On 2/25/23 18:07, Guenter Roeck wrote:
> On Mon, Feb 13, 2023 at 12:56:59PM -0600, Frank Rowand wrote:
>> Add tests to exercise the actions that occur when the reference count
>> of devicetree nodes decrement to zero and beyond. Decrementing to
>> zero triggers freeing memory allocated for the node.
>>
>> This commit will expose a pr_err() issue in of_node_release(), resulting
>> in some kernal warnings and stack traces.
>>
>> When scripts/dtc/of_unittest_expect processes the console messages,
>> it will also report related problems for EXPECT messages due to the
>> pr_err() issue:
>> ** missing EXPECT begin : 5
>> Signed-off-by: Frank Rowand <frowand.list@xxxxxxxxx>
>> ---
>>
>> There are checkpatch warnings. I have reviewed them and feel
>> they can be ignored.
>>
>> Stack traces from the pr_err() issue:
>>
>
> Unfortunately my test beds trigger a warning if they encounter a backtrace
> in a log. Trying to implement workarounds would be just too time consuming,
> so I had to disable OF_UNITTEST in my boot tests as consequence of this
> patch.
Thank you for letting me know about this.
I'll create a patch to make the default action be skip the tests that cause
a backtrace, and create a command line option to enable those tests. Then
you can resume your valuable testing and people like me can enable the extra
tests.
Hopefully the patch will be well received.
-Frank
>
> Guenter
>
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 1 at lib/refcount.c:25 kobject_get+0xa0/0xa4
>> refcount_t: addition on 0; use-after-free.
>> Modules linked in:
>> CPU: 0 PID: 1 Comm: swapper/0 Tainted: G N 6.2.0-rc1-00005-g774057a35a67 #21
>> Hardware name: Generic DT based system
>> unwind_backtrace from show_stack+0x10/0x14
>> show_stack from dump_stack_lvl+0x40/0x4c
>> dump_stack_lvl from __warn+0x7c/0x15c
>> __warn from warn_slowpath_fmt+0x98/0xcc
>> warn_slowpath_fmt from kobject_get+0xa0/0xa4
>> kobject_get from of_node_get+0x14/0x1c
>> of_node_get from of_fwnode_get+0x34/0x40
>> of_fwnode_get from fwnode_full_name_string+0x34/0xa0
>> fwnode_full_name_string from device_node_string+0x4dc/0x4f4
>> device_node_string from pointer+0x364/0x598
>> pointer from vsnprintf+0x1f8/0x3d0
>> vsnprintf from vprintk_store+0x134/0x410
>> vprintk_store from vprintk_emit+0x6c/0x234
>> vprintk_emit from vprintk_default+0x20/0x28
>> vprintk_default from _printk+0x30/0x60
>> _printk from of_node_release+0xb0/0xf4
>> of_node_release from kobject_put+0xc4/0x29c
>> kobject_put from of_unittest+0x256c/0x2eb8
>> of_unittest from do_one_initcall+0x4c/0x268
>> do_one_initcall from kernel_init_freeable+0x1b4/0x214
>> kernel_init_freeable from kernel_init+0x18/0x130
>> kernel_init from ret_from_fork+0x14/0x2c
>> Exception stack(0xf0821fb0 to 0xf0821ff8)
>> 1fa0: 00000000 00000000 00000000 00000000
>> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> ---[ end trace 0000000000000000 ]---
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 1 at lib/refcount.c:28 fwnode_full_name_string+0x8c/0xa0
>> refcount_t: underflow; use-after-free.
>> Modules linked in:
>> CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W N 6.2.0-rc1-00005-g774057a35a67 #21
>> Hardware name: Generic DT based system
>> unwind_backtrace from show_stack+0x10/0x14
>> show_stack from dump_stack_lvl+0x40/0x4c
>> dump_stack_lvl from __warn+0x7c/0x15c
>> __warn from warn_slowpath_fmt+0x98/0xcc
>> warn_slowpath_fmt from fwnode_full_name_string+0x8c/0xa0
>> fwnode_full_name_string from device_node_string+0x4dc/0x4f4
>> device_node_string from pointer+0x364/0x598
>> pointer from vsnprintf+0x1f8/0x3d0
>> vsnprintf from vprintk_store+0x134/0x410
>> vprintk_store from vprintk_emit+0x6c/0x234
>> vprintk_emit from vprintk_default+0x20/0x28
>> vprintk_default from _printk+0x30/0x60
>> _printk from of_node_release+0xb0/0xf4
>> of_node_release from kobject_put+0xc4/0x29c
>> kobject_put from of_unittest+0x256c/0x2eb8
>> of_unittest from do_one_initcall+0x4c/0x268
>> do_one_initcall from kernel_init_freeable+0x1b4/0x214
>> kernel_init_freeable from kernel_init+0x18/0x130
>> kernel_init from ret_from_fork+0x14/0x2c
>> Exception stack(0xf0821fb0 to 0xf0821ff8)
>> 1fa0: 00000000 00000000 00000000 00000000
>> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> ---[ end trace 0000000000000000 ]---
>> ------------[ cut here ]------------
>> WARNING: CPU: 0 PID: 1 at lib/refcount.c:22 kobject_get+0x8c/0xa4
>> refcount_t: saturated; leaking memory.
