On Thu, Jul 07, 2022 at 10:48:00AM -0700, Yang Shi wrote:
> On Thu, Jul 7, 2022 at 9:57 AM Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> >
> > From: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >
> > syzkaller reports the following issue:
> >
> > BUG: unable to handle page fault for address: ffff888021f7e005
> > PGD 11401067 P4D 11401067 PUD 11402067 PMD 21f7d063 PTE 800fffffde081060
> > Oops: 0002 [#1] PREEMPT SMP KASAN
> > CPU: 0 PID: 3761 Comm: syz-executor281 Not tainted 5.19.0-rc4-syzkaller-00014-g941e3e791269 #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > RIP: 0010:memset_erms+0x9/0x10 arch/x86/lib/memset_64.S:64
> > Code: c1 e9 03 40 0f b6 f6 48 b8 01 01 01 01 01 01 01 01 48 0f af c6 f3 48 ab 89 d1 f3 aa 4c 89 c8 c3 90 49 89 f9 40 88 f0 48 89 d1 <f3> aa 4c 89 c8 c3 90 49 89 fa 40 0f b6 ce 48 b8 01 01 01 01 01 01
> > RSP: 0018:ffffc9000329fa90 EFLAGS: 00010202
> > RAX: 0000000000000000 RBX: 0000000000001000 RCX: 0000000000000ffb
> > RDX: 0000000000000ffb RSI: 0000000000000000 RDI: ffff888021f7e005
> > RBP: ffffea000087df80 R08: 0000000000000001 R09: ffff888021f7e005
> > R10: ffffed10043efdff R11: 0000000000000000 R12: 0000000000000005
> > R13: 0000000000000000 R14: 0000000000001000 R15: 0000000000000ffb
> > FS: 00007fb29d8b2700(0000) GS:ffff8880b9a00000(0000) knlGS:0000000000000000
> > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: ffff888021f7e005 CR3: 0000000026e7b000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> > <TASK>
> > zero_user_segments include/linux/highmem.h:272 [inline]
> > folio_zero_range include/linux/highmem.h:428 [inline]
> > truncate_inode_partial_folio+0x76a/0xdf0 mm/truncate.c:237
> > truncate_inode_pages_range+0x83b/0x1530 mm/truncate.c:381
> > truncate_inode_pages mm/truncate.c:452 [inline]
> > truncate_pagecache+0x63/0x90 mm/truncate.c:753
> > simple_setattr+0xed/0x110 fs/libfs.c:535
> > secretmem_setattr+0xae/0xf0 mm/secretmem.c:170
> > notify_change+0xb8c/0x12b0 fs/attr.c:424
> > do_truncate+0x13c/0x200 fs/open.c:65
> > do_sys_ftruncate+0x536/0x730 fs/open.c:193
> > do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> > entry_SYSCALL_64_after_hwframe+0x46/0xb0
> > RIP: 0033:0x7fb29d900899
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fb29d8b2318 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
> > RAX: ffffffffffffffda RBX: 00007fb29d988408 RCX: 00007fb29d900899
> > RDX: 00007fb29d900899 RSI: 0000000000000005 RDI: 0000000000000003
> > RBP: 00007fb29d988400 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00007fb29d98840c
> > R13: 00007ffca01a23bf R14: 00007fb29d8b2400 R15: 0000000000022000
> > </TASK>
> > Modules linked in:
> > CR2: ffff888021f7e005
> > ---[ end trace 0000000000000000 ]---
> >
> > Eric Biggers suggested that this happens when
> > secretmem_setattr()->simple_setattr() races with secretmem_fault() so
> > that a page that is faulted in by secretmem_fault() (and thus removed
> > from the direct map) is zeroed by inode truncation right afterwards.
> >
> > Since do_truncate() takes inode_lock(), adding inode_lock_shared() to
> > secretmem_fault() prevents the race.
>
> Should invalidate_lock be used to serialize between page fault and truncate?
I would have thought so, given Documentation/filesystems/locking.rst:
"->fault() is called when a previously not present pte is about to be
faulted in. The filesystem must find and return the page associated with
the passed in "pgoff" in the vm_fault structure. If it is possible that
the page may be truncated and/or invalidated, then the filesystem must
lock invalidate_lock, then ensure the page is not already truncated
(invalidate_lock will block subsequent truncate), and then return with
VM_FAULT_LOCKED, and the page locked. The VM will unlock the page."
IIRC page faults aren't supposed to take i_rwsem because the fault could
be in response to someone mmaping a file into memory and then write()ing
to the same file using the mmapped region. The write() takes
inode_lock and faults on the buffer, so the fault cannot take inode_lock
again.
That said... I don't think memfd_secret files /can/ be written to? Hard
to say, since I can't find a manpage describing what that syscall does.
--D
>
> >
> > Reported-by: syzbot+9bd2b7adbd34b30b87e4@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Suggested-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> > Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> > ---
> >
> > v2: use inode_lock_shared() rather than add a new rw_sem to secretmem
> >
> > Axel, I didn't add your Reviewed-by because v2 is quite different.
> >
> > mm/secretmem.c | 21 ++++++++++++++++-----
> > 1 file changed, 16 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/secretmem.c b/mm/secretmem.c
> > index 206ed6b40c1d..a4fabf705e4f 100644
> > --- a/mm/secretmem.c
> > +++ b/mm/secretmem.c
> > @@ -55,22 +55,28 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> > gfp_t gfp = vmf->gfp_mask;
> > unsigned long addr;
> > struct page *page;
> > + vm_fault_t ret;
> > int err;
> >
> > if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
> > return vmf_error(-EINVAL);
> >
> > + inode_lock_shared(inode);
> > +
> > retry:
> > page = find_lock_page(mapping, offset);
> > if (!page) {
> > page = alloc_page(gfp | __GFP_ZERO);
> > - if (!page)
> > - return VM_FAULT_OOM;
> > + if (!page) {
> > + ret = VM_FAULT_OOM;
> > + goto out;
> > + }
> >
> > err = set_direct_map_invalid_noflush(page);
> > if (err) {
> > put_page(page);
> > - return vmf_error(err);
> > + ret = vmf_error(err);
> > + goto out;
> > }
> >
> > __SetPageUptodate(page);
> > @@ -86,7 +92,8 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> > if (err == -EEXIST)
> > goto retry;
> >
> > - return vmf_error(err);
> > + ret = vmf_error(err);
> > + goto out;
> > }
> >
> > addr = (unsigned long)page_address(page);
> > @@ -94,7 +101,11 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf)
> > }
> >
> > vmf->page = page;
> > - return VM_FAULT_LOCKED;
> > + ret = VM_FAULT_LOCKED;
> > +
> > +out:
> > + inode_unlock_shared(inode);
> > + return ret;
> > }
> >
> > static const struct vm_operations_struct secretmem_vm_ops = {
> >
> > base-commit: 03c765b0e3b4cb5063276b086c76f7a612856a9a
> > --
> > 2.34.1
> >
> >
