Subject: CVE-2024-46771: can: bcm: Remove proc entry when dev is unregistered.

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

can: bcm: Remove proc entry when dev is unregistered.

syzkaller reported a warning in bcm_connect() below. [0]

The repro calls connect() to vxcan1, removes vxcan1, and calls
connect() with ifindex == 0.

Calling connect() for a BCM socket allocates a proc entry.
Then, bcm_sk(sk)->bound is set to 1 to prevent further connect().

However, removing the bound device resets bcm_sk(sk)->bound to 0
in bcm_notify().

The 2nd connect() tries to allocate a proc entry with the same
name and sets NULL to bcm_sk(sk)->bcm_proc_read, leaking the
original proc entry.

Since the proc entry is available only for connect()ed sockets,
let's clean up the entry when the bound netdev is unregistered.

[0]:
proc_dir_entry 'can-bcm/2456' already registered
WARNING: CPU: 1 PID: 394 at fs/proc/generic.c:376 proc_register+0x645/0x8f0 fs/proc/generic.c:375
Modules linked in:
CPU: 1 PID: 394 Comm: syz-executor403 Not tainted 6.10.0-rc7-g852e42cc2dd4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:proc_register+0x645/0x8f0 fs/proc/generic.c:375
Code: 00 00 00 00 00 48 85 ed 0f 85 97 02 00 00 4d 85 f6 0f 85 9f 02 00 00 48 c7 c7 9b cb cf 87 48 89 de 4c 89 fa e8 1c 6f eb fe 90 <0f> 0b 90 90 48 c7 c7 98 37 99 89 e8 cb 7e 22 05 bb 00 00 00 10 48
RSP: 0018:ffa0000000cd7c30 EFLAGS: 00010246
RAX: 9e129be1950f0200 RBX: ff1100011b51582c RCX: ff1100011857cd80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000002
RBP: 0000000000000000 R08: ffd400000000000f R09: ff1100013e78cac0
R10: ffac800000cd7980 R11: ff1100013e12b1f0 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: ff1100011a99a2ec
FS:  00007fbd7086f740(0000) GS:ff1100013fd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000200071c0 CR3: 0000000118556004 CR4: 0000000000771ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe07f0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 <TASK>
 proc_create_net_single+0x144/0x210 fs/proc/proc_net.c:220
 bcm_connect+0x472/0x840 net/can/bcm.c:1673
 __sys_connect_file net/socket.c:2049 [inline]
 __sys_connect+0x5d2/0x690 net/socket.c:2066
 __do_sys_connect net/socket.c:2076 [inline]
 __se_sys_connect net/socket.c:2073 [inline]
 __x64_sys_connect+0x8f/0x100 net/socket.c:2073
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xd9/0x1c0 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7fbd708b0e5d
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 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 8b 0d 73 9f 1b 00 f7 d8 64 89 01 48
RSP: 002b:00007fff8cd33f08 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fbd708b0e5d
RDX: 0000000000000010 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000040 R09: 0000000000000040
R10: 0000000000000040 R11: 0000000000000246 R12: 00007fff8cd34098
R13: 0000000000401280 R14: 0000000000406de8 R15: 00007fbd70ab9000
 </TASK>
remove_proc_entry: removing non-empty directory 'net/can-bcm', leaking at least '2456'

The Linux kernel CVE team has assigned CVE-2024-46771 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 4.19.322 with commit 5c680022c4e2
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 5.4.284 with commit 33ed4ba73caa
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 5.10.226 with commit aec92dbebdbe
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 5.15.167 with commit 10bfacbd5e8d
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 6.1.110 with commit 3b39dc2901aa
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 6.6.51 with commit 4377b79323df
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 6.10.10 with commit abb0a615569e
	Issue introduced in 2.6.25 with commit ffd980f976e7 and fixed in 6.11 with commit 76fe372ccb81

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2024-46771
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	net/can/bcm.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/5c680022c4e28ba18ea500f3e29f0428271afa92
	https://git.kernel.org/stable/c/33ed4ba73caae39f34ab874ba79138badc2c65dd
	https://git.kernel.org/stable/c/aec92dbebdbec7567d9f56d7c9296a572b8fd849
	https://git.kernel.org/stable/c/10bfacbd5e8d821011d857bee73310457c9c989a
	https://git.kernel.org/stable/c/3b39dc2901aa7a679a5ca981a3de9f8d5658afe8
	https://git.kernel.org/stable/c/4377b79323df62eb5d310354f19b4d130ff58d50
	https://git.kernel.org/stable/c/abb0a615569ec008e8a93d9f3ab2d5b418ea94d4
	https://git.kernel.org/stable/c/76fe372ccb81b0c89b6cd2fec26e2f38c958be85