On Mon, Sep 27, 2021 at 09:37:58AM -0700, Luis Chamberlain wrote: > This extends test_sysfs with support for using the failure injection > wait completion and knobs to force a few race conditions which > demonstrates that kernfs active reference protection is sufficient > for kobject / device protection at higher layers. > > This adds 4 new tests which tries to remove the device attribute > store operation in 4 different situations: > > 1) at the start of kernfs_kernfs_fop_write_iter() > 2) before the of->mutex is held in kernfs_kernfs_fop_write_iter() > 3) after the of->mutex is held in kernfs_kernfs_fop_write_iter() > 4) after the kernfs node active reference is taken > > A write fails in call cases except the last one, test number #32. There > is a good explanation for this: *once* kernfs_get_active() gets called > we have a guarantee that the kernfs entry cannot be removed. If > kernfs_get_active() succeeds that entry cannot be removed and so > anything trying to remove that entry will have to wait. It is perhaps > not obvious but since a sysfs write will trigger eventually a > kernfs_get_active() call, and *only* if this succeeds will the sysfs > op be called, this and the fact that you cannot remove the kernfs > entry while the kenfs entry is active implies that a module that > created the respective sysfs / kernfs entry *cannot* possibly be > removed during a sysfs operation. And test number 32 provides us with > proof of this. If it were not true test #32 should crash. > > No null dereferences are reproduced, even though this has been observed > in some complex testing cases [0]. If this issue really exists we should > have enough tools on the sysfs_test toolbox now to try to reproduce > this easily without having to poke around other drivers. It very likley > was the case that the issue reported [0] was possibly a side issue after > the first bug which was zram specific. This is why it is important to > isolate the issue and try to reproduce it in a generic form using the > test_sysfs driver. > > [0] https://lkml.kernel.org/r/20210623215007.862787-1-mcgrof@xxxxxxxxxx > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > --- > lib/Kconfig.debug | 3 + > lib/test_sysfs.c | 31 +++++ > tools/testing/selftests/sysfs/config | 3 + > tools/testing/selftests/sysfs/sysfs.sh | 175 +++++++++++++++++++++++++ > 4 files changed, 212 insertions(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index a29b7d398c4e..176b822654e5 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -2358,6 +2358,9 @@ config TEST_SYSFS > depends on SYSFS > depends on NET > depends on BLOCK > + select FAULT_INJECTION > + select FAULT_INJECTION_DEBUG_FS > + select FAIL_KERNFS_KNOBS I don't like seeing "select" for user-configurable CONFIGs -- things tend to end up weird. This should simply be: depends on FAIL_KERNFS_KNOBS > help > This builds the "test_sysfs" module. This driver enables to test the > sysfs file system safely without affecting production knobs which > diff --git a/lib/test_sysfs.c b/lib/test_sysfs.c > index 2043ca494af8..c6e62de61403 100644 > --- a/lib/test_sysfs.c > +++ b/lib/test_sysfs.c > @@ -38,6 +38,11 @@ > #include <linux/rtnetlink.h> > #include <linux/genhd.h> > #include <linux/blkdev.h> > +#include <linux/kernfs.h> > + > +#ifdef CONFIG_FAIL_KERNFS_KNOBS