On Tue, May 13, 2025 at 03:17:46PM +0200, David Hildenbrand wrote: > On 13.05.25 15:16, David Hildenbrand wrote: > > On 13.05.25 14:21, Jiri Olsa wrote: > > > From: Jiri Olsa <[email protected]> > > > > > > > Thanks for debugging. > > > > > There's error path that could lead to inactive uprobe: > > > > > > 1) uprobe_register succeeds - updates instruction to int3 and > > > changes ref_ctr from 0 to 1 > > > 2) uprobe_unregister fails - int3 stays in place, but ref_ctr > > > is changed to 0 (it's not restored to 1 in the fail path) > > > uprobe is leaked > > > 3) another uprobe_register comes and re-uses the leaked uprobe > > > and succeds - but int3 is already in place, so ref_ctr update > > > is skipped and it stays 0 - uprobe CAN NOT be triggered now > > > 4) uprobe_unregister fails because ref_ctr value is unexpected > > > > > > Fixing this by reverting the updated ref_ctr value back to 1 in step 2), > > > which is the case when uprobe_unregister fails (int3 stays in place), > > > but we have already updated refctr. > > > > > > The new scenario will go as follows: > > > > > > 1) uprobe_register succeeds - updates instruction to int3 and > > > changes ref_ctr from 0 to 1 > > > 2) uprobe_unregister fails - int3 stays in place and ref_ctr > > > is reverted to 1.. uprobe is leaked > > > 3) another uprobe_register comes and re-uses the leaked uprobe > > > and succeds - but int3 is already in place, so ref_ctr update > > > is skipped and it stays 1 - uprobe CAN be triggered now > > > 4) uprobe_unregister succeeds > > > > > > Suggested-by: Oleg Nesterov <[email protected]> > > > > If it's in mm-stable, we should have > > > > Fixes: ...
ok > > > > here > > > > > Signed-off-by: Jiri Olsa <[email protected]> > > > --- > > > Please note it's based on mm-stable branch, because it has the > > > latest uprobe_write_opcode rewrite changes. > > > > > > kernel/events/uprobes.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > > index 4c965ba77f9f..84ee7b590861 100644 > > > --- a/kernel/events/uprobes.c > > > +++ b/kernel/events/uprobes.c > > > @@ -581,8 +581,8 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, > > > struct vm_area_struct *vma, > > > out: > > > /* Revert back reference counter if instruction update failed. > > > */ > > > - if (ret < 0 && is_register && ref_ctr_updated) > > > - update_ref_ctr(uprobe, mm, -1); > > > + if (ret < 0 && ref_ctr_updated) > > > + update_ref_ctr(uprobe, mm, is_register ? -1 : 1); > > > > > > Hm, but my patch essentially did here > > > > /* Revert back reference counter if instruction update failed. */ > > - if (ret && is_register && ref_ctr_updated) > > + if (ret < 0 && is_register && ref_ctr_updated) > > update_ref_ctr(uprobe, mm, -1); > > > > So how come this wasn't a problem before? > > Oh, or was this a problem before? Then we should find the corresponding > commit that needs fixing. yes, I think it was a problem before, introduced early on by: 1cc33161a83d uprobes: Support SDT markers having reference count (semaphore) it seems the scenario described in changelog will hit the same issue even without your patch, I'll re-run the test to be sure thanks, jirka