>> Modules linked in:
>> CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W N 6.2.0-rc1-00005-g774057a35a67 #21
>> Hardware name: Generic DT based system
>> unwind_backtrace from show_stack+0x10/0x14
>> show_stack from dump_stack_lvl+0x40/0x4c
>> dump_stack_lvl from __warn+0x7c/0x15c
>> __warn from warn_slowpath_fmt+0x98/0xcc
>> warn_slowpath_fmt from kobject_get+0x8c/0xa4
>> kobject_get from of_node_get+0x14/0x1c
>> of_node_get from of_fwnode_get+0x34/0x40
>> of_fwnode_get from fwnode_full_name_string+0x34/0xa0
>> fwnode_full_name_string from device_node_string+0x4dc/0x4f4
>> device_node_string from pointer+0x364/0x598
>> pointer from vsnprintf+0x1f8/0x3d0
>> vsnprintf from vscnprintf+0x10/0x24
>> vscnprintf from printk_sprint+0x18/0x194
>> printk_sprint from vprintk_store+0x378/0x410
>> vprintk_store from vprintk_emit+0x6c/0x234
>> vprintk_emit from vprintk_default+0x20/0x28
>> vprintk_default from _printk+0x30/0x60
>> _printk from of_node_release+0xb0/0xf4
>> of_node_release from kobject_put+0xc4/0x29c
>> kobject_put from of_unittest+0x256c/0x2eb8
>> of_unittest from do_one_initcall+0x4c/0x268
>> do_one_initcall from kernel_init_freeable+0x1b4/0x214
>> kernel_init_freeable from kernel_init+0x18/0x130
>> kernel_init from ret_from_fork+0x14/0x2c
>> Exception stack(0xf0821fb0 to 0xf0821ff8)
>> 1fa0: 00000000 00000000 00000000 00000000
>> 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> ---[ end trace 0000000000000000 ]---
>>
>>
>> drivers/of/dynamic.c | 14 +-
>> .../of/unittest-data/testcases_common.dtsi | 1 +
>> drivers/of/unittest-data/tests-lifecycle.dtsi | 8 +
>> drivers/of/unittest.c | 148 +++++++++++++++++-
>> 4 files changed, 168 insertions(+), 3 deletions(-)
>> create mode 100644 drivers/of/unittest-data/tests-lifecycle.dtsi
>>
>> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
>> index cd3821a6444f..becb80f762c8 100644
>> --- a/drivers/of/dynamic.c
>> +++ b/drivers/of/dynamic.c
>> @@ -332,7 +332,19 @@ void of_node_release(struct kobject *kobj)
>> /* We should never be releasing nodes that haven't been detached. */
>> if (!of_node_check_flag(node, OF_DETACHED)) {
>> pr_err("ERROR: Bad of_node_put() on %pOF\n", node);
>> - dump_stack();
>> +
>> + /*
>> + * of unittests will test this path. Do not print the stack
>> + * trace when the error is caused by unittest so that we do
>> + * not display what a normal developer might reasonably
>> + * consider a real bug.
>> + */
>> + if (!IS_ENABLED(CONFIG_OF_UNITTEST) ||
>> + strcmp(node->parent->full_name, "testcase-data")) {
>> + dump_stack();
>> + pr_err("ERROR: next of_node_put() on this node will result in a kboject warning 'refcount_t: underflow; use-after-free.'\n");
>> + }
>> +
>> return;
>> }
>> if (!of_node_check_flag(node, OF_DYNAMIC))
>> diff --git a/drivers/of/unittest-data/testcases_common.dtsi b/drivers/of/unittest-data/testcases_common.dtsi
>> index 19292bbb4cbb..e7887f2301c1 100644
>> --- a/drivers/of/unittest-data/testcases_common.dtsi
>> +++ b/drivers/of/unittest-data/testcases_common.dtsi
>> @@ -17,3 +17,4 @@ node-remove {
>> #include "tests-address.dtsi"
>> #include "tests-platform.dtsi"
>> #include "tests-overlay.dtsi"
>> +#include "tests-lifecycle.dtsi"
>> diff --git a/drivers/of/unittest-data/tests-lifecycle.dtsi b/drivers/of/unittest-data/tests-lifecycle.dtsi
>> new file mode 100644
>> index 000000000000..28509a8783a7
>> --- /dev/null
>> +++ b/drivers/of/unittest-data/tests-lifecycle.dtsi
>> @@ -0,0 +1,8 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +/ {
>> + testcase-data {
>> + refcount-node {
>> + };
>> + };
>> +};
>> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
>> index bc0f1e50a4be..db72e208819c 100644
>> --- a/drivers/of/unittest.c
>> +++ b/drivers/of/unittest.c
>> @@ -54,8 +54,9 @@ static struct unittest_results {
>> * Print the expected message only if the current loglevel will allow
>> * the actual message to print.
