On Wed, May 9, 2018 at 6:57 PM 'Todd Kjos' via syzkaller-bugs
<syzkaller-bugs@xxxxxxxxxxxxxxxx> wrote:
>
> +Joel Fernandes
>
> On Wed, May 9, 2018 at 12:55 AM Eric Biggers <ebiggers3@xxxxxxxxx> wrote:
>>
>> [+ashmem maintainers]
>>
>> On Sun, Apr 29, 2018 at 10:00:03AM -0700, syzbot wrote:
>> > Hello,
>> >
>> > syzbot hit the following crash on upstream commit
>> > cdface5209349930ae1b51338763c8e029971b97 (Sun Apr 29 03:07:21 2018 +0000)
>> > Merge tag 'for_linus_stable' of
>> > git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4
>> > syzbot dashboard link:
>> > https://syzkaller.appspot.com/bug?extid=148c2885d71194f18d28
>> >
>> > C reproducer: https://syzkaller.appspot.com/x/repro.c?id=5054004375584768
>> > syzkaller reproducer:
>> > https://syzkaller.appspot.com/x/repro.syz?id=6438048191479808
>> > Raw console output:
>> > https://syzkaller.appspot.com/x/log.txt?id=5404215203594240
>> > Kernel config:
>> > https://syzkaller.appspot.com/x/.config?id=7043958930931867332
>> > compiler: gcc (GCC) 8.0.1 20180413 (experimental)
Let's test Tetsuo's patch
#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master
>> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> > Reported-by: syzbot+148c2885d71194f18d28@xxxxxxxxxxxxxxxxxxxxxxxxx
>> > It will help syzbot understand when the bug is fixed. See footer for
>> > details.
>> > If you forward the report, please keep this part and the footer.
>> >
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> > random: sshd: uninitialized urandom read (32 bytes read)
>> >
>> > ======================================================
>> > WARNING: possible circular locking dependency detected
>> > 4.17.0-rc2+ #23 Not tainted
>> > ------------------------------------------------------
>> > syz-executor715/4492 is trying to acquire lock:
>> > (ptrval) (sb_writers#6){.+.+}, at: file_start_write
>> > include/linux/fs.h:2718 [inline]
>> > (ptrval) (sb_writers#6){.+.+}, at: vfs_fallocate+0x5be/0x8d0
>> > fs/open.c:318
>> >
>> > but task is already holding lock:
>> > (ptrval) (ashmem_mutex){+.+.}, at: ashmem_shrink_scan+0xac/0x560
>> > drivers/staging/android/ashmem.c:440
>> >
>> > which lock already depends on the new lock.
>> >
>> >
>> > the existing dependency chain (in reverse order) is:
>> >
>> > -> #3 (ashmem_mutex){+.+.}:
>> > __mutex_lock_common kernel/locking/mutex.c:756 [inline]
>> > __mutex_lock+0x16d/0x17f0 kernel/locking/mutex.c:893
>> > mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
>> > ashmem_mmap+0x53/0x460 drivers/staging/android/ashmem.c:361
>> > call_mmap include/linux/fs.h:1789 [inline]
>> > mmap_region+0xd13/0x1820 mm/mmap.c:1723
>> > do_mmap+0xc79/0x11d0 mm/mmap.c:1494
>> > do_mmap_pgoff include/linux/mm.h:2237 [inline]
>> > vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:357
>> > ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
>> > __do_sys_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
>> > __se_sys_mmap arch/x86/kernel/sys_x86_64.c:91 [inline]
>> > __x64_sys_mmap+0xe9/0x1b0 arch/x86/kernel/sys_x86_64.c:91
>> > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #2 (&mm->mmap_sem){++++}:
>> > __might_fault+0x155/0x1e0 mm/memory.c:4555
>> > _copy_to_user+0x30/0x110 lib/usercopy.c:25
>> > copy_to_user include/linux/uaccess.h:155 [inline]
>> > filldir+0x1ea/0x3a0 fs/readdir.c:196
>> > dir_emit_dot include/linux/fs.h:3378 [inline]
>> > dir_emit_dots include/linux/fs.h:3389 [inline]
>> > dcache_readdir+0x13a/0x620 fs/libfs.c:192
>> > iterate_dir+0x4b0/0x5d0 fs/readdir.c:51
>> > __do_sys_getdents fs/readdir.c:231 [inline]
>> > __se_sys_getdents fs/readdir.c:212 [inline]
>> > __x64_sys_getdents+0x293/0x4e0 fs/readdir.c:212
>> > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #1 (&sb->s_type->i_mutex_key#11){++++}:
>> > down_write+0x87/0x120 kernel/locking/rwsem.c:70
