5.4-stable patches

added patches:
	chardev-avoid-potential-use-after-free-in-chrdev_open.patch

diff --git a/queue-5.4/chardev-avoid-potential-use-after-free-in-chrdev_open.patch b/queue-5.4/chardev-avoid-potential-use-after-free-in-chrdev_open.patch
new file mode 100644 (file)
index 0000000..dcd1fc0
--- /dev/null
+++ b/queue-5.4/chardev-avoid-potential-use-after-free-in-chrdev_open.patch
@@ -0,0 +1,96 @@
+From 68faa679b8be1a74e6663c21c3a9d25d32f1c079 Mon Sep 17 00:00:00 2001
+From: Will Deacon <will@kernel.org>
+Date: Thu, 19 Dec 2019 12:02:03 +0000
+Subject: chardev: Avoid potential use-after-free in 'chrdev_open()'
+
+From: Will Deacon <will@kernel.org>
+
+commit 68faa679b8be1a74e6663c21c3a9d25d32f1c079 upstream.
+
+'chrdev_open()' calls 'cdev_get()' to obtain a reference to the
+'struct cdev *' stashed in the 'i_cdev' field of the target inode
+structure. If the pointer is NULL, then it is initialised lazily by
+looking up the kobject in the 'cdev_map' and so the whole procedure is
+protected by the 'cdev_lock' spinlock to serialise initialisation of
+the shared pointer.
+
+Unfortunately, it is possible for the initialising thread to fail *after*
+installing the new pointer, for example if the subsequent '->open()' call
+on the file fails. In this case, 'cdev_put()' is called, the reference
+count on the kobject is dropped and, if nobody else has taken a reference,
+the release function is called which finally clears 'inode->i_cdev' from
+'cdev_purge()' before potentially freeing the object. The problem here
+is that a racing thread can happily take the 'cdev_lock' and see the
+non-NULL pointer in the inode, which can result in a refcount increment
+from zero and a warning:
+
+  |  ------------[ cut here ]------------
+  |  refcount_t: addition on 0; use-after-free.
+  |  WARNING: CPU: 2 PID: 6385 at lib/refcount.c:25 refcount_warn_saturate+0x6d/0xf0
+  |  Modules linked in:
+  |  CPU: 2 PID: 6385 Comm: repro Not tainted 5.5.0-rc2+ #22
+  |  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
+  |  RIP: 0010:refcount_warn_saturate+0x6d/0xf0
+  |  Code: 05 55 9a 15 01 01 e8 9d aa c8 ff 0f 0b c3 80 3d 45 9a 15 01 00 75 ce 48 c7 c7 00 9c 62 b3 c6 08
+  |  RSP: 0018:ffffb524c1b9bc70 EFLAGS: 00010282
+  |  RAX: 0000000000000000 RBX: ffff9e9da1f71390 RCX: 0000000000000000
+  |  RDX: ffff9e9dbbd27618 RSI: ffff9e9dbbd18798 RDI: ffff9e9dbbd18798
+  |  RBP: 0000000000000000 R08: 000000000000095f R09: 0000000000000039
+  |  R10: 0000000000000000 R11: ffffb524c1b9bb20 R12: ffff9e9da1e8c700
+  |  R13: ffffffffb25ee8b0 R14: 0000000000000000 R15: ffff9e9da1e8c700
+  |  FS:  00007f3b87d26700(0000) GS:ffff9e9dbbd00000(0000) knlGS:0000000000000000
+  |  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
+  |  CR2: 00007fc16909c000 CR3: 000000012df9c000 CR4: 00000000000006e0
+  |  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
+  |  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
+  |  Call Trace:
+  |   kobject_get+0x5c/0x60
+  |   cdev_get+0x2b/0x60
+  |   chrdev_open+0x55/0x220
+  |   ? cdev_put.part.3+0x20/0x20
+  |   do_dentry_open+0x13a/0x390
+  |   path_openat+0x2c8/0x1470
+  |   do_filp_open+0x93/0x100
+  |   ? selinux_file_ioctl+0x17f/0x220
+  |   do_sys_open+0x186/0x220
+  |   do_syscall_64+0x48/0x150
+  |   entry_SYSCALL_64_after_hwframe+0x44/0xa9
+  |  RIP: 0033:0x7f3b87efcd0e
+  |  Code: 89 54 24 08 e8 a3 f4 ff ff 8b 74 24 0c 48 8b 3c 24 41 89 c0 44 8b 54 24 08 b8 01 01 00 00 89 f4
+  |  RSP: 002b:00007f3b87d259f0 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
+  |  RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3b87efcd0e
+  |  RDX: 0000000000000000 RSI: 00007f3b87d25a80 RDI: 00000000ffffff9c
+  |  RBP: 00007f3b87d25e90 R08: 0000000000000000 R09: 0000000000000000
+  |  R10: 0000000000000000 R11: 0000000000000293 R12: 00007ffe188f504e
+  |  R13: 00007ffe188f504f R14: 00007f3b87d26700 R15: 0000000000000000
+  |  ---[ end trace 24f53ca58db8180a ]---
+
+Since 'cdev_get()' can already fail to obtain a reference, simply move
+it over to use 'kobject_get_unless_zero()' instead of 'kobject_get()',
+which will cause the racing thread to return -ENXIO if the initialising
+thread fails unexpectedly.
+
+Cc: Hillf Danton <hdanton@sina.com>
+Cc: Andrew Morton <akpm@linux-foundation.org>
+Cc: Al Viro <viro@zeniv.linux.org.uk>
+Reported-by: syzbot+82defefbbd8527e1c2cb@syzkaller.appspotmail.com
+Signed-off-by: Will Deacon <will@kernel.org>
+Cc: stable <stable@vger.kernel.org>
+Link: https://lore.kernel.org/r/20191219120203.32691-1-will@kernel.org
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ fs/char_dev.c |    2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/fs/char_dev.c
++++ b/fs/char_dev.c
+@@ -352,7 +352,7 @@ static struct kobject *cdev_get(struct c
+ 
+       if (owner && !try_module_get(owner))
+               return NULL;
+-      kobj = kobject_get(&p->kobj);
++      kobj = kobject_get_unless_zero(&p->kobj);
+       if (!kobj)
+               module_put(owner);
+       return kobj;