This isn't an optional config here (and following)? > +MODULE_IMPORT_NS(KERNFS_DEBUG_PRIVATE); > +#endif > > static bool enable_lock; > module_param(enable_lock, bool_enable_only, 0644); > @@ -82,6 +87,13 @@ static bool enable_verbose_rmmod; > module_param(enable_verbose_rmmod, bool_enable_only, 0644); > MODULE_PARM_DESC(enable_verbose_rmmod, "enable verbose print messages on rmmod"); > > +#ifdef CONFIG_FAIL_KERNFS_KNOBS > +static bool enable_completion_on_rmmod; > +module_param(enable_completion_on_rmmod, bool_enable_only, 0644); > +MODULE_PARM_DESC(enable_completion_on_rmmod, > + "enable sending a kernfs completion on rmmod"); > +#endif > + > static int sysfs_test_major; > > /** > @@ -285,6 +297,12 @@ static ssize_t config_show(struct device *dev, > "enable_verbose_writes:\t%s\n", > enable_verbose_writes ? "true" : "false"); > > +#ifdef CONFIG_FAIL_KERNFS_KNOBS > + len += snprintf(buf+len, PAGE_SIZE - len, > + "enable_completion_on_rmmod:\t%s\n", > + enable_completion_on_rmmod ? "true" : "false"); > +#endif > + > test_dev_config_unlock(test_dev); > > return len; > @@ -904,10 +922,23 @@ static int __init test_sysfs_init(void) > } > module_init(test_sysfs_init); > > +#ifdef CONFIG_FAIL_KERNFS_KNOBS > +/* The goal is to race our device removal with a pending kernfs -> store call */ > +static void test_sysfs_kernfs_send_completion_rmmod(void) > +{ > + if (!enable_completion_on_rmmod) > + return; > + complete(&kernfs_debug_wait_completion); > +} > +#else > +static inline void test_sysfs_kernfs_send_completion_rmmod(void) {} > +#endif > + > static void __exit test_sysfs_exit(void) > { > if (enable_debugfs) > debugfs_remove(debugfs_dir); > + test_sysfs_kernfs_send_completion_rmmod(); > if (delay_rmmod_ms) > msleep(delay_rmmod_ms); > unregister_test_dev_sysfs(first_test_dev); > diff --git a/tools/testing/selftests/sysfs/config b/tools/testing/selftests/sysfs/config > index 9196f452ecd5..2876a229f95b 100644 > --- a/tools/testing/selftests/sysfs/config > +++ b/tools/testing/selftests/sysfs/config > @@ -1,2 +1,5 @@ > CONFIG_SYSFS=m > CONFIG_TEST_SYSFS=m > +CONFIG_FAULT_INJECTION=y > +CONFIG_FAULT_INJECTION_DEBUG_FS=y > +CONFIG_FAIL_KERNFS_KNOBS=y > diff --git a/tools/testing/selftests/sysfs/sysfs.sh b/tools/testing/selftests/sysfs/sysfs.sh > index b3f4c2236c7f..f928635d0e35 100755 > --- a/tools/testing/selftests/sysfs/sysfs.sh > +++ b/tools/testing/selftests/sysfs/sysfs.sh > @@ -62,6 +62,10 @@ ALL_TESTS="$ALL_TESTS 0025:1:1:test_dev_y:block" > ALL_TESTS="$ALL_TESTS 0026:1:1:test_dev_y:block" > ALL_TESTS="$ALL_TESTS 0027:1:0:test_dev_x:block" # deadlock test > ALL_TESTS="$ALL_TESTS 0028:1:0:test_dev_x:block" # deadlock test with rntl_lock > +ALL_TESTS="$ALL_TESTS 0029:1:1:test_dev_x:block" # kernfs race removal of store > +ALL_TESTS="$ALL_TESTS 0030:1:1:test_dev_x:block" # kernfs race removal before mutex > +ALL_TESTS="$ALL_TESTS 0031:1:1:test_dev_x:block" # kernfs race removal after mutex > +ALL_TESTS="$ALL_TESTS 0032:1:1:test_dev_x:block" # kernfs race removal after active > > allow_user_defaults() > { > @@ -92,6 +96,9 @@ allow_user_defaults() > if [ -z $SYSFS_DEBUGFS_DIR ]; then > SYSFS_DEBUGFS_DIR="/sys/kernel/debug/test_sysfs" > fi > + if [ -z $KERNFS_DEBUGFS_DIR ]; then > + KERNFS_DEBUGFS_DIR="/sys/kernel/debug/kernfs" > + fi > if [ -z $PAGE_SIZE ]; then > PAGE_SIZE=$(getconf PAGESIZE) > fi > @@ -167,6 +174,14 @@ modprobe_reset_enable_rtnl_lock_on_rmmod() > unset FIRST_MODPROBE_ARGS > } > > +modprobe_reset_enable_completion() > +{ > + FIRST_MODPROBE_ARGS="enable_completion_on_rmmod=1 enable_verbose_writes=1" > + FIRST_MODPROBE_ARGS="$FIRST_MODPROBE_ARGS enable_verbose_rmmod=1 delay_rmmod_ms=0" > + modprobe_reset > + unset FIRST_MODPROBE_ARGS > +} > + > load_req_mod() > { > modprobe_reset > @@ -197,6 +212,63 @@ debugfs_reset_first_test_dev_ignore_errors() > echo -n "1" >"$SYSFS_DEBUGFS_DIR"/reset_first_test_dev > } > > +debugfs_kernfs_kernfs_fop_write_iter_exists() > +{ > + KNOB_DIR="${KERNFS_DEBUGFS_DIR}/config_fail_kernfs_fop_write_iter" > + if [[ ! -d $KNOB_DIR ]]; then > + echo "kernfs debugfs does not exist $KNOB_DIR" > + return 0; > + fi > + KNOB_DEBUGFS="${KERNFS_DEBUGFS_DIR}/fail_kernfs_fop_write_iter" > + if [[ ! -d $KNOB_DEBUGFS ]]; then > + echo -n "kernfs debugfs for coniguring fail_kernfs_fop_write_iter " > + echo "does not exist $KNOB_DIR" > + return 0; > + fi > + return 1 > +} > + > +debugfs_kernfs_kernfs_fop_write_iter_set_fail_once() > +{ > + KNOB_DEBUGFS="${KERNFS_DEBUGFS_DIR}/fail_kernfs_fop_write_iter" > + echo 1 > $KNOB_DEBUGFS/interval > + echo 100 > $KNOB_DEBUGFS/probability > + echo 0 > $KNOB_DEBUGFS/space > + # Disable verbose messages on the kernel ring buffer which may > + # confuse developers with a kernel panic. > + echo 0 > $KNOB_DEBUGFS/verbose > + > + # Fail only once > + echo 1 > $KNOB_DEBUGFS/times > +} > + > +debugfs_kernfs_kernfs_fop_write_iter_set_fail_never() > +{ > + KNOB_DEBUGFS="${KERNFS_DEBUGFS_DIR}/fail_kernfs_fop_write_iter" > + echo 0 > $KNOB_DEBUGFS/times > +} > + > +debugfs_kernfs_set_wait_ms() > +{ > + SLEEP_AFTER_WAIT_MS="${KERNFS_DEBUGFS_DIR}/sleep_after_wait_ms" > + echo $1 > $SLEEP_AFTER_WAIT_MS > +} > + > +debugfs_kernfs_disable_wait_kernfs_fop_write_iter() > +{ > + ENABLE_WAIT_KNOB="${KERNFS_DEBUGFS_DIR}/config_fail_kernfs_fop_write_iter/wait_" > + for KNOB in ${ENABLE_WAIT_KNOB}*; do > + echo 0 > $KNOB > + done > +} > + > +debugfs_kernfs_enable_wait_kernfs_fop_write_iter() > +{ > + ENABLE_WAIT_KNOB="${KERNFS_DEBUGFS_DIR}/config_fail_kernfs_fop_write_iter/wait_$1" > + echo -n "1" > $ENABLE_WAIT_KNOB > + return $? > +} > + > set_orig() > { > if [[ ! -z $TARGET ]] && [[ ! -z $ORIG ]]; then > @@ -972,6 +1044,105 @@ sysfs_test_0028() > fi > } > > +sysfs_race_kernfs_kernfs_fop_write_iter() > +{ > + TARGET="${DIR}/$(get_test_target $1)" > + WAIT_AT=$2 > + EXPECT_WRITE_RETURNS=$3 > + MSDELAY=$4 > + > + modprobe_reset_enable_completion > + ORIG=$(cat "${TARGET}") > + TEST_STR=$(( $ORIG + 1 )) > + > + echo -n "Test racing removal of sysfs store op with kernfs $WAIT_AT ... " > + > + if debugfs_kernfs_kernfs_fop_write_iter_exists; then > + echo -n "skipping test as CONFIG_FAIL_KERNFS_KNOBS " > + echo " or CONFIG_FAULT_INJECTION_DEBUG_FS is disabled" > + return $ksft_skip > + fi > + > + # Allow for failing the kernfs_kernfs_fop_write_iter call once, > + # we'll provide exact context shortly afterwards. > + debugfs_kernfs_kernfs_fop_write_iter_set_fail_once > + > + # First disable all waits > + debugfs_kernfs_disable_wait_kernfs_fop_write_iter > + > + # Enable a wait_for_completion(&kernfs_debug_wait_completion) at the > + # specified