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List:       git-commits-head
Subject:    ext4: fix function prototype mismatch for ext4_feat_ktype
From:       Linux Kernel Mailing List <linux-kernel () vger ! kernel ! org>
Date:       2023-02-28 17:17:36
Message-ID: git-mailbomb-linux-master-d99a55a94a0db8eda4a336a6f21730b844b8d2d2 () kernel ! org
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Commit:     d99a55a94a0db8eda4a336a6f21730b844b8d2d2
Parent:     7fc51f923ea6b1c6f304789965414149eaedb358
Refname:    refs/heads/master
Web:        https://git.kernel.org/torvalds/c/d99a55a94a0db8eda4a336a6f21730b844b8d2d2
Author:     Kees Cook <keescook@chromium.org>
AuthorDate: Wed Jan 4 13:09:12 2023 -0800
Committer:  Theodore Ts'o <tytso@mit.edu>
CommitDate: Sun Feb 19 00:09:59 2023 -0500

    ext4: fix function prototype mismatch for ext4_feat_ktype
    
    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: Theodore Ts'o <tytso@mit.edu>
---
 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 d233c24ea3425..e2b8b3437c589 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)
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