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Mathias Krause b59eaa682e sched/fair: Prevent dead task groups from regaining cfs_rq's 
Kevin is reporting crashes which point to a use-after-free of a cfs_rq
in update_blocked_averages(). Initial debugging revealed that we've
live cfs_rq's (on_list=1) in an about to be kfree()'d task group in
free_fair_sched_group(). However, it was unclear how that can happen.

His kernel config happened to lead to a layout of struct sched_entity
that put the 'my_q' member directly into the middle of the object
which makes it incidentally overlap with SLUB's freelist pointer.
That, in combination with SLAB_FREELIST_HARDENED's freelist pointer
mangling, leads to a reliable access violation in form of a #GP which
made the UAF fail fast.

Michal seems to have run into the same issue[1]. He already correctly
diagnosed that commit a7b359fc6a37 ("sched/fair: Correctly insert
cfs_rq's to list on unthrottle") is causing the preconditions for the
UAF to happen by re-adding cfs_rq's also to task groups that have no
more running tasks, i.e. also to dead ones. His analysis, however,
misses the real root cause and it cannot be seen from the crash
backtrace only, as the real offender is tg_unthrottle_up() getting
called via sched_cfs_period_timer() via the timer interrupt at an
inconvenient time.

When unregister_fair_sched_group() unlinks all cfs_rq's from the dying
task group, it doesn't protect itself from getting interrupted. If the
timer interrupt triggers while we iterate over all CPUs or after
unregister_fair_sched_group() has finished but prior to unlinking the
task group, sched_cfs_period_timer() will execute and walk the list of
task groups, trying to unthrottle cfs_rq's, i.e. re-add them to the
dying task group. These will later -- in free_fair_sched_group() -- be
kfree()'ed while still being linked, leading to the fireworks Kevin
and Michal are seeing.

To fix this race, ensure the dying task group gets unlinked first.
However, simply switching the order of unregistering and unlinking the
task group isn't sufficient, as concurrent RCU walkers might still see
it, as can be seen below:

    CPU1:                                      CPU2:
      :                                        timer IRQ:
      :                                          do_sched_cfs_period_timer():
      :                                            :
      :                                            distribute_cfs_runtime():
      :                                              rcu_read_lock();
      :                                              :
      :                                              unthrottle_cfs_rq():
    sched_offline_group():                             :
      :                                                walk_tg_tree_from(…,tg_unthrottle_up,…):
      list_del_rcu(&tg->list);                           :
 (1)  :                                                  list_for_each_entry_rcu(child, &parent->children, siblings)
      :                                                    :
 (2)  list_del_rcu(&tg->siblings);                         :
      :                                                    tg_unthrottle_up():
      unregister_fair_sched_group():                         struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
        :                                                    :
        list_del_leaf_cfs_rq(tg->cfs_rq[cpu]);               :
        :                                                    :
        :                                                    if (!cfs_rq_is_decayed(cfs_rq) || cfs_rq->nr_running)
 (3)    :                                                        list_add_leaf_cfs_rq(cfs_rq);
      :                                                      :
      :                                                    :
      :                                                  :
      :                                                :
      :                                              :
 (4)  :                                              rcu_read_unlock();

CPU 2 walks the task group list in parallel to sched_offline_group(),
specifically, it'll read the soon to be unlinked task group entry at
(1). Unlinking it on CPU 1 at (2) therefore won't prevent CPU 2 from
still passing it on to tg_unthrottle_up(). CPU 1 now tries to unlink
all cfs_rq's via list_del_leaf_cfs_rq() in
unregister_fair_sched_group().  Meanwhile CPU 2 will re-add some of
these at (3), which is the cause of the UAF later on.

To prevent this additional race from happening, we need to wait until
walk_tg_tree_from() has finished traversing the task groups, i.e.
after the RCU read critical section ends in (4). Afterwards we're safe
to call unregister_fair_sched_group(), as each new walk won't see the
dying task group any more.