location inside the kernfs_fop_write_iter() routine > + debugfs_kernfs_enable_wait_kernfs_fop_write_iter $WAIT_AT > + > + # Configure kernfs so that after its wait_for_completion() it > + # will msleep() this amount of time and schedule(). We figure this > + # will be sufficient time to allow for our module removal to complete. > + debugfs_kernfs_set_wait_ms $MSDELAY > + > + # Now we trigger a kernfs write op, which will run kernfs_fop_write_iter, > + # but will wait until our driver sends a respective completion > + set_test_ignore_errors & > + write_pid=$! > + > + # At this point kernfs_fop_write_iter() hasn't run our op, its > + # waiting for our completion at the specified time $WAIT_AT. > + # We now remove our module which will send a > + # complete(&kernfs_debug_wait_completion) right before we deregister > + # our device and the sysfs device attributes are removed. > + # > + # After the completion is sent, the test_sysfs driver races with > + # kernfs to do the device deregistration with the kernfs msleep > + # and schedule(). This should mean we've forced trying to remove the > + # module prior to allowing kernfs to run our store operation. If the > + # race did happen we'll panic with a null dereference on the store op. > + # > + # If no race happens we should see no write operation triggered. > + modprobe -r $TEST_DRIVER > /dev/null 2>&1 > + > + debugfs_kernfs_kernfs_fop_write_iter_set_fail_never > + > + wait $write_pid > + if [[ $? -eq $EXPECT_WRITE_RETURNS ]]; then > + echo "ok" > + else > + echo "FAIL" >&2 > + fi > +} > + > +sysfs_test_0029() > +{ > + for delay in 0 2 4 8 16 32 64 128 246 512 1024; do > + echo "Using delay-after-completion: $delay" > + sysfs_race_kernfs_kernfs_fop_write_iter 0029 at_start 1 $delay > + done > +} > + > +sysfs_test_0030() > +{ > + for delay in 0 2 4 8 16 32 64 128 246 512 1024; do > + echo "Using delay-after-completion: $delay" > + sysfs_race_kernfs_kernfs_fop_write_iter 0030 before_mutex 1 $delay > + done > +} > + > +sysfs_test_0031() > +{ > + for delay in 0 2 4 8 16 32 64 128 246 512 1024; do > + echo "Using delay-after-completion: $delay" > + sysfs_race_kernfs_kernfs_fop_write_iter 0031 after_mutex 1 $delay > + done > +} > + > +# A write only succeeds *iff* a module removal happens *after* the > +# kernfs active reference is obtained with kernfs_get_active(). > +sysfs_test_0032() > +{ > + for delay in 0 2 4 8 16 32 64 128 246 512 1024; do > + echo "Using delay-after-completion: $delay" > + sysfs_race_kernfs_kernfs_fop_write_iter 0032 after_active 0 $delay > + done > +} > + > test_gen_desc() > { > echo -n "$1 x $(get_test_count $1)" > @@ -1013,6 +1184,10 @@ list_tests() > echo "$(test_gen_desc 0026) - block test writing y larger delay and resetting device" > echo "$(test_gen_desc 0027) - test rmmod deadlock while writing x ... " > echo "$(test_gen_desc 0028) - test rmmod deadlock using rtnl_lock while writing x ..." > + echo "$(test_gen_desc 0029) - racing removal of store op with kernfs at start" > + echo "$(test_gen_desc 0030) - racing removal of store op with kernfs before mutex" > + echo "$(test_gen_desc 0031) - racing removal of store op with kernfs after mutex" > + echo "$(test_gen_desc 0032) - racing removal of store op with kernfs after active" > } > > usage() > -- > 2.30.2 > -- Kees Cook
