Hi,
This will lead a compile error.
arch/powerpc/platforms/powernv/opal-dump.c: In function ??process_dump??:
arch/powerpc/platforms/powernv/opal-dump.c:409:7: error: void value not
ignored as it ought to be
dump = create_dump_obj(dump_id, dump_size, dump_type);
^
make[2]: *** [arch/powerpc/platforms/powernv/opal-dump.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [arch/powerpc/platforms/powernv] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [arch/powerpc/platforms] Error 2
make: *** Waiting for unfinished jobs....
?? 2020/10/26 13:57, Sasha Levin ะด??:
> This is a note to let you know that I've just added the patch titled
>
> powerpc/powernv/dump: Fix race while processing OPAL dump
>
> to the 4.4-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> powerpc-powernv-dump-fix-race-while-processing-opal-.patch
> and it can be found in the queue-4.4 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <[email protected]> know about it.
>
>
>
> commit faa63b3cf39346b7a1e96d128133aadd8b59cc4a
> Author: Vasant Hegde <[email protected]>
> Date: Sat Oct 17 22:12:10 2020 +0530
>
> powerpc/powernv/dump: Fix race while processing OPAL dump
>
> [ Upstream commit 0a43ae3e2beb77e3481d812834d33abe270768ab ]
>
> Every dump reported by OPAL is exported to userspace through a sysfs
> interface and notified using kobject_uevent(). The userspace daemon
> (opal_errd) then reads the dump and acknowledges that the dump is
> saved safely to disk. Once acknowledged the kernel removes the
> respective sysfs file entry causing respective resources to be
> released including kobject.
>
> However it's possible the userspace daemon may already be scanning
> dump entries when a new sysfs dump entry is created by the kernel.
> User daemon may read this new entry and ack it even before kernel can
> notify userspace about it through kobject_uevent() call. If that
> happens then we have a potential race between
> dump_ack_store->kobject_put() and kobject_uevent which can lead to
> use-after-free of a kernfs object resulting in a kernel crash.
>
> This patch fixes this race by protecting the sysfs file
> creation/notification by holding a reference count on kobject until we
> safely send kobject_uevent().
>
> The function create_dump_obj() returns the dump object which if used
> by caller function will end up in use-after-free problem again.
> However, the return value of create_dump_obj() function isn't being
> used today and there is no need as well. Hence change it to return
> void to make this fix complete.
>
> Fixes: c7e64b9ce04a ("powerpc/powernv Platform dump interface")
> Signed-off-by: Vasant Hegde <[email protected]>
> Signed-off-by: Michael Ellerman <[email protected]>
> Link: https://lore.kernel.org/r/[email protected]
> Signed-off-by: Sasha Levin <[email protected]>
>
> diff --git a/arch/powerpc/platforms/powernv/opal-dump.c b/arch/powerpc/platforms/powernv/opal-dump.c
> index 4c827826c05eb..e21e2c0af69d2 100644
> --- a/arch/powerpc/platforms/powernv/opal-dump.c
> +++ b/arch/powerpc/platforms/powernv/opal-dump.c
> @@ -319,15 +319,14 @@ static ssize_t dump_attr_read(struct file *filep, struct kobject *kobj,
> return count;
> }
>
> -static struct dump_obj *create_dump_obj(uint32_t id, size_t size,
> - uint32_t type)
> +static void create_dump_obj(uint32_t id, size_t size, uint32_t type)
> {
> struct dump_obj *dump;
> int rc;
>
> dump = kzalloc(sizeof(*dump), GFP_KERNEL);
> if (!dump)
> - return NULL;
> + return;
>
> dump->kobj.kset = dump_kset;
>
> @@ -347,21 +346,39 @@ static struct dump_obj *create_dump_obj(uint32_t id, size_t size,
> rc = kobject_add(&dump->kobj, NULL, "0x%x-0x%x", type, id);
> if (rc) {
> kobject_put(&dump->kobj);
> - return NULL;
> + return;
> }
>
> + /*
> + * As soon as the sysfs file for this dump is created/activated there is
> + * a chance the opal_errd daemon (or any userspace) might read and
> + * acknowledge the dump before kobject_uevent() is called. If that
> + * happens then there is a potential race between
> + * dump_ack_store->kobject_put() and kobject_uevent() which leads to a
> + * use-after-free of a kernfs object resulting in a kernel crash.
> + *
> + * To avoid that, we need to take a reference on behalf of the bin file,
> + * so that our reference remains valid while we call kobject_uevent().
> + * We then drop our reference before exiting the function, leaving the
> + * bin file to drop the last reference (if it hasn't already).
> + */
> +
> + /* Take a reference for the bin file */
> + kobject_get(&dump->kobj);
> rc = sysfs_create_bin_file(&dump->kobj, &dump->dump_attr);
> - if (rc) {
> + if (rc == 0) {
> + kobject_uevent(&dump->kobj, KOBJ_ADD);
> +
> + pr_info("%s: New platform dump. ID = 0x%x Size %u\n",
> + __func__, dump->id, dump->size);
> + } else {
> + /* Drop reference count taken for bin file */
> kobject_put(&dump->kobj);
> - return NULL;
> }
>
> - pr_info("%s: New platform dump. ID = 0x%x Size %u\n",
> - __func__, dump->id, dump->size);
> -
> - kobject_uevent(&dump->kobj, KOBJ_ADD);
> -
> - return dump;
> + /* Drop our reference */
> + kobject_put(&dump->kobj);
> + return;
> }
>
> static irqreturn_t process_dump(int irq, void *data)
> .
>