/[packages]/updates/7/kernel/current/SOURCES/chardev-avoid-potential-use-after-free-in-chrdev_open.patch
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Contents of /updates/7/kernel/current/SOURCES/chardev-avoid-potential-use-after-free-in-chrdev_open.patch

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Revision 1477830 - (show annotations) (download)
Mon Jan 13 19:51:01 2020 UTC (4 years, 2 months ago) by tmb
File size: 4519 byte(s)
- update to 5.4.11
- add current -stable queue


1 From 68faa679b8be1a74e6663c21c3a9d25d32f1c079 Mon Sep 17 00:00:00 2001
2 From: Will Deacon <will@kernel.org>
3 Date: Thu, 19 Dec 2019 12:02:03 +0000
4 Subject: chardev: Avoid potential use-after-free in 'chrdev_open()'
5
6 From: Will Deacon <will@kernel.org>
7
8 commit 68faa679b8be1a74e6663c21c3a9d25d32f1c079 upstream.
9
10 'chrdev_open()' calls 'cdev_get()' to obtain a reference to the
11 'struct cdev *' stashed in the 'i_cdev' field of the target inode
12 structure. If the pointer is NULL, then it is initialised lazily by
13 looking up the kobject in the 'cdev_map' and so the whole procedure is
14 protected by the 'cdev_lock' spinlock to serialise initialisation of
15 the shared pointer.
16
17 Unfortunately, it is possible for the initialising thread to fail *after*
18 installing the new pointer, for example if the subsequent '->open()' call
19 on the file fails. In this case, 'cdev_put()' is called, the reference
20 count on the kobject is dropped and, if nobody else has taken a reference,
21 the release function is called which finally clears 'inode->i_cdev' from
22 'cdev_purge()' before potentially freeing the object. The problem here
23 is that a racing thread can happily take the 'cdev_lock' and see the
24 non-NULL pointer in the inode, which can result in a refcount increment
25 from zero and a warning:
26
27 | ------------[ cut here ]------------
28 | refcount_t: addition on 0; use-after-free.
29 | WARNING: CPU: 2 PID: 6385 at lib/refcount.c:25 refcount_warn_saturate+0x6d/0xf0
30 | Modules linked in:
31 | CPU: 2 PID: 6385 Comm: repro Not tainted 5.5.0-rc2+ #22
32 | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
33 | RIP: 0010:refcount_warn_saturate+0x6d/0xf0
34 | 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
35 | RSP: 0018:ffffb524c1b9bc70 EFLAGS: 00010282
36 | RAX: 0000000000000000 RBX: ffff9e9da1f71390 RCX: 0000000000000000
37 | RDX: ffff9e9dbbd27618 RSI: ffff9e9dbbd18798 RDI: ffff9e9dbbd18798
38 | RBP: 0000000000000000 R08: 000000000000095f R09: 0000000000000039
39 | R10: 0000000000000000 R11: ffffb524c1b9bb20 R12: ffff9e9da1e8c700
40 | R13: ffffffffb25ee8b0 R14: 0000000000000000 R15: ffff9e9da1e8c700
41 | FS: 00007f3b87d26700(0000) GS:ffff9e9dbbd00000(0000) knlGS:0000000000000000
42 | CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
43 | CR2: 00007fc16909c000 CR3: 000000012df9c000 CR4: 00000000000006e0
44 | DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
45 | DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
46 | Call Trace:
47 | kobject_get+0x5c/0x60
48 | cdev_get+0x2b/0x60
49 | chrdev_open+0x55/0x220
50 | ? cdev_put.part.3+0x20/0x20
51 | do_dentry_open+0x13a/0x390
52 | path_openat+0x2c8/0x1470
53 | do_filp_open+0x93/0x100
54 | ? selinux_file_ioctl+0x17f/0x220
55 | do_sys_open+0x186/0x220
56 | do_syscall_64+0x48/0x150
57 | entry_SYSCALL_64_after_hwframe+0x44/0xa9
58 | RIP: 0033:0x7f3b87efcd0e
59 | 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
60 | RSP: 002b:00007f3b87d259f0 EFLAGS: 00000293 ORIG_RAX: 0000000000000101
61 | RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3b87efcd0e
62 | RDX: 0000000000000000 RSI: 00007f3b87d25a80 RDI: 00000000ffffff9c
63 | RBP: 00007f3b87d25e90 R08: 0000000000000000 R09: 0000000000000000
64 | R10: 0000000000000000 R11: 0000000000000293 R12: 00007ffe188f504e
65 | R13: 00007ffe188f504f R14: 00007f3b87d26700 R15: 0000000000000000
66 | ---[ end trace 24f53ca58db8180a ]---
67
68 Since 'cdev_get()' can already fail to obtain a reference, simply move
69 it over to use 'kobject_get_unless_zero()' instead of 'kobject_get()',
70 which will cause the racing thread to return -ENXIO if the initialising
71 thread fails unexpectedly.
72
73 Cc: Hillf Danton <hdanton@sina.com>
74 Cc: Andrew Morton <akpm@linux-foundation.org>
75 Cc: Al Viro <viro@zeniv.linux.org.uk>
76 Reported-by: syzbot+82defefbbd8527e1c2cb@syzkaller.appspotmail.com
77 Signed-off-by: Will Deacon <will@kernel.org>
78 Cc: stable <stable@vger.kernel.org>
79 Link: https://lore.kernel.org/r/20191219120203.32691-1-will@kernel.org
80 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
81
82 ---
83 fs/char_dev.c | 2 +-
84 1 file changed, 1 insertion(+), 1 deletion(-)
85
86 --- a/fs/char_dev.c
87 +++ b/fs/char_dev.c
88 @@ -352,7 +352,7 @@ static struct kobject *cdev_get(struct c
89
90 if (owner && !try_module_get(owner))
91 return NULL;
92 - kobj = kobject_get(&p->kobj);
93 + kobj = kobject_get_unless_zero(&p->kobj);
94 if (!kobj)
95 module_put(owner);
96 return kobj;

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