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    SubjectRe: [PATCH] drivers: binderfs: fix memory leak in binderfs_fill_super
    On Fri, Aug 12, 2022 at 09:56:46PM +0800, Dongliang Mu wrote:
    > On Fri, Aug 12, 2022 at 9:41 PM Greg Kroah-Hartman
    > <gregkh@linuxfoundation.org> wrote:
    > >
    > > On Fri, Aug 12, 2022 at 09:21:24PM +0800, Dongliang Mu wrote:
    > > > From: Dongliang Mu <mudongliangabcd@gmail.com>
    > > >
    > > > In binderfs_fill_super, if s_root is not successfully initialized by
    > > > d_make_root, the previous allocated s_sb_info will not be freed since
    > > > generic_shutdown_super first checks if sb->s_root and then does
    > > > put_super operation. The put_super operation calls binderfs_put_super
    > > > to deallocate s_sb_info and put ipc_ns. This will lead to memory leak
    > > > in binderfs_fill_super.
    > > >
    > > > Fix this by invoking binderfs_put_super at error sites before s_root
    > > > is successfully initialized.
    > > >
    > > > Fixes: 095cf502b31e ("binderfs: port to new mount api")
    > > > Reported-by: syzkaller <syzkaller@googlegroups.com>
    > >
    > > Where is the specific syzkaller link for this report? It would be good
    > > to reference it so it can be properly checked.
    > >
    > > Also, how did you test this change?
    >
    > I found this memory leak in my local syzkaller, and there is no any
    > syzbot report about this crash, therefore I use such a Reported-by to
    > indicate.
    >
    > Although my local syzkaller does generate any reproducer, this bug can
    > be triggered by injecting faults at new_inode and d_make_root (i.e.,
    > between s_sb_info allocation and code after d_make_root).
    >
    > >
    > > > Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
    > > > ---
    > > > drivers/android/binderfs.c | 8 ++++++--
    > > > 1 file changed, 6 insertions(+), 2 deletions(-)
    > > >
    > > > diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
    > > > index 588d753a7a19..20f5bc77495f 100644
    > > > --- a/drivers/android/binderfs.c
    > > > +++ b/drivers/android/binderfs.c
    > > > @@ -710,8 +710,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
    > > > info->mount_opts.stats_mode = ctx->stats_mode;
    > > >
    > > > inode = new_inode(sb);
    > > > - if (!inode)
    > > > + if (!inode) {
    > > > + binderfs_put_super(sb);
    > > > return -ENOMEM;
    > > > + }
    > > >
    > > > inode->i_ino = FIRST_INODE;
    > > > inode->i_fop = &simple_dir_operations;
    > > > @@ -721,8 +723,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
    > > > set_nlink(inode, 2);
    > > >
    > > > sb->s_root = d_make_root(inode);
    > > > - if (!sb->s_root)
    > > > + if (!sb->s_root) {
    > > > + binderfs_put_super(sb);
    > > > return -ENOMEM;
    > > > + }
    > >
    > > How did you test this change to verify that you are not now just leaking
    > > memory? It looks to me like you just changed one problem for another
    > > one :(
    >
    > As mentioned above, I just tested my change by injecting faults at
    > new_inode and d_make_root.
    >
    > Can you explain more about "changed one problem for another one"? I
    > don't quite understand this statement.

    I think you are leaking memory in at least your second change here,
    possibly the first, I didn't look at the code very closely.

    So please verify that you do not add problems when trying to remove
    them.

    Also, really, in a normal system, this path is impossible to hit.

    thanks,

    greg k-h

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