On Mon, Dec 2, 2024 at 3:01 PM Bernd Schubert <bschubert@xxxxxxx> wrote: > > In fuse_get_user_pages(), set *nbytesp to 0 when struct page **pages > allocation fails. This prevents the caller (fuse_direct_io) from making > incorrect assumptions that could lead to NULL pointer dereferences > when processing the request reply. > > Previously, *nbytesp was left unmodified on allocation failure, which > could cause issues if the caller assumed pages had been added to > ap->descs[] when they hadn't. > > Reported-by: syzbot+87b8e6ed25dbc41759f7@xxxxxxxxxxxxxxxxxxxxxxxxx > Closes: https://syzkaller.appspot.com/bug?extid=87b8e6ed25dbc41759f7 > Fixes: 3b97c3652d91 ("fuse: convert direct io to use folios") > Signed-off-by: Bernd Schubert <bschubert@xxxxxxx> > Reviewed-by: Joanne Koong <joannelkoong@xxxxxxxxx> > --- > Changes in v2: > - Set ret in the (!pages) condition only to avoid returning > ENOMEM when the while loop would not do anything > - Remove the error check in fuse_copy_do(), that is a bit debatable. > I had added it to prevent kernel crashes on fuse error, but then > it causes 'visual clutter' (Joanne) > - Link to v1: https://lore.kernel.org/r/20241202-fix-fuse_get_user_pages-v1-1-8b5cccaf5bbe@xxxxxxx > --- > fs/fuse/file.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 88d0946b5bc98705e0d895bc798aa4d9df080c3c..ae74d2b7ad5be14e4d157495e7c00fcf3fc40625 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -1541,8 +1541,10 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, > */ > struct page **pages = kzalloc(max_pages * sizeof(struct page *), > GFP_KERNEL); > - if (!pages) > - return -ENOMEM; > + if (!pages) { > + ret = -ENOMEM; > + goto out; > + } > > while (nbytes < *nbytesp && nr_pages < max_pages) { > unsigned nfolios, i; > @@ -1584,6 +1586,7 @@ static int fuse_get_user_pages(struct fuse_args_pages *ap, struct iov_iter *ii, > else > ap->args.out_pages = true; > > +out: > *nbytesp = nbytes; > > return ret < 0 ? ret : 0; > LGTM! Thanks, Joanne > --- > base-commit: e70140ba0d2b1a30467d4af6bcfe761327b9ec95 > change-id: 20241202-fix-fuse_get_user_pages-6a920cb04184 > > Best regards, > -- > Bernd Schubert <bschubert@xxxxxxx> >
