On Wed, Nov 6, 2024 at 3:43 AM Edward Adam Davis <eadavis@xxxxxx> wrote:
>
> On Mon, 4 Nov 2024 20:30:41 +0100, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> > > When the memory is insufficient, the allocation of fh fails, which causes
> > > the failure to obtain the dentry fid, and finally causes the dentry encoding
> > > to fail.
> > > Retry is used to avoid the failure of fh allocation caused by temporary
> > > insufficient memory.
> > >
> > > #syz test
> > >
> > > diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
> > > index 2ed6ad641a20..1e027a3cf084 100644
> > > --- a/fs/overlayfs/copy_up.c
> > > +++ b/fs/overlayfs/copy_up.c
> > > @@ -423,15 +423,22 @@ struct ovl_fh *ovl_encode_real_fh(struct ovl_fs *ofs, struct dentry *real,
> > > int fh_type, dwords;
> > > int buflen = MAX_HANDLE_SZ;
> > > uuid_t *uuid = &real->d_sb->s_uuid;
> > > - int err;
> > > + int err, rtt = 0;
> > >
> > > /* Make sure the real fid stays 32bit aligned */
> > > BUILD_BUG_ON(OVL_FH_FID_OFFSET % 4);
> > > BUILD_BUG_ON(MAX_HANDLE_SZ + OVL_FH_FID_OFFSET > 255);
> > >
> > > +retry:
> > > fh = kzalloc(buflen + OVL_FH_FID_OFFSET, GFP_KERNEL);
> > > - if (!fh)
> > > + if (!fh) {
> > > + if (!rtt) {
> > > + cond_resched();
> > > + rtt++;
> > > + goto retry;
> > > + }
> > > return ERR_PTR(-ENOMEM);
> > > + }
> > >
> > > /*
> > > * We encode a non-connectable file handle for non-dir, because we
> > >
> >
> > This endless loop is out of the question and anyway, syzbot reported
> > a WARN_ON in line 448:
> > WARN_ON(fh_type == FILEID_INVALID))
> >
> > How does that have to do with memory allocation failure?
> > What am I missing?
> Look following log, it in https://syzkaller.appspot.com/text?tag=CrashLog&x=178bf640580000:
> [ 64.050342][ T5103] FAULT_INJECTION: forcing a failure.
> [ 64.050342][ T5103] name failslab, interval 1, probability 0, space 0, times 0
> [ 64.055933][ T5103] CPU: 0 UID: 0 PID: 5103 Comm: syz-executor195 Not tainted 6.12.0-rc4-syzkaller-00047-gc2ee9f594da8 #0
> [ 64.060023][ T5103] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> [ 64.063941][ T5103] Call Trace:
> [ 64.065199][ T5103] <TASK>
> [ 64.066296][ T5103] dump_stack_lvl+0x241/0x360
> [ 64.068028][ T5103] ? __pfx_dump_stack_lvl+0x10/0x10
> [ 64.069939][ T5103] ? __pfx__printk+0x10/0x10
> [ 64.071667][ T5103] ? __kmalloc_cache_noprof+0x44/0x2c0
> [ 64.073756][ T5103] ? __pfx___might_resched+0x10/0x10
> [ 64.075720][ T5103] should_fail_ex+0x3b0/0x4e0
> [ 64.077525][ T5103] should_failslab+0xac/0x100
> [ 64.079341][ T5103] ? ovl_encode_real_fh+0xdf/0x410
> [ 64.081295][ T5103] __kmalloc_cache_noprof+0x6c/0x2c0
> [ 64.083282][ T5103] ? dput+0x37/0x2b0
> [ 64.084758][ T5103] ovl_encode_real_fh+0xdf/0x410
> [ 64.086578][ T5103] ? __pfx_ovl_encode_real_fh+0x10/0x10
> [ 64.088687][ T5103] ? _raw_spin_unlock+0x28/0x50
> [ 64.090550][ T5103] ovl_encode_fh+0x388/0xc20
> [ 64.092281][ T5103] exportfs_encode_fh+0x1bd/0x3e0
> [ 64.094122][ T5103] ovl_encode_real_fh+0x129/0x410
> [ 64.095883][ T5103] ? __pfx_ovl_encode_real_fh+0x10/0x10
> [ 64.097852][ T5103] ? bpf_lsm_capable+0x9/0x10
> [ 64.099620][ T5103] ? capable+0x89/0xe0
> [ 64.101064][ T5103] ovl_copy_up_flags+0x1068/0x46f0
I see. it is nested overlayfs, so a memory allocation failure in the lower
overlayfs, causes ovl_encode_fh() to return FILEID_INVALID.
> >
> > Probably this WARN_ON as well as the one in line 446 should be
> > relaxed because it is perfectly possible for fs to return negative or
> > FILEID_INVALID for encoding a file handle even if fs supports encoding
> > file handles.
> >
As I wrote, the correct fix is to relax the WARN_ON from
fh_type == FILEID_INVALID and fh_type < 0 conditions because
those are valid return values from filesystems.
Thanks,
Amir,
