Re: [PATCH] [RFC PATCH] ALSA: usb-audio: endpoint: Prevent NULL pointer deference in snd_usb_endpoint_close

["Rajashekar Kuruva (Temp)" <quic_kuruva@xxxxxxxxxxx>]

On 4/26/2024 6:13 PM, Takashi Iwai wrote:
> On Fri, 26 Apr 2024 14:25:11 +0200,
> Rajashekar kuruva wrote:
> > When multiple plug-in and plug-out events occur,
> > there is a risk of encountering a NULL pointer dereference
> > leading to a kernel panic during a headset use-case.
> > this issue arises in the snd_usb_endpoint_close function
> Such a scenario can't happen: ep->iface_ref is changed only in
> chip->mutex lock, hence it can't be NULL there.
>
>
> thanks,
>
> Takashi

Hi Takashi,

Actually we are facing NULL pointer deference while running headset case 
when i checked call trace the last running function is 
snd_usb_endpoint_close where iface_ref and clock_ref both are 0x0

[75703.933104][T10585] Unable to handle kernel NULL pointer dereference 
at virtual address 0000000000000004
[75703.933113][T10585] [RB/E]rb_sreason_str_set: sreason_str set NULL 
pointer dereference
[75703.933116][T10585] Mem abort info:
[75703.933117][T10585]   ESR = 0x0000000096000005
[75703.933119][T10585]   EC = 0x25: DABT (current EL), IL = 32 bits
[75703.933120][T10585]   SET = 0, FnV = 0
[75703.933121][T10585]   EA = 0, S1PTW = 0
[75703.933123][T10585]   FSC = 0x05: level 1 translation fault
[75703.933124][T10585] Data abort info:
[75703.933124][T10585]   ISV = 0, ISS = 0x00000005
[75703.933125][T10585]   CM = 0, WnR = 0
…
[75703.933676][T10585] CPU: 3 PID: 10585 Comm: kworker/u17:0 Tainted: G 
S      W  OE 6.1.43-android14-11-ga2fa77d36d26-ab11204829 #1
[75703.933697][T10585] pstate: 62400005 (nZCv daif +PAN -UAO +TCO -DIT 
-SSBS BTYPE=--)
[75703.933700][T10585] pc : snd_usb_endpoint_close+0x30/0x104
[75703.933721][T10585] lr : snd_usb_endpoint_close+0x28/0x104
[75703.933724][T10585] sp : ffffffc04b2bb740
[75703.933725][T10585] x29: ffffffc04b2bb740 x28: ffffff8024e3ba78 x27: 
ffffffd266e91da0
[75703.933728][T10585] x26: ffffffc04b2bb7a8 x25: ffffff89bec5be00 x24: 
00000000ffffffea
[75703.933730][T10585] x23: 0000000000000002 x22: ffffff885d568008 x21: 
ffffff8024e3ba78
[75703.933732][T10585] x20: ffffff885d568000 x19: ffffff8024e3bb18 x18: 
ffffffd26db2d140
[75703.933734][T10585] x17: 00000000f01b0818 x16: 00000000f01b0818 x15: 
0000000000000008
[75703.933736][T10585] x14: ffffff8a3e2b5780 x13: ffffff8a3e2b5780 x12: 
ffffffd26cbd2770
[75703.933738][T10585] x11: 0000000000000001 x10: ffffff8984320000 x9 : 
4f43b86e946b4e00
[75703.933740][T10585] x8 : 0000000000000000 x7 : 0000000000000001 x6 : 
fffffffdef8e8b70
[75703.933742][T10585] x5 : 0000000000000001 x4 : 0000000000000000 x3 : 
ffffff8024e3bb28
[75703.933743][T10585] x2 : 00000001011fa7c9 x1 : ffffffc04b2bb680 x0 : 
0000000000000000
[75703.933746][T10585] Call trace:
[75703.933747][T10585]  snd_usb_endpoint_close+0x30/0x104

That's why I have added the NULL pointer check

Thanks,

Rajashekar K.