>> > inode_lock include/linux/fs.h:713 [inline]
>> > do_last fs/namei.c:3274 [inline]
>> > path_openat+0x123b/0x4e20 fs/namei.c:3501
>> > do_filp_open+0x249/0x350 fs/namei.c:3535
>> > do_sys_open+0x56f/0x740 fs/open.c:1093
>> > __do_sys_open fs/open.c:1111 [inline]
>> > __se_sys_open fs/open.c:1106 [inline]
>> > __x64_sys_open+0x7e/0xc0 fs/open.c:1106
>> > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > -> #0 (sb_writers#6){.+.+}:
>> > lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>> > percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36
>> > [inline]
>> > percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>> > __sb_start_write+0x1e9/0x300 fs/super.c:1385
>> > file_start_write include/linux/fs.h:2718 [inline]
>> > vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>> > ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>> > ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>> > vfs_ioctl fs/ioctl.c:46 [inline]
>> > file_ioctl fs/ioctl.c:500 [inline]
>> > do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>> > ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>> > __do_sys_ioctl fs/ioctl.c:708 [inline]
>> > __se_sys_ioctl fs/ioctl.c:706 [inline]
>> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>> > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> >
>> > other info that might help us debug this:
>> >
>> > Chain exists of:
>> > sb_writers#6 --> &mm->mmap_sem --> ashmem_mutex
>> >
>> > Possible unsafe locking scenario:
>> >
>> > CPU0 CPU1
>> > ---- ----
>> > lock(ashmem_mutex);
>> > lock(&mm->mmap_sem);
>> > lock(ashmem_mutex);
>> > lock(sb_writers#6);
>> >
>> > *** DEADLOCK ***
>> >
>> > 1 lock held by syz-executor715/4492:
>> > #0: (ptrval) (ashmem_mutex){+.+.}, at:
>> > ashmem_shrink_scan+0xac/0x560 drivers/staging/android/ashmem.c:440
>> >
>> > stack backtrace:
>> > CPU: 1 PID: 4492 Comm: syz-executor715 Not tainted 4.17.0-rc2+ #23
>> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
>> > Google 01/01/2011
>> > Call Trace:
>> > __dump_stack lib/dump_stack.c:77 [inline]
>> > dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>> > print_circular_bug.isra.36.cold.54+0x1bd/0x27d
>> > kernel/locking/lockdep.c:1223
>> > check_prev_add kernel/locking/lockdep.c:1863 [inline]
>> > check_prevs_add kernel/locking/lockdep.c:1976 [inline]
>> > validate_chain kernel/locking/lockdep.c:2417 [inline]
>> > __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
>> > lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
>> > percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
>> > percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
>> > __sb_start_write+0x1e9/0x300 fs/super.c:1385
>> > file_start_write include/linux/fs.h:2718 [inline]
>> > vfs_fallocate+0x5be/0x8d0 fs/open.c:318
>> > ashmem_shrink_scan+0x1f1/0x560 drivers/staging/android/ashmem.c:447
>> > ashmem_ioctl+0x3bf/0x13a0 drivers/staging/android/ashmem.c:789
>> > vfs_ioctl fs/ioctl.c:46 [inline]
>> > file_ioctl fs/ioctl.c:500 [inline]
>> > do_vfs_ioctl+0x1cf/0x16a0 fs/ioctl.c:684
>> > ksys_ioctl+0xa9/0xd0 fs/ioctl.c:701
>> > __do_sys_ioctl fs/ioctl.c:708 [inline]
>> > __se_sys_ioctl fs/ioctl.c:706 [inline]
>> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:706
>> > do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
>> > RIP: 0033:0x440179
>> > RSP: 002b:00007ffc165d4a28 EFLAGS: 00000217 ORIG_RAX: 0000000000000010
>> > RAX: ffffffffffffffda RBX: 6873612f7665642f RCX: 0000000000440179
>> > RDX: 0000000000000000 RSI: 000000000000770a RDI: 0000000000000004
>> > RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
>> > R10: 0000000000000004 R11: 0000000000000217 R12: 00000000004016a0
>> > R13: 0000000000401730 R14: 0000000000000000 R15: 0000000000000000
>> > random: crng init done
>> >
>> >
>> > ---
>> > This bug is generated by a dumb bot. It may contain errors.
