diff options
| author | Davidlohr Bueso <dave@stgolabs.net> | 2026-05-01 12:41:23 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-05-01 13:12:34 -0700 |
| commit | ee9dce44362b2d8132c32964656ab6dff7dfbc6a (patch) | |
| tree | 92cefa9cd46e9e431ed6be5e88a8486d59ab064e /kernel | |
| parent | bb1d73f2cddccf717307e88c24cae619a9a80295 (diff) | |
futex: Drop CLONE_THREAD requirement for private default hash alloc
Currently need_futex_hash_allocate_default() depends on strict pthread
semantics, abusing CLONE_THREAD. This breaks the non-concurrency
assumptions when doing the mm->futex_ref pcpu allocations, leading to
bugs[0] when sharing the mm in other ways; ie:
BUG: KASAN: slab-use-after-free in futex_hash_put
... where the +1 bias can end up on a percpu counter that mm->futex_ref
no longer points at.
Loosen the check to cover any CLONE_VM clone, except vfork(). Excluding
vfork keeps the existing paths untouched (no overhead), and we can't
race in the first place: either the parent is suspended and the child
runs alone, or mm->futex_ref is already allocated from an earlier
CLONE_VM.
Link: https://lore.kernel.org/all/CAL_bE8LsmCQ-FAtYDuwbJhOkt9p2wwYQwAbMh=PifC=VsiBM6A@mail.gmail.com/ [0]
Fixes: d9b05321e21e ("futex: Move futex_hash_free() back to __mmput()")
Reported-by: Yiming Qian <yimingqian591@gmail.com>
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/fork.c | 12 |
1 files changed, 5 insertions, 7 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index f1ad69c6dc2d..5f3fdfdb14c7 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1951,9 +1951,11 @@ static void rv_task_fork(struct task_struct *p) static bool need_futex_hash_allocate_default(u64 clone_flags) { - if ((clone_flags & (CLONE_THREAD | CLONE_VM)) != (CLONE_THREAD | CLONE_VM)) - return false; - return true; + /* + * Allocate a default futex hash for any sibling that will + * share the parent's mm, except vfork. + */ + return (clone_flags & (CLONE_VM | CLONE_VFORK)) == CLONE_VM; } /* @@ -2380,10 +2382,6 @@ __latent_entropy struct task_struct *copy_process( if (retval) goto bad_fork_cancel_cgroup; - /* - * Allocate a default futex hash for the user process once the first - * thread spawns. - */ if (need_futex_hash_allocate_default(clone_flags)) { retval = futex_hash_allocate_default(); if (retval) |