[PATCH] kvm: properly check debugfs dentry before using it

[PATCH] kvm: properly check debugfs dentry before using it

[Greg Kroah-Hartman]

debugfs can now report an error code if something went wrong instead of
just NULL.  So if the return value is to be used as a "real" dentry, it
needs to be checked if it is an error before dereferencing it.

This is now happening because of ff9fb72bc077 ("debugfs: return error
values, not NULL").  syzbot has found a way to trigger multiple debugfs
files attempting to be created, which fails, and then the error code
gets passed to dentry_path_raw() which obviously does not like it.

Reported-by: Eric Biggers <ebiggers@kernel.org>
Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

Linus, this should go in before 5.0-final is out, as it resolves a
problem found by syzbot.  Paolo has given his ack for me to send this
directly to you.  If you want this in [GIT PULL] format, I can do that
as well.

 virt/kvm/kvm_main.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(uns
 	}
 	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
 
-	if (kvm->debugfs_dentry) {
+	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
 		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
 
 		if (p) {

Re: [PATCH] kvm: properly check debugfs dentry before using it

[Linus Torvalds]

On Thu, Feb 28, 2019 at 7:34 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> Linus, this should go in before 5.0-final is out, as it resolves a
> problem found by syzbot.  Paolo has given his ack for me to send this
> directly to you.  If you want this in [GIT PULL] format, I can do that
> as well.

Applied, thanks,

           Linus

Re: [PATCH] kvm: properly check debugfs dentry before using it

[Eric Biggers]

On Thu, Feb 28, 2019 at 04:34:37PM +0100, Greg Kroah-Hartman wrote:
> debugfs can now report an error code if something went wrong instead of
> just NULL.  So if the return value is to be used as a "real" dentry, it
> needs to be checked if it is an error before dereferencing it.
> 
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL").  syzbot has found a way to trigger multiple debugfs
> files attempting to be created, which fails, and then the error code
> gets passed to dentry_path_raw() which obviously does not like it.
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: kvm@vger.kernel.org
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> 
> Linus, this should go in before 5.0-final is out, as it resolves a
> problem found by syzbot.  Paolo has given his ack for me to send this
> directly to you.  If you want this in [GIT PULL] format, I can do that
> as well.
> 
>  virt/kvm/kvm_main.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(uns
>  	}
>  	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
>  
> -	if (kvm->debugfs_dentry) {
> +	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
>  		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
>  
>  		if (p) {

So what about the other checks of kvm->debugfs_dentry, in
kvm_destroy_vm_debugfs() and kvm_create_vcpu_debugfs()?

- Eric

Re: [PATCH] kvm: properly check debugfs dentry before using it

[Greg Kroah-Hartman]

On Thu, Feb 28, 2019 at 09:17:28AM -0800, Eric Biggers wrote:
> On Thu, Feb 28, 2019 at 04:34:37PM +0100, Greg Kroah-Hartman wrote:
> > debugfs can now report an error code if something went wrong instead of
> > just NULL.  So if the return value is to be used as a "real" dentry, it
> > needs to be checked if it is an error before dereferencing it.
> > 
> > This is now happening because of ff9fb72bc077 ("debugfs: return error
> > values, not NULL").  syzbot has found a way to trigger multiple debugfs
> > files attempting to be created, which fails, and then the error code
> > gets passed to dentry_path_raw() which obviously does not like it.
> > 
> > Reported-by: Eric Biggers <ebiggers@kernel.org>
> > Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> > Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> > Cc: kvm@vger.kernel.org
> > Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > 
> > Linus, this should go in before 5.0-final is out, as it resolves a
> > problem found by syzbot.  Paolo has given his ack for me to send this
> > directly to you.  If you want this in [GIT PULL] format, I can do that
> > as well.
> > 
> >  virt/kvm/kvm_main.c |    2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(uns
> >  	}
> >  	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
> >  
> > -	if (kvm->debugfs_dentry) {
> > +	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
> >  		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
> >  
> >  		if (p) {
> 
> So what about the other checks of kvm->debugfs_dentry, in
> kvm_destroy_vm_debugfs() and kvm_create_vcpu_debugfs()?

Those are fine, they do not matter as they are only calling other
debugfs calls which can handle error codes just fine.  The only issue is
when you try to use the dentry for something "real" like this that bad
things can happen.

