From: Kees Cook <keescook@chromium.org>

Date: Wed, 4 Jan 2023 13:09:12 -0800

Subject: [PATCH] ext4: Fix function prototype mismatch for ext4_feat_ktype

References: bsc#1012628

Patch-mainline: 6.2.1

Git-commit: 118901ad1f25d2334255b3d50512fa20591531cd

commit 118901ad1f25d2334255b3d50512fa20591531cd upstream.

With clang's kernel control flow integrity (kCFI, CONFIG_CFI_CLANG),

indirect call targets are validated against the expected function

pointer prototype to make sure the call target is valid to help mitigate

ROP attacks. If they are not identical, there is a failure at run time,

which manifests as either a kernel panic or thread getting killed.

ext4_feat_ktype was setting the "release" handler to "kfree", which

doesn't have a matching function prototype. Add a simple wrapper

with the correct prototype.

This was found as a result of Clang's new -Wcast-function-type-strict

flag, which is more sensitive than the simpler -Wcast-function-type,

which only checks for type width mismatches.

Note that this code is only reached when ext4 is a loadable module and

it is being unloaded:

 CFI failure at kobject_put+0xbb/0x1b0 (target: kfree+0x0/0x180; expected type: 0x7c4aa698)

 ...

 RIP: 0010:kobject_put+0xbb/0x1b0

 ...

 Call Trace:

  <TASK>

  ext4_exit_sysfs+0x14/0x60 [ext4]

  cleanup_module+0x67/0xedb [ext4]

Fixes: b99fee58a20a ("ext4: create ext4_feat kobject dynamically")

Cc: Theodore Ts'o <tytso@mit.edu>

Cc: Eric Biggers <ebiggers@kernel.org>

Cc: stable@vger.kernel.org

Build-tested-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

Link: https://lore.kernel.org/r/20230103234616.never.915-kees@kernel.org

Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Eric Biggers <ebiggers@google.com>

Link: https://lore.kernel.org/r/20230104210908.gonna.388-kees@kernel.org

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Jiri Slaby <jslaby@suse.cz>

---

 fs/ext4/sysfs.c | 7 ++++++-

 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c

index d233c24e..e2b8b343 100644

--- a/fs/ext4/sysfs.c

+++ b/fs/ext4/sysfs.c

@@ -491,6 +491,11 @@ static void ext4_sb_release(struct kobject *kobj)

 	complete(&sbi->s_kobj_unregister);

 }

+static void ext4_feat_release(struct kobject *kobj)

+{

+	kfree(kobj);

+}

+

 static const struct sysfs_ops ext4_attr_ops = {

 	.show	= ext4_attr_show,

 	.store	= ext4_attr_store,

@@ -505,7 +510,7 @@ static struct kobj_type ext4_sb_ktype = {

 static struct kobj_type ext4_feat_ktype = {

 	.default_groups = ext4_feat_groups,

 	.sysfs_ops	= &ext4_attr_ops,

-	.release	= (void (*)(struct kobject *))kfree,

+	.release	= ext4_feat_release,

 };

 void ext4_notify_error_sysfs(struct ext4_sb_info *sbi)

-- 

2.35.3