From: Jiri Olsa <olsajiri@gmail.com>
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
Fixes: 1cc33161a83d ("uprobes: Support SDT markers having reference count (semaphore)")
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
v2 changes:
- adding proper Fixes tag and acks
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);
/* try collapse pmd for compound page */
if (ret > 0)
--
2.49.0