Luckily this was only the case in about 4 places in the kernel, all of
which should be fixed now.

thanks,

greg k-h

Re: general protection fault in __dentry_path

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    2137397c92ae Merge tag 'sound-5.0' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1270bf78c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7132344728e7ec3f
dashboard link: https://syzkaller.appspot.com/bug?extid=7857962b4d45e602b8ad
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
userspace arch: i386
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=150bee14c00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f401d4c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 12576 Comm: syz-executor696 Not tainted 5.0.0-rc7+ #81
kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__dentry_path+0x49e/0x7c0 fs/d_path.c:344
Code: 89 fc 41 83 e4 01 44 89 e6 e8 fe e4 b2 ff 45 84 e4 0f 85 04 02 00 00  
e8 b0 e3 b2 ff 48 8b 85 18 ff ff ff 44 89 bd 40 ff ff ff <80> 38 00 0f 85  
f9 02 00 00 48 8b 85 38 ff ff ff 41 83 e7 01 44 89
kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path  
= '/devices/virtual/misc/kvm'
RSP: 0018:ffff888096127c58 EFLAGS: 00010293
RAX: dffffc0000000005 RBX: 0000000000000000 RCX: ffffffff81bcfdc2
RDX: 0000000000000000 RSI: ffffffff81bcfdd0 RDI: 0000000000000001
RBP: ffff888096127d48 R08: ffff88809b17c540 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888096127d20 R14: ffff888092473afe R15: 0000000000014e78
FS:  0000000000000000(0000) GS:ffff8880ae800000(0063) knlGS:00000000f7fe4b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000080fb028 CR3: 000000009de68000 CR4: 00000000001426f0
kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
Call Trace:
kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path  
= '/devices/virtual/misc/kvm'
  dentry_path_raw+0x26/0x30 fs/d_path.c:371
  kvm_uevent_notify_change.part.0+0x213/0x440  
arch/x86/kvm/../../../virt/kvm/kvm_main.c:4051
  kvm_uevent_notify_change arch/x86/kvm/../../../virt/kvm/kvm_main.c:4018  
[inline]
  kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3356  
[inline]
  kvm_dev_ioctl+0x1132/0x1750 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3378
  __do_compat_sys_ioctl fs/compat_ioctl.c:1052 [inline]
  __se_compat_sys_ioctl fs/compat_ioctl.c:998 [inline]
  __ia32_compat_sys_ioctl+0x197/0x620 fs/compat_ioctl.c:998
  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
  do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7fe8869
Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90  
90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90  
90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f7fe41fc EFLAGS: 00000293 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000000ae01
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000003d0f00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 4fe494385b47fe74 ]---
kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
RIP: 0010:__dentry_path+0x49e/0x7c0 fs/d_path.c:344
Code: 89 fc 41 83 e4 01 44 89 e6 e8 fe e4 b2 ff 45 84 e4 0f 85 04 02 00 00  
e8 b0 e3 b2 ff 48 8b 85 18 ff ff ff 44 89 bd 40 ff ff ff <80> 38 00 0f 85  
f9 02 00 00 48 8b 85 38 ff ff ff 41 83 e7 01 44 89
RSP: 0018:ffff888096127c58 EFLAGS: 00010293
RAX: dffffc0000000005 RBX: 0000000000000000 RCX: ffffffff81bcfdc2
RDX: 0000000000000000 RSI: ffffffff81bcfdd0 RDI: 0000000000000001
RBP: ffff888096127d48 R08: ffff88809b17c540 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffff888096127d20 R14: ffff888092473afe R15: 0000000000014e78
kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path  
= '/devices/virtual/misc/kvm'
FS:  0000000000000000(0000) GS:ffff8880ae800000(0063) knlGS:00000000f7fe4b40
CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 00000000080fb038 CR3: 000000009de68000 CR4: 00000000001426f0

Re: general protection fault in __dentry_path

[Eric Biggers]

