[PATCH 0/4] firmware: qemu_fw_cfg: misc bug fixes

[PATCH 0/4] firmware: qemu_fw_cfg: misc bug fixes

[Johan Hovold]

When searching for the latest umn.edu patches I stumbled upon a recently
submitted fix for a bug purportedly introduced by umn.edu:

	https://lore.kernel.org/r/YaZc4LbX5hrJDnec@hovoldconsulting.com

The patch in question is obviously bogus, but a closer look at the
function in question revealed a number of other bugs, including one that
was indeed introduced by umn.edu but that was missed during the
(re-)review.

Included is also a related clean up.

Johan


Johan Hovold (4):
  firmware: qemu_fw_cfg: fix NULL-pointer deref on duplicate entries
  firmware: qemu_fw_cfg: fix kobject leak in probe error path
  firmware: qemu_fw_cfg: fix sysfs information leak
  firmware: qemu_fw_cfg: remove sysfs entries explicitly

 drivers/firmware/qemu_fw_cfg.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

-- 
2.32.0

[PATCH 1/4] firmware: qemu_fw_cfg: fix NULL-pointer deref on duplicate entries

[Johan Hovold]

Commit fe3c60684377 ("firmware: Fix a reference count leak.") "fixed"
a kobject leak in the file registration helper by properly calling
kobject_put() for the entry in case registration of the object fails
(e.g. due to a name collision).

This would however result in a NULL pointer dereference when the
release function tries to remove the never added entry from the
fw_cfg_entry_cache list.

Fix this by moving the list-removal out of the release function.

Note that the offending commit was one of the benign looking umn.edu
fixes which was reviewed but not reverted. [1][2]

[1] https://lore.kernel.org/r/202105051005.49BFABCE@keescook
[2] https://lore.kernel.org/all/YIg7ZOZvS3a8LjSv@kroah.com

Fixes: fe3c60684377 ("firmware: Fix a reference count leak.")
Cc: stable@vger.kernel.org      # 5.8
Cc: Qiushi Wu <wu000273@umn.edu>
Cc: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/firmware/qemu_fw_cfg.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 172c751a4f6c..a9c64ebfc49a 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -388,9 +388,7 @@ static void fw_cfg_sysfs_cache_cleanup(void)
 	struct fw_cfg_sysfs_entry *entry, *next;
 
 	list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
-		/* will end up invoking fw_cfg_sysfs_cache_delist()
-		 * via each object's release() method (i.e. destructor)
-		 */
+		fw_cfg_sysfs_cache_delist(entry);
 		kobject_put(&entry->kobj);
 	}
 }
@@ -448,7 +446,6 @@ static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
 {
 	struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
 
-	fw_cfg_sysfs_cache_delist(entry);
 	kfree(entry);
 }
 
-- 
2.32.0

[PATCH 2/4] firmware: qemu_fw_cfg: fix kobject leak in probe error path

[Johan Hovold]

An initialised kobject must be freed using kobject_put() to avoid
leaking associated resources (e.g. the object name).

Commit fe3c60684377 ("firmware: Fix a reference count leak.") "fixed"
the leak in the first error path of the file registration helper but
left the second one unchanged. This "fix" would however result in a NULL
pointer dereference due to the release function also removing the never
added entry from the fw_cfg_entry_cache list. This has now been
addressed.

Fix the remaining kobject leak by restoring the common error path and
adding the missing kobject_put().

Fixes: 75f3e8e47f38 ("firmware: introduce sysfs driver for QEMU's fw_cfg device")
Cc: stable@vger.kernel.org      # 4.6
Cc: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/firmware/qemu_fw_cfg.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index a9c64ebfc49a..ccb7ed62452f 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -603,15 +603,13 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f)
 	/* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
 	err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
 				   fw_cfg_sel_ko, "%d", entry->select);
-	if (err) {
-		kobject_put(&entry->kobj);
-		return err;
-	}
+	if (err)
+		goto err_put_entry;
 
 	/* add raw binary content access */
 	err = sysfs_create_bin_file(&entry->kobj, &fw_cfg_sysfs_attr_raw);
 	if (err)
-		goto err_add_raw;
+		goto err_del_entry;
 
 	/* try adding "/sys/firmware/qemu_fw_cfg/by_name/" symlink */
 	fw_cfg_build_symlink(fw_cfg_fname_kset, &entry->kobj, entry->name);
@@ -620,9 +618,10 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f)
 	fw_cfg_sysfs_cache_enlist(entry);
 	return 0;
 
-err_add_raw:
+err_del_entry:
 	kobject_del(&entry->kobj);
-	kfree(entry);
+err_put_entry:
+	kobject_put(&entry->kobj);
 	return err;
 }
 
-- 
2.32.0

[PATCH 3/4] firmware: qemu_fw_cfg: fix sysfs information leak

[Johan Hovold]

Make sure to always NUL-terminate file names retrieved from the firmware
to avoid accessing data beyond the entry slab buffer and exposing it
through sysfs in case the firmware data is corrupt.

Fixes: 75f3e8e47f38 ("firmware: introduce sysfs driver for QEMU's fw_cfg device")
Cc: stable@vger.kernel.org      # 4.6
Cc: Gabriel Somlo <somlo@cmu.edu>
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/firmware/qemu_fw_cfg.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index ccb7ed62452f..f08e056ed0ae 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -598,7 +598,7 @@ static int fw_cfg_register_file(const struct fw_cfg_file *f)
 	/* set file entry information */
 	entry->size = be32_to_cpu(f->size);
 	entry->select = be16_to_cpu(f->select);
-	memcpy(entry->name, f->name, FW_CFG_MAX_FILE_PATH);
+	strscpy(entry->name, f->name, FW_CFG_MAX_FILE_PATH);
 
 	/* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
 	err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
-- 
2.32.0

[PATCH 4/4] firmware: qemu_fw_cfg: remove sysfs entries explicitly

[Johan Hovold]

Explicitly remove the file entries from sysfs before dropping the final
reference for symmetry reasons and for consistency with the rest of the
driver.

Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/firmware/qemu_fw_cfg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index f08e056ed0ae..b436342115af 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -389,6 +389,7 @@ static void fw_cfg_sysfs_cache_cleanup(void)
 
 	list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
 		fw_cfg_sysfs_cache_delist(entry);
+		kobject_del(&entry->kobj);
 		kobject_put(&entry->kobj);
 	}
 }
-- 
2.32.0