From: Xiongfeng Wang wangxiongfeng2@huawei.com

hulk inclusion category: bugfix bugzilla: 175146 CVE: NA

------------------------------------

Syzkaller caught the following BUG_ON:

------------[ cut here ]------------ kernel BUG at fs/userfaultfd.c:909! Internal error: Oops - BUG: 0 [#1] SMP Dumping ftrace buffer: (ftrace buffer empty) Modules linked in: Process syz-executor.2 (pid: 1994, stack limit = 0x0000000048da525b) CPU: 0 PID: 1994 Comm: syz-executor.2 Not tainted 4.19.90+ #6 Hardware name: linux,dummy-virt (DT) pstate: 80000005 (Nzcv daif -PAN -UAO) pc : userfaultfd_release+0x4f0/0x6a0 fs/userfaultfd.c:908 lr : userfaultfd_release+0x4f0/0x6a0 fs/userfaultfd.c:908 sp : ffff80017d247c80 x29: ffff80017d247c90 x28: ffff80019b25f720 x27: 2000000000100077 x26: ffff80017c28fe40 x25: ffff80019b25f770 x24: ffff80019b25f7e0 x23: ffff80019b25e378 x22: 1ffff0002fa48fa6 x21: ffff80017f103200 x20: dfff200000000000 x19: ffff80017c28fe40 x18: 0000000000000000 x17: ffffffff00000001 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : 1ffff0002fa48fa6 x8 : ffff10002fa48fa6 x7 : ffff20000add39f0 x6 : 00000000f2000000 x5 : 0000000000000000 x4 : ffff10002fa48f76 x3 : ffff200008000000 x2 : ffff20000a61d000 x1 : ffff800160aa9000 x0 : 0000000000000000 Call trace: userfaultfd_release+0x4f0/0x6a0 fs/userfaultfd.c:908 __fput+0x20c/0x688 fs/file_table.c:278 ____fput+0x24/0x30 fs/file_table.c:309 task_work_run+0x13c/0x2f8 kernel/task_work.c:135 tracehook_notify_resume include/linux/tracehook.h:193 [inline] do_notify_resume+0x380/0x628 arch/arm64/kernel/signal.c:728 work_pending+0x8/0x10 Code: 97ecb0e4 d4210000 17ffffc7 97ecb0e1 (d4210000) ---[ end trace de790a3f637d9e60 ]---

In userfaultfd_release(), we check if 'vm_userfaultfd_ctx' and 'vm_flags&(VM_UFFD_MISSING|VM_UFFD_WP)' are not zero at the same time. If not, it is bug. But we lack checking for VM_USWAP flag. So add it to avoid the false BUG_ON(). This patch also fix several other issues.

Fixes: c3e6287f88f5 ("userswap: support userswap via userfaultfd") Signed-off-by: Xiongfeng Wang wangxiongfeng2@huawei.com Reviewed-by: Kefeng Wang wangkefeng.wang@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/userfaultfd.c | 12 +++++++++--- mm/memory.c | 1 - 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index 0d19adb40dc2e..978fc69c4dbb1 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -884,7 +884,7 @@ static int userfaultfd_release(struct inode *inode, struct file *file) struct vm_area_struct *vma, *prev; /* len == 0 means wake all */ struct userfaultfd_wake_range range = { .len = 0, }; - unsigned long new_flags; + unsigned long new_flags, userfault_flags; bool still_valid;

WRITE_ONCE(ctx->released, true); @@ -904,14 +904,18 @@ static int userfaultfd_release(struct inode *inode, struct file *file) still_valid = mmget_still_valid(mm); prev = NULL; for (vma = mm->mmap; vma; vma = vma->vm_next) { + userfault_flags = VM_UFFD_MISSING | VM_UFFD_WP; +#ifdef CONFIG_USERSWAP + userfault_flags |= VM_USWAP; +#endif cond_resched(); BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ - !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); + !!(vma->vm_flags & userfault_flags)); if (vma->vm_userfaultfd_ctx.ctx != ctx) { prev = vma; continue; } - new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); + new_flags = vma->vm_flags & ~userfault_flags; if (still_valid) { prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, new_flags, vma->anon_vma, @@ -1333,6 +1337,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx, */ if (uffdio_register.mode & UFFDIO_REGISTER_MODE_USWAP) { uffdio_register.mode &= ~UFFDIO_REGISTER_MODE_USWAP; + if (!uffdio_register.mode) + goto out; vm_flags |= VM_USWAP; end = uffdio_register.range.start + uffdio_register.range.len - 1; vma = find_vma(mm, uffdio_register.range.start); diff --git a/mm/memory.c b/mm/memory.c index 05987251c1c75..d9f4e7dd17a67 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2909,7 +2909,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) vmf->address, vma->vm_flags); goto skip_uswap; } - BUG_ON(!(vma->vm_flags & VM_UFFD_MISSING)); ret = handle_userfault(vmf, VM_UFFD_MISSING | VM_USWAP); return ret; }