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arc=pass ("microsoft.com:s=arcselector9901:i=1") ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1660071752; a=rsa-sha256; cv=pass; b=Du3QoO+X1+vHEymCQBS6ed8Pw0VFfC6+bbg6efAHZVaacn9nw0vS/gaGLIAXme0FDoL0Vw wqyqTrc1RikSkVaOmKA4HRo+TDam8BmnH7f3pwZmtyCnFe01ylupHH3pmg2czop9Sfy1Ka d1/xHQ3gncyjvBm1sQHNRFE1w+fXTAE= X-Rspamd-Queue-Id: E659540024 X-Rspamd-Server: rspam03 X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=bymspl0R; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=Gdj27CVD; dmarc=pass (policy=none) header.from=oracle.com; spf=pass (imf04.hostedemail.com: domain of liam.howlett@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=liam.howlett@oracle.com; arc=pass ("microsoft.com:s=arcselector9901:i=1") X-Stat-Signature: 53azyb5j4entbdz73c9cjreww1kq6azh X-HE-Tag: 1660071751-225493 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: * Carlos Llamas [220809 14:49]: > On Tue, Aug 09, 2022 at 04:06:31PM +0000, Liam Howlett wrote: > > Take the mmap_read_lock() when using the VMA in > > binder_alloc_print_pages() and when checking for a VMA in > > binder_alloc_new_buf_locked(). > >=20 > > It is worth noting binder_alloc_new_buf_locked() drops the VMA read loc= k > > after it verifies a VMA exists, but may be taken again deeper in the > > call stack, if necessary. > >=20 > > Reported-by: Ondrej Mosnacek > > Reported-by: syzbot+a7b60a176ec13cafb793@syzkaller.appspotmail.com > > Fixes: a43cfc87caaf (android: binder: stop saving a pointer to the VMA) > > Signed-off-by: Liam R. Howlett > > --- > > drivers/android/binder_alloc.c | 29 +++++++++++++++++++---------- > > 1 file changed, 19 insertions(+), 10 deletions(-) > >=20 > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_al= loc.c > > index f555eebceef6..c23cad7fe313 100644 > > --- a/drivers/android/binder_alloc.c > > +++ b/drivers/android/binder_alloc.c > > @@ -395,12 +395,15 @@ static struct binder_buffer *binder_alloc_new_buf= _locked( > > size_t size, data_offsets_size; > > int ret; > > =20 > > + mmap_read_lock(alloc->vma_vm_mm); > > if (!binder_alloc_get_vma(alloc)) { > > + mmap_read_unlock(alloc->vma_vm_mm); > > binder_alloc_debug(BINDER_DEBUG_USER_ERROR, > > "%d: binder_alloc_buf, no vma\n", > > alloc->pid); > > return ERR_PTR(-ESRCH); > > } > > + mmap_read_unlock(alloc->vma_vm_mm); > > =20 > > data_offsets_size =3D ALIGN(data_size, sizeof(void *)) + > > ALIGN(offsets_size, sizeof(void *)); > > @@ -922,17 +925,23 @@ void binder_alloc_print_pages(struct seq_file *m, > > * Make sure the binder_alloc is fully initialized, otherwise we migh= t > > * read inconsistent state. > > */ > > - if (binder_alloc_get_vma(alloc) !=3D NULL) { > > - for (i =3D 0; i < alloc->buffer_size / PAGE_SIZE; i++) { > > - page =3D &alloc->pages[i]; > > - if (!page->page_ptr) > > - free++; > > - else if (list_empty(&page->lru)) > > - active++; > > - else > > - lru++; > > - } > > + > > + mmap_read_lock(alloc->vma_vm_mm); > > + if (binder_alloc_get_vma(alloc) =3D=3D NULL) > > + goto uninitialized; > > + > > + for (i =3D 0; i < alloc->buffer_size / PAGE_SIZE; i++) { >=20 > do we need to hold on to the lock while we loop through the pages here? I think we do? Holding this lock will ensure the pages don't go away, I believe (looking at mm/rmap.c comments on locking at the top)? In any case, this function is called from print_binder_proc_stats() which looks to be a debugfs/debugging call so I thought safer would be better than faster and with a potential race. >=20 > > + page =3D &alloc->pages[i]; > > + if (!page->page_ptr) > > + free++; > > + else if (list_empty(&page->lru)) > > + active++; > > + else > > + lru++; > > } > > + > > +uninitialized: > > + mmap_read_unlock(alloc->vma_vm_mm); > > mutex_unlock(&alloc->mutex); > > seq_printf(m, " pages: %d:%d:%d\n", active, lru, free); > > seq_printf(m, " pages high watermark: %zu\n", alloc->pages_high); > > --=20 > > 2.35.1=