>> > See https://goo.gl/tpsmEJ for details.
>> > Direct all questions to syzkaller@xxxxxxxxxxxxxxxx.
>> >
>> > syzbot will keep track of this bug report.
>> > If you forgot to add the Reported-by tag, once the fix for this bug is
>> > merged
>> > into any tree, please reply to this email with:
>> > #syz fix: exact-commit-title
>> > If you want to test a patch for this bug, please reply with:
>> > #syz test: git://repo/address.git branch
>> > and provide the patch inline or as an attachment.
>> > To mark this as a duplicate of another syzbot report, please reply with:
>> > #syz dup: exact-subject-of-another-report
>> > If it's a one-off invalid bug report, please reply with:
>> > #syz invalid
>> > Note: if the crash happens again, it will cause creation of a new bug
>> > report.
>> > Note: all commands must start from beginning of the line in the email body.
>>
>> Looks like yet another locking bug in ashmem. ashmem_mutex normally ranks below
>> mmap_sem, but ashmem_shrink_scan() inverts that order, via the
>> file_start_write() in vfs_fallocate().
>>
>> - Eric
diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 90a8a9f1ac7d..1a890c43a10a 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -75,6 +75,17 @@ struct ashmem_range {
/* LRU list of unpinned pages, protected by ashmem_mutex */
static LIST_HEAD(ashmem_lru_list);
+static struct workqueue_struct *ashmem_wq;
+static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0);
+static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait);
+
+struct ashmem_shrink_work {
+ struct work_struct work;
+ struct file *file;
+ loff_t start;
+ loff_t end;
+};
+
/*
* long lru_count - The count of pages on our LRU list.
*
@@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter)
int ret = 0;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
/* If size is not set, or set to 0, always return EOF. */
if (asma->size == 0)
@@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
int ret = 0;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
/* user needs to SET_SIZE before mapping */
if (!asma->size) {
@@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma)
return ret;
}
+static void ashmem_shrink_worker(struct work_struct *work)
+{
+ struct ashmem_shrink_work *w = container_of(work, typeof(*w), work);
+
+ w->file->f_op->fallocate(w->file,
+ FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+ w->start, w->end - w->start);
+ fput(w->file);
+ kfree(w);
+ if (atomic_dec_and_test(&ashmem_shrink_inflight))
+ wake_up_all(&ashmem_shrink_wait);
+}
+
/*
* ashmem_shrink - our cache shrinker, called from mm/vmscan.c
*
@@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
return -1;
list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
- loff_t start = range->pgstart * PAGE_SIZE;
- loff_t end = (range->pgend + 1) * PAGE_SIZE;
+ struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC);
+
+ if (!w)
+ break;
+ INIT_WORK(&w->work, ashmem_shrink_worker);
+ w->file = range->asma->file;
+ get_file(w->file);
+ w->start = range->pgstart * PAGE_SIZE;
+ w->end = (range->pgend + 1) * PAGE_SIZE;
+ atomic_inc(&ashmem_shrink_inflight);
+ queue_work(ashmem_wq, &w->work);
- range->asma->file->f_op->fallocate(range->asma->file,
- FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
- start, end - start);
range->purged = ASHMEM_WAS_PURGED;
lru_del(range);
@@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
return -EFAULT;
mutex_lock(&ashmem_mutex);
+ wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight));
if (!asma->file)
goto out_unlock;
@@ -883,8 +916,15 @@ static int __init ashmem_init(void)
goto out_free2;
}
+ ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0);
+ if (!ashmem_wq) {
+ pr_err("failed to create workqueue\n");
+ goto out_demisc;
+ }
+
ret = register_shrinker(&ashmem_shrinker);
if (ret) {
+ destroy_workqueue(ashmem_wq);
pr_err("failed to register shrinker!\n");
goto out_demisc;
}
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