicolas.  The current macro has
different return type (for the same input type) depending on
architecture which might be midly iritating.

An alternative version would promote to int like so:

	#define abs(x)	__abs_choose_expr(x, long long,			\
			__abs_choose_expr(x, long,			\
			__builtin_choose_expr(				\
				sizeof(x) <= sizeof(int),		\
				({ int __x = (x); __x<0?-__x:__x; }),	\
				((void)0))))

I have no preference but imagine Linus might.  :] Nicolas argument against
is that promoting to int causes iconsistent behaviour:

	int main(void) {
		unsigned short a = 0, b = 1, c = a - b;
		unsigned short d = abs(a - b);
		unsigned short e = abs(c);
		printf("%u %u\n", d, e);  // prints: 1 65535
	}

Then again, no sane person expects consistent behaviour from C integer
arithmetic.  ;)

Note:

  __builtin_types_compatible_p(unsigned char, char) is always false, and
  __builtin_types_compatible_p(signed char, char) is also always false.

Signed-off-by: Michal Nazarewicz 
Reviewed-by: Nicolas Pitre 
Cc: Srinivas Pandruvada 
Cc: Wey-Yi Guy 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings

kernel.h: make abs() work with 64-bit types

2017-07-18T17:40:28+00:00

commit c8299cb605b27dd5a49f7a69e48fd23e5a206298 upstream.

For 64-bit arguments, the abs macro casts it to an int which leads to
lost precision and may cause incorrect results.  To deal with 64-bit
types abs64 macro has been introduced but still there are places where
abs macro is used incorrectly.

To deal with the problem, expand abs macro such that it operates on s64
type when dealing with 64-bit types while still returning long when
dealing with smaller types.

This fixes one known bug (per John):

The internal clocksteering done for fine-grained error correction uses a
: logarithmic approximation, so any time adjtimex() adjusts the clock
: steering, timekeeping_freqadjust() quickly approximates the correct clock
: frequency over a series of ticks.
:
: Unfortunately, the logic in timekeeping_freqadjust(), introduced in commit
: dc491596f639438 (Rework frequency adjustments to work better w/ nohz),
: used the abs() function with a s64 error value to calculate the size of
: the approximated adjustment to be made.
:
: Per include/linux/kernel.h: "abs() should not be used for 64-bit types
: (s64, u64, long long) - use abs64()".
:
: Thus on 32-bit platforms, this resulted in the clocksteering to take a
: quite dampended random walk trying to converge on the proper frequency,
: which caused the adjustments to be made much slower then intended (most
: easily observed when large adjustments are made).

Signed-off-by: Michal Nazarewicz 
Reported-by: John Stultz 
Tested-by: John Stultz 
Cc: Ingo Molnar 
Cc: Steven Rostedt 
Cc: Peter Zijlstra 
Cc: Masami Hiramatsu 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Ben Hutchings

KVM: kvm_io_bus_unregister_dev() should never fail

2017-07-18T17:40:22+00:00

commit 90db10434b163e46da413d34db8d0e77404cc645 upstream.

No caller currently checks the return value of
kvm_io_bus_unregister_dev(). This is evil, as all callers silently go on
freeing their device. A stale reference will remain in the io_bus,
getting at least used again, when the iobus gets teared down on
kvm_destroy_vm() - leading to use after free errors.

There is nothing the callers could do, except retrying over and over
again.

So let's simply remove the bus altogether, print an error and make
sure no one can access this broken bus again (returning -ENOMEM on any
attempt to access it).

Fixes: e93f8a0f821e ("KVM: convert io_bus to SRCU")
Reported-by: Dmitry Vyukov 
Reviewed-by: Cornelia Huck 
Signed-off-by: David Hildenbrand 
Signed-off-by: Paolo Bonzini 
[bwh: Backported to 3.16:
 - Drop changes to kvm_io_bus_get_dev()
 - Adjust context]
Signed-off-by: Ben Hutchings