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

#syz upstream


On Fri, Aug 7, 2026 at 12:09 PM 'syzbot' via
syzkaller-upstream-moderation
<[email protected]> wrote:
>
> 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: [email protected]
> Closes: https://syzkaller.appspot.com/bug?extid=d30aad27833a559defab
> Link: https://syzkaller.appspot.com/ai_job?id=10a18617-7893-42dd-bf1c-cd49e19e95d9
> To: <[email protected]>
> To: "Takashi Sakamoto" <[email protected]>
> Cc: <[email protected]>
>
> ---
> diff --git a/drivers/firewire/ohci.c b/drivers/firewire/ohci.c
> index 8153d62c5..e947227e0 100644
> --- a/drivers/firewire/ohci.c
> +++ b/drivers/firewire/ohci.c
> @@ -540,11 +540,13 @@ static void ar_context_link_page(struct ar_context *ctx, unsigned int index)
>
>  static void ar_context_release(struct ar_context *ctx)
>  {
> -       struct device *dev = ctx->ohci->card.device;
> +       struct device *dev;
>
>         if (!ctx->buffer)
>                 return;
>
> +       dev = ctx->ohci->card.device;
> +
>         for (int i = 0; i < AR_BUFFERS; ++i) {
>                 dma_addr_t dma_addr = ctx->dma_addrs[i];
>                 if (dma_addr)
>
>
> base-commit: 075b74841bd0065a3bda3440873c747938e69b68
> --
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