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: 7feebfa487b92 ("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 --- lib/test_firmware.c | 52 ++++++++++++++++++++++++++++++--------------- 1 file changed, 35 insertions(+), 17 deletions(-)

diff --git a/lib/test_firmware.c b/lib/test_firmware.c index 05ed84c2fc4c..35417e0af3f4 100644 --- a/lib/test_firmware.c +++ b/lib/test_firmware.c @@ -353,16 +353,26 @@ static ssize_t config_test_show_str(char *dst, return len; }

-static int test_dev_config_update_bool(const char *buf, size_t size, +static inline int __test_dev_config_update_bool(const char *buf, size_t size, bool *cfg) { int ret;

- mutex_lock(&test_fw_mutex); if (kstrtobool(buf, cfg) < 0) ret = -EINVAL; else ret = size; + + return ret; +} + +static int test_dev_config_update_bool(const char *buf, size_t size, + bool *cfg) +{ + int ret; + + mutex_lock(&test_fw_mutex); + ret = __test_dev_config_update_bool(buf, size, cfg); mutex_unlock(&test_fw_mutex);

return ret; @@ -373,7 +383,8 @@ static ssize_t test_dev_config_show_bool(char *buf, bool val) return snprintf(buf, PAGE_SIZE, "%d\n", val); }

-static int test_dev_config_update_size_t(const char *buf, +static int __test_dev_config_update_size_t( + const char *buf, size_t size, size_t *cfg) { @@ -384,9 +395,7 @@ static int test_dev_config_update_size_t(const char *buf, if (ret) return ret;

- mutex_lock(&test_fw_mutex); *(size_t *)cfg = new; - mutex_unlock(&test_fw_mutex);

/* Always return full write size even if we didn't consume all */ return size; @@ -402,7 +411,7 @@ static ssize_t test_dev_config_show_int(char *buf, int val) return snprintf(buf, PAGE_SIZE, "%d\n", val); }

-static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg) +static int __test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg) { u8 val; int ret; @@ -411,14 +420,23 @@ static int test_dev_config_update_u8(const char *buf, size_t size, u8 *cfg) 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 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; +} + static ssize_t test_dev_config_show_u8(char *buf, u8 val) { return snprintf(buf, PAGE_SIZE, "%u\n", val); @@ -471,10 +489,10 @@ static ssize_t config_num_requests_store(struct device *dev, 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); + rc = __test_dev_config_update_u8(buf, count, + &test_fw_config->num_requests); + mutex_unlock(&test_fw_mutex);

out: return rc; @@ -518,10 +536,10 @@ static ssize_t config_buf_size_store(struct device *dev, mutex_unlock(&test_fw_mutex); goto out; } - mutex_unlock(&test_fw_mutex);

- rc = test_dev_config_update_size_t(buf, count, - &test_fw_config->buf_size); + rc = __test_dev_config_update_size_t(buf, count, + &test_fw_config->buf_size); + mutex_unlock(&test_fw_mutex);

out: return rc; @@ -548,10 +566,10 @@ static ssize_t config_file_offset_store(struct device *dev, mutex_unlock(&test_fw_mutex); goto out; } - mutex_unlock(&test_fw_mutex);

- rc = test_dev_config_update_size_t(buf, count, - &test_fw_config->file_offset); + rc = __test_dev_config_update_size_t(buf, count, + &test_fw_config->file_offset); + mutex_unlock(&test_fw_mutex);

out: return rc;