Re: [PATCH] firewire: ohci: fix NULL pointer dereference in ar_context_release

[Takashi Sakamoto]

Hi,

On Fri, Aug 07, 2026 at 02:25:26PM +0000, syzbot wrote:
> From: Aleksandr Nogikh <nogikh@xxxxxxxxxx>
> 
> During the error handling path of the driver's probe function, a NULL
> pointer dereference can occur in ar_context_release().
> 
> When pci_probe() fails early (e.g., if pcim_enable_device() or MMIO mapping
> fails), the devres cleanup mechanism invokes release_ohci(). This function
> unconditionally calls ar_context_release() to clean up the asynchronous
> receive contexts. However, if ar_context_init() was not yet called,
> ctx->ohci remains NULL (as the fw_ohci structure is zero-initialized by
> devres_alloc()).
> 
> ar_context_release() immediately dereferences ctx->ohci to get the dev
> pointer before checking if the context was actually initialized, leading to
> a crash:
> 
> Oops: general protection fault, probably for non-canonical address
> 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
> KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
> RIP: 0010:ar_context_release+0x3f/0x380 drivers/firewire/ohci.c:543
> Call Trace:
>  release_ohci+0x3f/0x60 drivers/firewire/ohci.c:3567
>  release_nodes drivers/base/devres.c:546 [inline]
>  devres_release_all+0x1a8/0x260 drivers/base/devres.c:576
>  device_unbind_cleanup drivers/base/dd.c:597 [inline]
>  really_probe+0x451/0xae0 drivers/base/dd.c:772
> 
> To fix this, move the assignment of the dev pointer after the !ctx->buffer
> check. If ctx->buffer is NULL, it indicates that the context was never
> successfully initialized and there is nothing to release, safely avoiding
> the dereference of the uninitialized ctx->ohci pointer.
> 
> Fixes: 5716e58aecdd ("firewire: ohci: release buffer for AR req/resp contexts when managed resource is released")
> Assisted-by: Gemini:gemini-3.5-flash Gemini:gemini-3.1-pro-preview syzbot
> Reported-by: syzbot+d30aad27833a559defab@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=d30aad27833a559defab
> Link: https://syzkaller.appspot.com/ai_job?id=10a18617-7893-42dd-bf1c-cd49e19e95d9
> Signed-off-by: Aleksandr Nogikh <nogikh@xxxxxxxxxx>

Applied to for-linus branch.


Thanks

Takashi Sakamoto