On top of that, we need to wait yet another RCU grace period after
unregister_fair_sched_group() to ensure print_cfs_stats(), which might
run concurrently, always sees valid objects, i.e. not already free'd
ones.

This patch survives Michal's reproducer[2] for 8h+ now, which used to
trigger within minutes before.

  [1] https://lore.kernel.org/lkml/20211011172236.11223-1-mkoutny@suse.com/
  [2] https://lore.kernel.org/lkml/20211102160228.GA57072@blackbody.suse.cz/

Fixes: a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on unthrottle")
[peterz: shuffle code around a bit]
Reported-by: Kevin Tanguy <kevin.tanguy@corp.ovh.com>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
2024-12-18 12:21:30 +01:00
.github/workflows
android
arch configs: drop HICCUP_CC_DISABLE 2024-12-18 12:15:20 +01:00
block block: fix ordering between checking BLK_MQ_S_STOPPED request adding 2024-12-17 13:24:19 +01:00
certs
crypto crypto: pcrypt - Call crypto layer directly when padata_do_parallel() return -EBUSY 2024-12-17 13:23:59 +01:00
Documentation PCI: Add 'reset_subordinate' to reset hierarchy below bridge 2024-12-17 13:24:32 +01:00
drivers battery: sm5451_charger: fix build on 5.10 2024-12-18 12:15:56 +01:00
firmware/tsp_goodix
fs jffs2: Fix rtime decompressor 2024-12-17 13:24:34 +01:00
gki
include sched/fair: Wait before decaying max_newidle_lb_cost 2024-12-18 12:21:16 +01:00
init initramfs: avoid filename buffer overrun 2024-12-17 13:23:59 +01:00
io_uring io_uring: fix possible deadlock in io_register_iowq_max_workers() 2024-11-30 02:33:28 +01:00
ipc Revert "Make more sysctl constants read-only" 2024-12-03 19:56:17 +01:00
kernel sched/fair: Prevent dead task groups from regaining cfs_rq's 2024-12-18 12:21:30 +01:00
kernel_build Reapply "configs: disable some unnecessary DSS stuff" 2024-12-18 11:24:28 +01:00
KernelSU@b766b98513 Added KernelSU 2024-11-19 23:08:59 +01:00
kunitconfigs
lib Revert "lib/Kconfig.debug: Remove DEBUG_KERNEL depend on DEBUG_KMEMLEAK|SCHED_DEBUG|SCHEDSTATS" 2024-12-18 11:09:39 +01:00
LICENSES
mm Reapply "mm: vmstat: use power efficient workingqueues" 2024-12-18 11:25:22 +01:00
net netpoll: Use rcu_access_pointer() in __netpoll_setup 2024-12-17 13:24:31 +01:00
samples samples/bpf: Fix a resource leak 2024-12-17 13:24:30 +01:00
scripts modpost: Add .irqentry.text to OTHER_SECTIONS 2024-12-17 13:24:34 +01:00
security apparmor: test: Fix memory leak for aa_unpack_strdup() 2024-12-17 13:24:18 +01:00
sound Revert "ALSA: usb-audio: Fix Yamaha P-125 Quirk Entry" 2024-12-17 14:46:18 +01:00
test
tools kselftest/arm64: Don't leak pipe fds in pac.exec_sign_all() 2024-12-17 13:24:29 +01:00
usr
virt Revert "KVM: Fix a data race on last_boosted_vcpu in kvm_vcpu_on_spin()" 2024-11-24 00:22:53 +01:00
build.config.aarch64
build.config.allmodconfig
build.config.allmodconfig.aarch64
build.config.allmodconfig.arm
build.config.allmodconfig.x86_64
build.config.amlogic
build.config.arm
build.config.common
build.config.db845c
build.config.erd8825_a25_s
build.config.erd8825_s
build.config.erd9925_evt0_s
build.config.erd9925_evt0_s5300_s
build.config.erd9925_s
build.config.gki
build.config.gki-debug.aarch64
build.config.gki-debug.x86_64
build.config.gki.aarch64
build.config.gki.aarch64.fips140
build.config.gki.aarch64.fips140_eval_testing
build.config.gki.x86_64
build.config.gki_kasan
build.config.gki_kasan.aarch64
build.config.gki_kasan.x86_64
build.config.gki_kprobes
build.config.gki_kprobes.aarch64
build.config.gki_kprobes.x86_64
build.config.hikey960
build.config.khwasan
build.config.mcd
build.config.rockchip
build.config.universal2100_s
build.config.universal8825_s
build.config.universal9925_evt0_s
build.config.universal9925_s
build.config.x86_64
build.sh build.sh: Fixup 2024-12-03 18:20:43 +01:00
COPYING
CREDITS
Kbuild
Kconfig
linux-stable.sh
MAINTAINERS
Makefile Revert "BACKPORT: FROMGIT: kbuild: Remove support for Clang's ThinLTO caching" 2024-12-18 11:08:09 +01:00
OWNERS
README
README.md
vendor_boot_module_order_exynos2100.cfg
vendor_boot_module_order_s5e8825.cfg
vendor_boot_module_order_s5e9925.cfg
vendor_module_list_s5e8825.cfg
vendor_module_list_s5e9925.cfg
vendor_module_list_s5e9925_b0s.cfg
vendor_module_list_s5e9925_g0s.cfg
vendor_module_list_s5e9925_r0s.cfg

