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Mirsad Goran Todorovac 3127ab7eee test_firmware: prevent race conditions by a correct implementation of locking 
commit 4acfe3dfde upstream.

Dan Carpenter spotted a race condition in a couple of situations like
these in the test_firmware driver:

static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
{
        u8 val;
        int ret;

        ret = kstrtou8(buf, 10, &val);
        if (ret)
                return ret;

        mutex_lock(&test_fw_mutex);
        *(u8 *)cfg = val;
        mutex_unlock(&test_fw_mutex);

        /* Always return full write size even if we didn't consume all */
        return size;
}

static ssize_t config_num_requests_store(struct device *dev,
                                         struct device_attribute *attr,
                                         const char *buf, size_t count)
{
        int rc;

        mutex_lock(&test_fw_mutex);
        if (test_fw_config->reqs) {
                pr_err("Must call release_all_firmware prior to changing config\n");
                rc = -EINVAL;
                mutex_unlock(&test_fw_mutex);
                goto out;
        }
        mutex_unlock(&test_fw_mutex);

        rc = test_dev_config_update_u8(buf, count,
                                       &test_fw_config->num_requests);

out:
        return rc;
}

static ssize_t config_read_fw_idx_store(struct device *dev,
                                        struct device_attribute *attr,
                                        const char *buf, size_t count)
{
        return test_dev_config_update_u8(buf, count,
                                         &test_fw_config->read_fw_idx);
}

The function test_dev_config_update_u8() is called from both the locked
and the unlocked context, function config_num_requests_store() and
config_read_fw_idx_store() which can both be called asynchronously as
they are driver's methods, while test_dev_config_update_u8() and siblings
change their argument pointed to by u8 *cfg or similar pointer.

To avoid deadlock on test_fw_mutex, the lock is dropped before calling
test_dev_config_update_u8() and re-acquired within test_dev_config_update_u8()
itself, but alas this creates a race condition.

Having two locks wouldn't assure a race-proof mutual exclusion.

This situation is best avoided by the introduction of a new, unlocked
function __test_dev_config_update_u8() which can be called from the locked
context and reducing test_dev_config_update_u8() to:

static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg)
{
        int ret;

        mutex_lock(&test_fw_mutex);
        ret = __test_dev_config_update_u8(buf, size, cfg);
        mutex_unlock(&test_fw_mutex);

        return ret;
}

doing the locking and calling the unlocked primitive, which enables both
locked and unlocked versions without duplication of code.

The similar approach was applied to all functions called from the locked
and the unlocked context, which safely mitigates both deadlocks and race
conditions in the driver.

__test_dev_config_update_bool(), __test_dev_config_update_u8() and
__test_dev_config_update_size_t() unlocked versions of the functions
were introduced to be called from the locked contexts as a workaround
without releasing the main driver's lock and thereof causing a race
condition.

The test_dev_config_update_bool(), test_dev_config_update_u8() and
test_dev_config_update_size_t() locked versions of the functions
are being called from driver methods without the unnecessary multiplying
of the locking and unlocking code for each method, and complicating
the code with saving of the return value across lock.

Fixes: 7feebfa487 ("test_firmware: add support for request_firmware_into_buf")
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Russ Weight <russell.h.weight@intel.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Tianfei Zhang <tianfei.zhang@intel.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-kselftest@vger.kernel.org
Cc: stable@vger.kernel.org # v5.4
Suggested-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@alu.unizg.hr>
Link: https://lore.kernel.org/r/20230509084746.48259-1-mirsad.todorovac@alu.unizg.hr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-08-30 16:31:50 +02:00
arch powerpc/rtas_flash: allow user copy to flash block cache objects 2023-08-30 16:31:47 +02:00
block block: fix signed int overflow in Amiga partition support 2023-08-30 16:31:46 +02:00
certs certs/blacklist_hashes.c: fix const confusion in certs blacklist 2022-06-25 11:49:16 +02:00
crypto crypto: drbg - Only fail when jent is unavailable in FIPS mode 2023-05-17 11:13:13 +02:00
Documentation Documentation: security-bugs.rst: clarify CVE handling 2023-08-11 11:45:34 +02:00
drivers mmc: wbsd: fix double mmc_free_host() in wbsd_init() 2023-08-30 16:31:50 +02:00
firmware Fix built-in early-load Intel microcode alignment 2020-01-23 08:21:29 +01:00
fs cifs: Release folio lock on fscache read hit. 2023-08-30 16:31:50 +02:00
include net: do not allow gso_size to be set to GSO_BY_FRAGS 2023-08-30 16:31:49 +02:00
init init, x86: Move mem_encrypt_init() into arch_cpu_finalize_init() 2023-08-08 19:49:18 +02:00
ipc ipc/sem: Fix dangling sem_array access in semtimedop race 2022-12-08 11:18:35 +01:00
kernel perf: Fix function pointer case 2023-08-11 11:45:36 +02:00
lib test_firmware: prevent race conditions by a correct implementation of locking 2023-08-30 16:31:50 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm treewide: Remove uninitialized_var() usage 2023-08-11 11:45:01 +02:00
net sock: Fix misuse of sk_under_memory_pressure() 2023-08-30 16:31:49 +02:00
samples samples/bpf: Fix buffer overflow in tcp_basertt 2023-08-11 11:45:03 +02:00
scripts modpost: fix section mismatch message for R_ARM_{PC24,CALL,JUMP24} 2023-08-11 11:45:10 +02:00
security IMA: allow/fix UML builds 2023-08-30 16:31:43 +02:00
sound ALSA: usb-audio: Add support for Mythware XA001AU capture and playback interfaces. 2023-08-30 16:31:49 +02:00
tools selftests: mirror_gre_changes: Tighten up the TTL test match 2023-08-30 16:31:48 +02:00
usr initramfs: restore default compression behavior 2020-04-13 10:44:59 +02:00
virt KVM: arm64: vgic: Fix exit condition in scan_its_table() 2022-11-03 23:52:24 +09:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS clocksource/drivers: Unify the names to timer-* format 2023-08-11 11:45:02 +02:00
Makefile Linux 4.19.292 2023-08-16 18:13:01 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.