Messages in this thread | | | Date | Fri, 4 Aug 2023 15:20:45 +0200 | From | Christian Brauner <> | Subject | Re: [syzbot] [fs?] KASAN: slab-use-after-free Read in test_bdev_super_fc |
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On Fri, Aug 04, 2023 at 12:14:08PM +0200, Christoph Hellwig wrote: > FYI, I can reproduce this trivially locally, but even after spending a > significant time with the trace I'm still puzzled at what is going > on. I've started trying to make sense of the lockdep report about > returning to userspace with s_umount held, originall locked in > get_tree_bdev and am still missing how it could happen.
So in the old scheme:
s = alloc_super() -> down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
and assume you're not finding an old one immediately afterwards you'd
-> spin_lock(&sb_lock)
static int set_bdev_super(struct super_block *s, void *data) { s->s_bdev = data; s->s_dev = s->s_bdev->bd_dev; s->s_bdi = bdi_get(s->s_bdev->bd_disk->bdi);
if (bdev_stable_writes(s->s_bdev)) s->s_iflags |= SB_I_STABLE_WRITES; return 0; }
-> spin_unlock(&sb_lock)
in the new scheme you're doing:
s = alloc_super() -> down_write_nested(&s->s_umount, SINGLE_DEPTH_NESTING);
and assume you're not finding an old one immediately afterwards you'd
up_write(&s->s_umount);
error = setup_bdev_super(s, fc->sb_flags, fc); -> spin_lock(&sb_lock); sb->s_bdev = bdev; sb->s_bdi = bdi_get(bdev->bd_disk->bdi); if (bdev_stable_writes(bdev)) sb->s_iflags |= SB_I_STABLE_WRITES; -> spin_unlock(&sb_lock);
down_write(&s->s_umount);
Which looks like the lock ordering here is changed?
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