linux-hardening - Re: [PATCH] ext4: Fix function prototype mismatch for ext4_feat

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Message-ID: <Y7UgGSoeB+3yQD8V@sol.localdomain>
Date:   Tue, 3 Jan 2023 22:43:37 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     tytso@....edu, Andreas Dilger <adilger.kernel@...ger.ca>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, llvm@...ts.linux.dev,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix function prototype mismatch for ext4_feat_ktype

On Wed, Jan 04, 2023 at 12:23:44AM +0000, Eric Biggers wrote:
> I'm also surprised that this wasn't found earlier.  Is it possible that CFI does
> not actually distinguish between the two function prototypes here?
> 

It's because this code is only reached when ext4 is a loadable module and it is
being unloaded.  I can reproduce the CFI failure by doing that.

In addition to the naming tweak I requested, can you also add Fixes and Cc
stable tags?

By the way, here's the log from the CFI failure I got:

[   16.412498] CFI failure at kobject_put+0xbb/0x1b0 (target: kfree+0x0/0x180; expected type: 0x7c4aa698)
[   16.413716] invalid opcode: 0000 [#1] PREEMPT SMP
[   16.414299] CPU: 2 PID: 179 Comm: rmmod Tainted: G                T  6.2.0-rc2 #28
[   16.415223] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.1-1-1 04/01/2014
[   16.416383] RIP: 0010:kobject_put+0xbb/0x1b0
[   16.416926] Code: df e8 f9 03 00 00 4d 85 e4 74 24 49 83 3c 24 00 74 1d 0f 1f 44 00 00 48 89 df 4d 8b 1c 24 41 ba 68 59 b5 9
[   16.419199] RSP: 0018:ffffc90000283e20 EFLAGS: 00010a13
[   16.419842] RAX: 0000000000000000 RBX: ffff88800436c9c0 RCX: 0000000000000000
[   16.420719] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88800436c9c0
[   16.421595] RBP: ffffc90000283e40 R08: 0000000000000000 R09: 0000000000000000
[   16.422465] R10: 0000000017461662 R11: ffffffff81216a20 R12: ffffffffa00f9510
[   16.423330] R13: 0000000000000000 R14: ffff88800436ca80 R15: ffff888007643950
[   16.424207] FS:  00007f7bf573f740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
[   16.425188] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   16.425814] CR2: 0000561eb661f818 CR3: 00000000074c9000 CR4: 00000000003506e0
[   16.426574] Call Trace:
[   16.426862]  <TASK>
[   16.427098]  ext4_exit_sysfs+0x14/0x60 [ext4]
[   16.427604]  cleanup_module+0x67/0xedb [ext4]
[   16.428099]  __se_sys_delete_module+0x22d/0x3e0
[   16.428593]  ? syscall_enter_from_user_mode+0x2a/0x1d0
[   16.429142]  ? syscall_enter_from_user_mode+0x2a/0x1d0
[   16.429694]  __x64_sys_delete_module+0x11/0x20
[   16.430173]  do_syscall_64+0x53/0xb0
[   16.430562]  entry_SYSCALL_64_after_hwframe+0x63/0xcd
[   16.431151] RIP: 0033:0x7f7bf584ccfb
[   16.431544] Code: 73 01 c3 48 8b 0d 8d f0 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 8
[   16.433517] RSP: 002b:00007fff7d959068 EFLAGS: 00000206 ORIG_RAX: 00000000000000b0
[   16.434327] RAX: ffffffffffffffda RBX: 0000561eb6615750 RCX: 00007f7bf584ccfb
[   16.435090] RDX: 0000000000000000 RSI: 0000000000000800 RDI: 0000561eb66157b8
[   16.435852] RBP: 0000000000000000 R08: 1999999999999999 R09: 0000000000000000
[   16.436617] R10: 00007f7bf58c2ac0 R11: 0000000000000206 R12: 0000000000000000
[   16.437472] R13: 00007fff7d9592d0 R14: 00007fff7d959d80 R15: 0000561eb66152a0
[   16.438307]  </TASK>
[   16.438552] Modules linked in: ext4(-) crc32c_generic mbcache crc16 jbd2
[   16.439321] ---[ end trace 0000000000000000 ]---
[   16.439829] RIP: 0010:kobject_put+0xbb/0x1b0
[   16.440294] Code: df e8 f9 03 00 00 4d 85 e4 74 24 49 83 3c 24 00 74 1d 0f 1f 44 00 00 48 89 df 4d 8b 1c 24 41 ba 68 59 b5 9
[   16.442310] RSP: 0018:ffffc90000283e20 EFLAGS: 00010a13
[   16.442960] RAX: 0000000000000000 RBX: ffff88800436c9c0 RCX: 0000000000000000
[   16.443719] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88800436c9c0
[   16.444472] RBP: ffffc90000283e40 R08: 0000000000000000 R09: 0000000000000000
[   16.445231] R10: 0000000017461662 R11: ffffffff81216a20 R12: ffffffffa00f9510
[   16.446012] R13: 0000000000000000 R14: ffff88800436ca80 R15: ffff888007643950
[   16.446779] FS:  00007f7bf573f740(0000) GS:ffff88807dd00000(0000) knlGS:0000000000000000
[   16.447658] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   16.448276] CR2: 0000561eb661f818 CR3: 00000000074c9000 CR4: 00000000003506e0