>> *
>> - * Do not use EXPECT_BEGIN() or EXPECT_END() for messages generated by
>> - * pr_debug().
>> + * Do not use EXPECT_BEGIN(), EXPECT_END(), EXPECT_NOT_BEGIN(), or
>> + * EXPECT_NOT_END() to report messages expected to be reported or not
>> + * reported by pr_debug().
>> */
>> #define EXPECT_BEGIN(level, fmt, ...) \
>> printk(level pr_fmt("EXPECT \\ : ") fmt, ##__VA_ARGS__)
>> @@ -63,6 +64,12 @@ static struct unittest_results {
>> #define EXPECT_END(level, fmt, ...) \
>> printk(level pr_fmt("EXPECT / : ") fmt, ##__VA_ARGS__)
>>
>> +#define EXPECT_NOT_BEGIN(level, fmt, ...) \
>> + printk(level pr_fmt("EXPECT_NOT \\ : ") fmt, ##__VA_ARGS__)
>> +
>> +#define EXPECT_NOT_END(level, fmt, ...) \
>> + printk(level pr_fmt("EXPECT_NOT / : ") fmt, ##__VA_ARGS__)
>> +
>> static void __init of_unittest_find_node_by_name(void)
>> {
>> struct device_node *np;
>> @@ -1488,6 +1495,7 @@ static int __init unittest_data_add(void)
>> struct device_node *next = np->sibling;
>>
>> np->parent = of_root;
>> + /* this will clear OF_DETACHED in np and children */
>> attach_node_and_children(np);
>> np = next;
>> }
>> @@ -2998,6 +3006,141 @@ static void __init of_unittest_overlay(void)
>> static inline void __init of_unittest_overlay(void) { }
>> #endif
>>
>> +static void __init of_unittest_lifecycle(void)
>> +{
>> + unsigned int refcount;
>> + int found_refcount_one = 0;
>> + int put_count = 0;
>> + struct device_node *np;
>> + struct device_node *prev_sibling, *next_sibling;
>> + const char *refcount_path = "/testcase-data/refcount-node";
>> + const char *refcount_parent_path = "/testcase-data";
>> +
>> + /*
>> + * Node lifecycle tests, non-dynamic node:
>> + *
>> + * - Decrementing refcount to zero via of_node_put() should cause the
>> + * attempt to free the node memory by of_node_release() to fail
>> + * because the node is not a dynamic node.
>> + *
>> + * - Decrementing refcount past zero should result in additional
>> + * errors reported.
>> + */
>> +
>> + np = of_find_node_by_path(refcount_path);
>> + unittest(np, "find refcount_path \"%s\"\n", refcount_path);
>> + if (np == NULL)
>> + goto out_skip_tests;
>> +
>> + while (!found_refcount_one) {
>> +
>> + if (put_count++ > 10) {
>> + unittest(0, "guardrail to avoid infinite loop\n");
>> + goto out_skip_tests;
>> + }
>> +
>> + refcount = kref_read(&np->kobj.kref);
>> + if (refcount == 1)
>> + found_refcount_one = 1;
>> + else
>> + of_node_put(np);
>> + }
>> +
>> + EXPECT_BEGIN(KERN_INFO, "OF: ERROR: of_node_release() detected bad of_node_put() on /testcase-data/refcount-node");
>> +
>> + /*
>> + * refcount is now one, decrementing to zero will result in a call to
>> + * of_node_release() to free the node's memory, which should result
>> + * in an error
>> + */
>> + unittest(1, "/testcase-data/refcount-node is one");
>> + of_node_put(np);
>> +
>> + EXPECT_END(KERN_INFO, "OF: ERROR: of_node_release() detected bad of_node_put() on /testcase-data/refcount-node");
>> +
>> +
>> + /*
>> + * expect stack trace for subsequent of_node_put():
>> + * __refcount_sub_and_test() calls:
>> + * refcount_warn_saturate(r, REFCOUNT_SUB_UAF)
>> + *
>> + * Not capturing entire WARN_ONCE() trace with EXPECT_*(), just
>> + * the first three lines, and the last line.
