Messages in this thread | | | Date | Thu, 24 Mar 2022 19:19:40 +0100 | From | David Sterba <> | Subject | Re: [PATCH] fs: btrfs: fix possible use-after-free bug in error handling code of btrfs_get_root_ref() |
| |
On Thu, Mar 24, 2022 at 06:44:54AM -0700, Jia-Ju Bai wrote: > In btrfs_get_root_ref(), when btrfs_insert_fs_root() fails, > btrfs_put_root() will be called to possibly free the memory area of > the variable root. However, this variable is then used again in error > handling code after "goto fail", when ret is not -EEXIST. > > To fix this possible bug, btrfs_put_root() is only called when ret is > -EEXIST for "goto again". > > Reported-by: TOTE Robot <oslab@tsinghua.edu.cn> > Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> > --- > fs/btrfs/disk-io.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index b30309f187cf..126f244cdf88 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -1850,9 +1850,10 @@ static struct btrfs_root *btrfs_get_root_ref(struct btrfs_fs_info *fs_info, > > ret = btrfs_insert_fs_root(fs_info, root); > if (ret) { > - btrfs_put_root(root); > - if (ret == -EEXIST) > + if (ret == -EEXIST) { > + btrfs_put_root(root);
I think this fix is correct, though it's not that clear. If you look how the code changed, there was the unconditional put and then followed by a free:
8c38938c7bb0 ("btrfs: move the root freeing stuff into btrfs_put_root")
Here it's putting twice where one will be the final free.
And then the whole refcounting gets updated in
4785e24fa5d2 ("btrfs: don't take an extra root ref at allocation time")
which could be removing the wrong put, I'm not yet sure.
| |