linux-kernel - Re: [Bug] WARNING: zero-size vmalloc in sel_write

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Message-ID: <CAHC9VhQ3crxcLXbT3fw2k7jYJFKy1VOm25npKpD9ZrwmwKzvJw@mail.gmail.com>
Date: Mon, 4 Mar 2024 14:19:26 -0500
From: Paul Moore <paul@...l-moore.com>
To: Sam Sun <samsun1006219@...il.com>
Cc: linux-kernel@...r.kernel.org, 
	"xrivendell7@...il.com" <xrivendell7@...il.com>, syzkaller@...glegroups.com, selinux@...r.kernel.org, 
	omosnace@...hat.com
Subject: Re: [Bug] WARNING: zero-size vmalloc in sel_write_load

On Mon, Mar 4, 2024 at 9:08 AM Sam Sun <samsun1006219@...il.com> wrote:
>
> Dear developers and maintainers,
>
> We encountered a warning in function sel_write_load(). It is tested on
> kernel 6.8.0-rc7. Bug report is listed below.
>
> ```
> WARNING: CPU: 1 PID: 8109 at mm/vmalloc.c:3247
> __vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247
> Modules linked in:
> CPU: 1 PID: 8109 Comm: syz-executor370 Not tainted 6.7.0-rc7 #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> RIP: 0010:__vmalloc_node_range+0x10a0/0x1490 mm/vmalloc.c:3247
> Code: 65 48 2b 04 25 28 00 00 00 0f 85 98 02 00 00 48 81 c4 70 01 00
> 00 4c 89 e0 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 71 43 b7 ff 90 <0f> 0b
> 90 45 31 e4 eb a1 e8 63 43 b7 ff 48 8b 4c 24 40 31 f6 45 31
> RSP: 0018:ffffc90002adf9c0 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: dffffc0000000000 RCX: ffffffff81cdc194
> RDX: ffff888022124ec0 RSI: ffffffff81cdd16f RDI: 0000000000000007
> RBP: 0000000000000000 R08: 0000000000000007 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000001 R12: ffff888107373a48
> R13: dffffc0000000000 R14: 0000000000000000 R15: ffffc90002adfec8
> FS:  00005555560953c0(0000) GS:ffff888135c00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000020000010 CR3: 000000010503d000 CR4: 0000000000750ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
>  <TASK>
>  __vmalloc_node mm/vmalloc.c:3385 [inline]
>  vmalloc+0x6b/0x80 mm/vmalloc.c:3418
>  sel_write_load+0x27f/0x19d0 security/selinux/selinuxfs.c:603
>  vfs_write+0x2a9/0xd80 fs/read_write.c:582
>  ksys_pwrite64 fs/read_write.c:699 [inline]
>  __do_sys_pwrite64 fs/read_write.c:709 [inline]
>  __se_sys_pwrite64 fs/read_write.c:706 [inline]
>  __x64_sys_pwrite64+0x1f3/0x250 fs/read_write.c:706
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> RIP: 0033:0x7f40e7728f8d
> Code: 28 c3 e8 46 1e 00 00 66 0f 1f 44 00 00 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 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fff5bf39508 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
> RAX: ffffffffffffffda RBX: 00007fff5bf39708 RCX: 00007f40e7728f8d
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 0000000000000001 R08: 0000000000000000 R09: 00007fff5bf39708
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007fff5bf396f8 R14: 00007f40e77a6530 R15: 0000000000000001
>  </TASK>
> ```
>
> The cause of this bug is that in sel_write_load(), parameter "count"
> is controlled by user, which could be zero. It is passed to vmalloc()
> as an argument.
>
> If you have any questions, please contact us.
> Reported by: Yue Sun <samsun1006219@...il.com>
> Reported by: xingwei lee <xrivendell7@...il.com>

Everything appears to be working as expected, vmalloc() caught the
zero-length allocation request, emitted the warning, returned NULL to
sel_write_load(), and sel_write_load() handled the error condition
triggered by vmalloc(0) returning NULL.  Did you see any unexpected
behavior beyond this warning message above?

-- 
paul-moore.com