On Wed, Feb 20, 2019 at 08:14:03PM -0800, syzbot wrote:
> syzbot has found a reproducer for the following crash on:
> 
> HEAD commit:    2137397c92ae Merge tag 'sound-5.0' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1270bf78c00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=7132344728e7ec3f
> dashboard link: https://syzkaller.appspot.com/bug?extid=7857962b4d45e602b8ad
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=150bee14c00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12f401d4c00000
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> 
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 12576 Comm: syz-executor696 Not tainted 5.0.0-rc7+ #81
> kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__dentry_path+0x49e/0x7c0 fs/d_path.c:344
> Code: 89 fc 41 83 e4 01 44 89 e6 e8 fe e4 b2 ff 45 84 e4 0f 85 04 02 00 00
> e8 b0 e3 b2 ff 48 8b 85 18 ff ff ff 44 89 bd 40 ff ff ff <80> 38 00 0f 85 f9
> 02 00 00 48 8b 85 38 ff ff ff 41 83 e7 01 44 89
> kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path =
> '/devices/virtual/misc/kvm'
> RSP: 0018:ffff888096127c58 EFLAGS: 00010293
> RAX: dffffc0000000005 RBX: 0000000000000000 RCX: ffffffff81bcfdc2
> RDX: 0000000000000000 RSI: ffffffff81bcfdd0 RDI: 0000000000000001
> RBP: ffff888096127d48 R08: ffff88809b17c540 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff888096127d20 R14: ffff888092473afe R15: 0000000000014e78
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0063) knlGS:00000000f7fe4b40
> CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00000000080fb028 CR3: 000000009de68000 CR4: 00000000001426f0
> kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
> Call Trace:
> kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path =
> '/devices/virtual/misc/kvm'
>  dentry_path_raw+0x26/0x30 fs/d_path.c:371
>  kvm_uevent_notify_change.part.0+0x213/0x440
> arch/x86/kvm/../../../virt/kvm/kvm_main.c:4051
>  kvm_uevent_notify_change arch/x86/kvm/../../../virt/kvm/kvm_main.c:4018
> [inline]
>  kvm_dev_ioctl_create_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:3356
> [inline]
>  kvm_dev_ioctl+0x1132/0x1750 arch/x86/kvm/../../../virt/kvm/kvm_main.c:3378
>  __do_compat_sys_ioctl fs/compat_ioctl.c:1052 [inline]
>  __se_compat_sys_ioctl fs/compat_ioctl.c:998 [inline]
>  __ia32_compat_sys_ioctl+0x197/0x620 fs/compat_ioctl.c:998
>  do_syscall_32_irqs_on arch/x86/entry/common.c:326 [inline]
>  do_fast_syscall_32+0x281/0xc98 arch/x86/entry/common.c:397
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
> RIP: 0023:0xf7fe8869
> Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90 90
> 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90
> 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
> RSP: 002b:00000000f7fe41fc EFLAGS: 00000293 ORIG_RAX: 0000000000000036
> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000000ae01
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: 00000000003d0f00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> Modules linked in:
> ---[ end trace 4fe494385b47fe74 ]---
> kobject: 'kvm' (00000000985ff3e6): kobject_uevent_env
> RIP: 0010:__dentry_path+0x49e/0x7c0 fs/d_path.c:344
> Code: 89 fc 41 83 e4 01 44 89 e6 e8 fe e4 b2 ff 45 84 e4 0f 85 04 02 00 00
> e8 b0 e3 b2 ff 48 8b 85 18 ff ff ff 44 89 bd 40 ff ff ff <80> 38 00 0f 85 f9
> 02 00 00 48 8b 85 38 ff ff ff 41 83 e7 01 44 89
> RSP: 0018:ffff888096127c58 EFLAGS: 00010293
> RAX: dffffc0000000005 RBX: 0000000000000000 RCX: ffffffff81bcfdc2
> RDX: 0000000000000000 RSI: ffffffff81bcfdd0 RDI: 0000000000000001
> RBP: ffff888096127d48 R08: ffff88809b17c540 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffff888096127d20 R14: ffff888092473afe R15: 0000000000014e78
> kobject: 'kvm' (00000000985ff3e6): fill_kobj_path: path =
> '/devices/virtual/misc/kvm'
> FS:  0000000000000000(0000) GS:ffff8880ae800000(0063) knlGS:00000000f7fe4b40
> CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> CR2: 00000000080fb038 CR3: 000000009de68000 CR4: 00000000001426f0
> 

Hi Greg, this started happening with:

	commit ff9fb72bc07705c00795ca48631f7fffe24d2c6b (HEAD)
	Author: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
	Date:   Wed Jan 23 11:28:14 2019 +0100

	    debugfs: return error values, not NULL

But virt/kvm/kvm_main.c still checks for NULL:

        if (kvm->debugfs_dentry) {
                char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);

                if (p) {
                        tmp = dentry_path_raw(kvm->debugfs_dentry, p, PATH_MAX);
                        if (!IS_ERR(tmp))
                                add_uevent_var(env, "STATS_PATH=%s", tmp);
                        kfree(p);
                }
        }

... and sometimes kvm->debugfs_dentry = ERR_PTR(-EEXIST).

