linux-kernel - Re: [PATCH] crypto: ccp - Fix crash when rebind ccp device for ccp.ko

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Message-ID: <CADs4wpXGJpm7L2nOpvdKv2U0TZNizEqku_HBzAJ-gn86XAPRMQ@mail.gmail.com>
Date: Tue, 24 Jun 2025 14:04:54 +0800
From: 1998 Xisme <xisme1998@...il.com>
To: Tom Lendacky <thomas.lendacky@....com>, herbert@...dor.apana.org.au, 
	davem@...emloft.net
Cc: john.allen@....com, linux-kernel@...r.kernel.org, 
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH] crypto: ccp - Fix crash when rebind ccp device for ccp.ko

You're right. But I checked with checkpatch.pl and it reported:

WARNING: debugfs_remove_recursive(NULL) is safe and this check is
probably not required
#70: FILE: drivers/crypto/ccp/ccp-debugfs.c:324:
+       if (ccp_debugfs_dir) {
+               debugfs_remove_recursive(ccp_debugfs_dir);

Perhaps we could simplify it to:

        mutex_lock(&ccp_debugfs_lock);
        debugfs_remove_recursive(ccp_debugfs_dir);
        ccp_debugfs_dir = NULL;
        mutex_unlock(&ccp_debugfs_lock);

I'll send a v2 patch soon.

Tom Lendacky <thomas.lendacky@....com> 于2025年6月24日周二 01:17写道：
>
> On 6/23/25 01:25, Mengbiao Xiong wrote:
> > When CONFIG_CRYPTO_DEV_CCP_DEBUGFS is enabled, rebinding
> > the ccp device causes the following crash:
> >
> > $ echo '0000:0a:00.2' > /sys/bus/pci/drivers/ccp/unbind
> > $ echo '0000:0a:00.2' > /sys/bus/pci/drivers/ccp/bind
> >
> > [  204.976930] BUG: kernel NULL pointer dereference, address: 0000000000000098
> > [  204.978026] #PF: supervisor write access in kernel mode
> > [  204.979126] #PF: error_code(0x0002) - not-present page
> > [  204.980226] PGD 0 P4D 0
> > [  204.981317] Oops: Oops: 0002 [#1] SMP NOPTI
> > ...
> > [  204.997852] Call Trace:
> > [  204.999074]  <TASK>
> > [  205.000297]  start_creating+0x9f/0x1c0
> > [  205.001533]  debugfs_create_dir+0x1f/0x170
> > [  205.002769]  ? srso_return_thunk+0x5/0x5f
> > [  205.004000]  ccp5_debugfs_setup+0x87/0x170 [ccp]
> > [  205.005241]  ccp5_init+0x8b2/0x960 [ccp]
> > [  205.006469]  ccp_dev_init+0xd4/0x150 [ccp]
> > [  205.007709]  sp_init+0x5f/0x80 [ccp]
> > [  205.008942]  sp_pci_probe+0x283/0x2e0 [ccp]
> > [  205.010165]  ? srso_return_thunk+0x5/0x5f
> > [  205.011376]  local_pci_probe+0x4f/0xb0
> > [  205.012584]  pci_device_probe+0xdb/0x230
> > [  205.013810]  really_probe+0xed/0x380
> > [  205.015024]  __driver_probe_device+0x7e/0x160
> > [  205.016240]  device_driver_attach+0x2f/0x60
> > [  205.017457]  bind_store+0x7c/0xb0
> > [  205.018663]  drv_attr_store+0x28/0x40
> > [  205.019868]  sysfs_kf_write+0x5f/0x70
> > [  205.021065]  kernfs_fop_write_iter+0x145/0x1d0
> > [  205.022267]  vfs_write+0x308/0x440
> > [  205.023453]  ksys_write+0x6d/0xe0
> > [  205.024616]  __x64_sys_write+0x1e/0x30
> > [  205.025778]  x64_sys_call+0x16ba/0x2150
> > [  205.026942]  do_syscall_64+0x56/0x1e0
> > [  205.028108]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
> > [  205.029276] RIP: 0033:0x7fbc36f10104
> > [  205.030420] Code: 89 02 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 8d 05 e1 08 2e 00 8b 00 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 f3 c3 66 90 41 54 55 49 89 d4 53 48 89 f5
> >
> > This patch sets ccp_debugfs_dir to NULL after destroying it in
> > ccp5_debugfs_destroy, allowing the directory dentry to be
> > recreated when rebinding the ccp device.
> >
> > Tested on AMD Ryzen 7 1700X.
> >
> > Fixes: 3cdbe346ed3f ("crypto: ccp - Add debugfs entries for CCP information")
> > Signed-off-by: Mengbiao Xiong <xisme1998@...il.com>
> > ---
> >  drivers/crypto/ccp/ccp-debugfs.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/crypto/ccp/ccp-debugfs.c b/drivers/crypto/ccp/ccp-debugfs.c
> > index a1055554b..0d432f3c4 100644
> > --- a/drivers/crypto/ccp/ccp-debugfs.c
> > +++ b/drivers/crypto/ccp/ccp-debugfs.c
> > @@ -320,4 +320,5 @@ void ccp5_debugfs_setup(struct ccp_device *ccp)
> >  void ccp5_debugfs_destroy(void)
> >  {
> >       debugfs_remove_recursive(ccp_debugfs_dir);
> > +     ccp_debugfs_dir = NULL;
>
> Hmmm... it seems like this should be protected by the mutex similar to how
> ccp5_debugfs_setup() is, right?
>
> Maybe something like:
>
>         mutex_lock(&ccp_debugfs_lock);
>         if (ccp_debugfs_dir) {
>                 debugfs_remove_recursive(ccp_debugfs_dir);
>                 ccp_debugfs_dir = NULL;
>         }
>         mutex_unlock(&ccp_debugfs_lock);
>
> That should also fix the issue, thoughts?
>
> Thanks,
> Tom
>
> >  }