README.md

How do I submit patches to Android Common Kernels

  1. BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.

    • Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux, additions of EXPORT_SYMBOL_GPL() require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.
    • When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.

  2. LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.

Common Kernel patch requirements

  • All patches must conform to the Linux kernel coding standards and pass script/checkpatch.pl
  • Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
  • If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch: UPSTREAM:, BACKPORT:, FROMGIT:, FROMLIST:, or ANDROID:.
  • All patches must have a Change-Id: tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
  • If an Android bug has been assigned, there must be a Bug: tag.
  • All patches must have a Signed-off-by: tag by the author and the submitter

Additional requirements are listed below based on patch type

Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:

  • If the patch is a cherry-pick from Linux mainline with no changes at all
    • tag the patch subject with UPSTREAM:.
    • add upstream commit information with a (cherry picked from commit ...) line
    • Example:
      • if the upstream commit message is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        UPSTREAM: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch requires any changes from the upstream version, tag the patch with BACKPORT: instead of UPSTREAM:.
    • use the same tags as UPSTREAM:
    • add comments about the changes under the (cherry picked from commit ...) line
    • Example:
        BACKPORT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        [joe: Resolved minor conflict in drivers/foo/bar.c ]
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for other backports: FROMGIT:, FROMLIST:,

  • If the patch has been merged into an upstream maintainer tree, but has not yet been merged into Linux mainline
    • tag the patch subject with FROMGIT:
    • add info on where the patch came from as (cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't use linux-next for example).
    • if changes were required, use BACKPORT: FROMGIT:
    • Example:
      • if the commit message in the maintainer tree is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        FROMGIT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
         https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch has been submitted to LKML, but not accepted into any maintainer tree
    • tag the patch subject with FROMLIST:
    • add a Link: tag with a link to the submittal on lore.kernel.org
    • add a Bug: tag with the Android bug (required for patches not accepted into a maintainer tree)
    • if changes were required, use BACKPORT: FROMLIST:
    • Example:
        FROMLIST: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for Android-specific patches: ANDROID:

  • If the patch is fixing a bug to Android-specific code
    • tag the patch subject with ANDROID:
    • add a Fixes: tag that cites the patch with the bug
    • Example:
        ANDROID: fix android-specific bug in foobar.c

        This is the detailed description of the important fix

        Fixes: 1234abcd2468 ("foobar: add cool feature")
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch is a new feature
    • tag the patch subject with ANDROID:
    • add a Bug: tag with the Android bug (required for android-specific features)