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

["syzbot" <syzbot@kernel.org>]

From: Aleksandr Nogikh <nogikh@google.com>

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@syzkaller.appspotmail.com
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@google.com>

---
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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