- Eric

[PATCH] kvm: properly check debugfs dentry before using it

[Greg Kroah-Hartman]

debugfs can now report an error code if something went wrong instead of
just NULL.  So if the return value is to be used as a "real" dentry, it
needs to be checked if it is an error before dereferencing it.

This is now happening because of ff9fb72bc077 ("debugfs: return error
values, not NULL").  syzbot has found a way to trigger multiple debugfs
files attempting to be created, which fails, and then the error code
gets passed to dentry_path_raw() which obviously does not like it.

Reported-by: Eric Biggers <ebiggers@kernel.org>
Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---

Paolo, this should be merged into 5.0-final, and if not there, then
5.1-rc1 and then backported to 5.0 through the stable tree.  If you
want me to send this to Linus, I will be glad to do so.


diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 585845203db8..076bc38963bf 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
 	}
 	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
 
-	if (kvm->debugfs_dentry) {
+	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
 		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
 
 		if (p) {

Re: [PATCH] kvm: properly check debugfs dentry before using it

[Paolo Bonzini]

On 28/02/19 16:08, Greg Kroah-Hartman wrote:
> debugfs can now report an error code if something went wrong instead of
> just NULL.  So if the return value is to be used as a "real" dentry, it
> needs to be checked if it is an error before dereferencing it.
> 
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL").  syzbot has found a way to trigger multiple debugfs
> files attempting to be created, which fails, and then the error code
> gets passed to dentry_path_raw() which obviously does not like it.
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> Cc: kvm@vger.kernel.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> ---
> 
> Paolo, this should be merged into 5.0-final, and if not there, then
> 5.1-rc1 and then backported to 5.0 through the stable tree.  If you
> want me to send this to Linus, I will be glad to do so.
> 
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 585845203db8..076bc38963bf 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
>  	}
>  	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
>  
> -	if (kvm->debugfs_dentry) {
> +	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
>  		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
>  
>  		if (p) {
> 

Sure, go ahead.

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

Re: [PATCH] kvm: properly check debugfs dentry before using it

[Greg Kroah-Hartman]

On Thu, Feb 28, 2019 at 04:14:50PM +0100, Paolo Bonzini wrote:
> On 28/02/19 16:08, Greg Kroah-Hartman wrote:
> > debugfs can now report an error code if something went wrong instead of
> > just NULL.  So if the return value is to be used as a "real" dentry, it
> > needs to be checked if it is an error before dereferencing it.
> > 
> > This is now happening because of ff9fb72bc077 ("debugfs: return error
> > values, not NULL").  syzbot has found a way to trigger multiple debugfs
> > files attempting to be created, which fails, and then the error code
> > gets passed to dentry_path_raw() which obviously does not like it.
> > 
> > Reported-by: Eric Biggers <ebiggers@kernel.org>
> > Reported-and-tested-by: syzbot+7857962b4d45e602b8ad@syzkaller.appspotmail.com
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> > Cc: kvm@vger.kernel.org
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > 
> > ---
> > 
> > Paolo, this should be merged into 5.0-final, and if not there, then
> > 5.1-rc1 and then backported to 5.0 through the stable tree.  If you
> > want me to send this to Linus, I will be glad to do so.
> > 
> > 
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 585845203db8..076bc38963bf 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4044,7 +4044,7 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm)
> >  	}
> >  	add_uevent_var(env, "PID=%d", kvm->userspace_pid);
> >  
> > -	if (kvm->debugfs_dentry) {
> > +	if (!IS_ERR_OR_NULL(kvm->debugfs_dentry)) {
> >  		char *tmp, *p = kmalloc(PATH_MAX, GFP_KERNEL);
> >  
> >  		if (p) {
> > 
> 
> Sure, go ahead.
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Wonderful, will do so right now, thanks!

greg k-h