>> + */
>> + EXPECT_BEGIN(KERN_INFO, "------------[ cut here ]------------");
>> + EXPECT_BEGIN(KERN_INFO, "WARNING: <<all>>");
>> + EXPECT_BEGIN(KERN_INFO, "refcount_t: underflow; use-after-free.");
>> + EXPECT_BEGIN(KERN_INFO, "---[ end trace <<int>> ]---");
>> +
>> + /* refcount is now zero, this should fail */
>> + unittest(1, "/testcase-data/refcount-node is zero");
>> + of_node_put(np);
>> +
>> + EXPECT_END(KERN_INFO, "---[ end trace <<int>> ]---");
>> + EXPECT_END(KERN_INFO, "refcount_t: underflow; use-after-free.");
>> + EXPECT_END(KERN_INFO, "WARNING: <<all>>");
>> + EXPECT_END(KERN_INFO, "------------[ cut here ]------------");
>> +
>> + /*
>> + * Q. do we expect to get yet another warning?
>> + * A. no, the WARNING is from WARN_ONCE()
>> + */
>> + EXPECT_NOT_BEGIN(KERN_INFO, "------------[ cut here ]------------");
>> + EXPECT_NOT_BEGIN(KERN_INFO, "WARNING: <<all>>");
>> + EXPECT_NOT_BEGIN(KERN_INFO, "refcount_t: underflow; use-after-free.");
>> + EXPECT_NOT_BEGIN(KERN_INFO, "---[ end trace <<int>> ]---");
>> +
>> + unittest(1, "/testcase-data/refcount-node is zero, second time");
>> + of_node_put(np);
>> +
>> + EXPECT_NOT_END(KERN_INFO, "---[ end trace <<int>> ]---");
>> + EXPECT_NOT_END(KERN_INFO, "refcount_t: underflow; use-after-free.");
>> + EXPECT_NOT_END(KERN_INFO, "WARNING: <<all>>");
>> + EXPECT_NOT_END(KERN_INFO, "------------[ cut here ]------------");
>> +
>> + /*
>> + * refcount of zero will trigger stack traces from any further
>> + * attempt to of_node_get() node "refcount-node". One example of
>> + * this is where of_unittest_check_node_linkage() will recursively
>> + * scan the tree, with 'for_each_child_of_node()' doing an
>> + * of_node_get() of the children of a node.
>> + *
>> + * Prevent the stack trace by removing node "refcount-node" from
>> + * its parent's child list.
>> + *
>> + * WARNING: EVIL, EVIL, EVIL:
>> + *
>> + * Directly manipulate the child list of node /testcase-data to
>> + * remove child refcount-node. This is ignoring all proper methods
>> + * of removing a child and will leak a small amount of memory.
>> + */
>> +
>> + np = of_find_node_by_path(refcount_parent_path);
>> + unittest(np, "find refcount_parent_path \"%s\"\n", refcount_parent_path);
>> + unittest(np, "ERROR: devicetree live tree left in a 'bad state' if test fail\n");
>> + if (np == NULL)
>> + return;
>> +
>> + prev_sibling = np->child;
>> + next_sibling = prev_sibling->sibling;
>> + if (!strcmp(prev_sibling->full_name, "refcount-node")) {
>> + np->child = next_sibling;
>> + next_sibling = next_sibling->sibling;
>> + }
>> + while (next_sibling) {
>> + if (!strcmp(next_sibling->full_name, "refcount-node"))
>> + prev_sibling->sibling = next_sibling->sibling;
>> + prev_sibling = next_sibling;
>> + next_sibling = next_sibling->sibling;
>> + }
>> + of_node_put(np);
>> +
>> + return;
>> +
>> +out_skip_tests:
>> + unittest(0, "One or more lifecycle tests skipped\n");
>> +}
>> +
>> #ifdef CONFIG_OF_OVERLAY
>>
>> /*
>> @@ -3502,6 +3645,7 @@ static int __init of_unittest(void)
>> of_unittest_match_node();
>> of_unittest_platform_populate();
>> of_unittest_overlay();
>> + of_unittest_lifecycle();
>>
>> /* Double check linkage after removing testcase data */
>> of_unittest_check_tree_linkage();
>> --
>> Frank Rowand <frowand.list@xxxxxxxxx>
>>
