[PATCH v1] hfsplus: fix memory leak on mount failure

[Swaraj Gaikwad <swarajgaikwad1925@gmail.com>]

syzbot reported a memory leak in the hfsplus mount path when the mount
fails, which occurs because the fs_context API moves ownership of
fc->s_fs_info to sb->s_fs_info early in sget_fc().

When filesystems are mounted using the new API, the VFS (specifically
sget_fc) transfers the ownership of the context's s_fs_info (the 'sbi'
struct) to the superblock (sb->s_fs_info) and clears the context
pointer.

If the mount fails after this transfer the VFS calls
deactivate_locked_super, which invokes the filesystem's kill_sb
callback. Previously, hfsplus used the generic kill_block_super, which
does not free sb->s_fs_info, resulting in the 'sbi' structure and its
loaded NLS tables being leaked.

Fix this by implementing a filesystem-specific ->kill_sb() that frees
sb->s_fs_info and its NLS resources before calling kill_block_super().
Also remove the early kfree(sbi) from hfsplus_fill_super()’s error path,
because the superblock unconditionally owns s_fs_info when using the
fs_context API.

Testing:
This fix was verified by building the kernel with the .config provided
by the syzkaller reporter and running the reproducer. The reproducer
now runs successfully without triggering any memory leaks or kernel errors.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git e69c7c175115

Reported-by: syzbot+99f6ed51479b86ac4c41@syzkaller.appspotmail.com
Signed-off-by: Swaraj Gaikwad <swarajgaikwad1925@gmail.com>
---
 fs/hfsplus/super.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/hfsplus/super.c b/fs/hfsplus/super.c
index 16bc4abc67e0..fa7420d08da1 100644
--- a/fs/hfsplus/super.c
+++ b/fs/hfsplus/super.c
@@ -629,7 +629,6 @@ static int hfsplus_fill_super(struct super_block *sb, struct fs_context *fc)
 out_unload_nls:
 	unload_nls(sbi->nls);
 	unload_nls(nls);
-	kfree(sbi);
 	return err;
 }

@@ -688,10 +687,23 @@ static int hfsplus_init_fs_context(struct fs_context *fc)
 	return 0;
 }

+static void hfsplus_kill_sb(struct super_block *sb)
+{
+    struct hfsplus_sb_info *sbi = HFSPLUS_SB(sb);
+
+    if (sbi) {
+        unload_nls(sbi->nls);
+        kfree(sbi);
+        sb->s_fs_info = NULL;
+    }
+
+    kill_block_super(sb);
+}
+
 static struct file_system_type hfsplus_fs_type = {
 	.owner		= THIS_MODULE,
 	.name		= "hfsplus",
-	.kill_sb	= kill_block_super,
+	.kill_sb	= hfsplus_kill_sb,
 	.fs_flags	= FS_REQUIRES_DEV,
 	.init_fs_context = hfsplus_init_fs_context,
 };

base-commit: 6bda50f4333fa61c07f04f790fdd4e2c9f4ca610
--
2.52.0