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firmware: qemu_fw_cfg: fix NULL-pointer deref on duplicate entries

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commit d3e305592d69e21e36b76d24ca3c01971a2d09be upstream.

Commit fe3c606843 ("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: fe3c606843 ("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>
Link: https://lore.kernel.org/r/20211201132528.30025-2-johan@kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Johan Hovold
2021-12-01 14:25:25 +01:00
committed by Greg Kroah-Hartman
parent ff9588cf15
commit 889c73305b
1 changed files with 1 additions and 4 deletions
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5
drivers/firmware/qemu_fw_cfg.c
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@@ -388,9 +388,7 @@ static void fw_cfg_sysfs_cache_cleanup(void)
struct fw_cfg_sysfs_entry *entry, *next; struct fw_cfg_sysfs_entry *entry, *next;
list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) { list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
/* will end up invoking fw_cfg_sysfs_cache_delist() fw_cfg_sysfs_cache_delist(entry);
* via each object's release() method (i.e. destructor)
*/
kobject_put(&entry->kobj); 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); struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
fw_cfg_sysfs_cache_delist(entry);
kfree(entry); kfree(entry);
} }