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Message-ID: <se2nci5ftb2s53or6ysbgvtgcvvqwudxxzg3lbrxjm3y5mpo5o@y7k77ck3rz3k>
Date: Wed, 12 Mar 2025 22:23:32 +0100
From: Joel Granados <joel.granados@...nel.org>
To: John Sperbeck <jsperbeck@...gle.com>
Cc: Kees Cook <kees@...nel.org>, Wen Yang <wen.yang@...ux.dev>,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v4] sysctl: expose sysctl_check_table for unit testing
and use it
On Tue, Jan 21, 2025 at 01:33:53PM -0800, John Sperbeck wrote:
> In commit b5ffbd139688 ("sysctl: move the extra1/2 boundary check
> of u8 to sysctl_check_table_array"), a kunit test was added that
> registers a sysctl table. If the test is run as a module, then a
> lingering reference to the module is left behind, and a 'sysctl -a'
> leads to a panic.
>
> This can be reproduced with these kernel config settings:
>
> CONFIG_KUNIT=y
> CONFIG_SYSCTL_KUNIT_TEST=m
>
> Then run these commands:
>
> modprobe sysctl-test
> rmmod sysctl-test
> sysctl -a
>
> The panic varies but generally looks something like this:
>
> BUG: unable to handle page fault for address: ffffa4571c0c7db4
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 100000067 P4D 100000067 PUD 100351067 PMD 114f5e067 PTE 0
> Oops: Oops: 0000 [#1] SMP NOPTI
> ... ... ...
> RIP: 0010:proc_sys_readdir+0x166/0x2c0
> ... ... ...
> Call Trace:
> <TASK>
> iterate_dir+0x6e/0x140
> __se_sys_getdents+0x6e/0x100
> do_syscall_64+0x70/0x150
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> Instead of fully registering a sysctl table, expose the underlying
> checking function and use it in the unit test.
>
> Fixes: b5ffbd139688 ("sysctl: move the extra1/2 boundary check of u8 to sysctl_check_table_array")
> Signed-off-by: John Sperbeck <jsperbeck@...gle.com>
> ---
>
> The Change from v3 to v4 is to make sure sysctl_check_table_test_helper_sz()
> is defined in the unusual case that the sysctl kunit test is enabled, but
> CONFIG_SYSCTL is disabled.
>
> fs/proc/proc_sysctl.c | 22 +++++++++++++++++-----
> include/linux/sysctl.h | 17 +++++++++++++++++
> kernel/sysctl-test.c | 9 ++++++---
> 3 files changed, 40 insertions(+), 8 deletions(-)
>
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 27a283d85a6e..2d3272826cc2 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1137,11 +1137,12 @@ static int sysctl_check_table_array(const char *path, const struct ctl_table *ta
> return err;
> }
>
> -static int sysctl_check_table(const char *path, struct ctl_table_header *header)
> +static int sysctl_check_table(const char *path, const struct ctl_table *table,
> + size_t table_size)
> {
> - const struct ctl_table *entry;
> + const struct ctl_table *entry = table;
> int err = 0;
> - list_for_each_table_entry(entry, header) {
> + for (size_t i = 0 ; i < table_size; ++i, entry++) {
This should be avoided as the traversal of the ctl_table should be
handled in one place (the list_for_each_table_entry macro)
> if (!entry->procname)
> err |= sysctl_err(path, entry, "procname is null");
> if ((entry->proc_handler == proc_dostring) ||
> @@ -1173,6 +1174,16 @@ static int sysctl_check_table(const char *path, struct ctl_table_header *header)
> return err;
> }
>
> +#if IS_ENABLED(CONFIG_KUNIT)
> +int sysctl_check_table_test_helper_sz(const char *path,
> + const struct ctl_table *table,
> + size_t table_size)
> +{
> + return sysctl_check_table(path, table, table_size);
> +}
> +EXPORT_SYMBOL(sysctl_check_table_test_helper_sz);
> +#endif /* CONFIG_KUNIT */
> +
> static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table_header *head)
> {
> struct ctl_table *link_table, *link;
> @@ -1372,6 +1383,9 @@ struct ctl_table_header *__register_sysctl_table(
> struct ctl_dir *dir;
> struct ctl_node *node;
>
> + if (sysctl_check_table(path, table, table_size))
> + return NULL;
> +
> header = kzalloc(sizeof(struct ctl_table_header) +
> sizeof(struct ctl_node)*table_size, GFP_KERNEL_ACCOUNT);
> if (!header)
> @@ -1379,8 +1393,6 @@ struct ctl_table_header *__register_sysctl_table(
>
> node = (struct ctl_node *)(header + 1);
> init_header(header, root, set, node, table, table_size);
> - if (sysctl_check_table(path, header))
> - goto fail;
>
> spin_lock(&sysctl_lock);
> dir = &set->dir;
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index 40a6ac6c9713..02acd3670bd2 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -288,4 +288,21 @@ static inline bool sysctl_is_alias(char *param)
> int sysctl_max_threads(const struct ctl_table *table, int write, void *buffer,
> size_t *lenp, loff_t *ppos);
>
> +#if IS_ENABLED(CONFIG_KUNIT)
> +#define sysctl_check_table_test_helper(path, table) \
> + sysctl_check_table_test_helper_sz(path, table, ARRAY_SIZE(table))
> +#ifdef CONFIG_SYSCTL
> +int sysctl_check_table_test_helper_sz(const char *path,
> + const struct ctl_table *table,
> + size_t table_size);
> +#else /* CONFIG_SYSCTL */
> +static inline int sysctl_check_table_test_helper_sz(const char *path,
> + const struct ctl_table *table,
> + size_t table_size)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_SYSCTL */
> +#endif /* CONFIG_KUNIT */
> +
> #endif /* _LINUX_SYSCTL_H */
> diff --git a/kernel/sysctl-test.c b/kernel/sysctl-test.c
> index 3ac98bb7fb82..247dd8536fc7 100644
> --- a/kernel/sysctl-test.c
> +++ b/kernel/sysctl-test.c
> @@ -410,9 +410,12 @@ static void sysctl_test_register_sysctl_sz_invalid_extra_value(
> },
> };
>
> - KUNIT_EXPECT_NULL(test, register_sysctl("foo", table_foo));
> - KUNIT_EXPECT_NULL(test, register_sysctl("foo", table_bar));
> - KUNIT_EXPECT_NOT_NULL(test, register_sysctl("foo", table_qux));
> + KUNIT_EXPECT_EQ(test, -EINVAL,
> + sysctl_check_table_test_helper("foo", table_foo));
> + KUNIT_EXPECT_EQ(test, -EINVAL,
> + sysctl_check_table_test_helper("foo", table_bar));
> + KUNIT_EXPECT_EQ(test, 0,
> + sysctl_check_table_test_helper("foo", table_qux));
This should all be in lib/tests_sysctl.c. We should remove all this
function from the kunit and add an equivalent one to lib/tests_sysctl.c
Best
> }
>
> static struct kunit_case sysctl_test_cases[] = {
> --
> 2.48.0.rc2.279.g1de40edade-goog
>
--
Joel Granados
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