Subject: Re: [PATCH] brcmfmac: abort and release host after error

From: Dan Carpenter <[email-masked]>
Date: Wed, 29 Jan 2020 06:32:57 +0300

On Tue, Jan 28, 2020 at 02:14:57PM -0800, Guenter Roeck wrote:
> With commit 216b44000ada ("brcmfmac: Fix use after free in
> brcmf_sdio_readframes()") applied, we see locking timeouts in
> brcmf_sdio_watchdog_thread().
> 
> brcmfmac: brcmf_escan_timeout: timer expired
> INFO: task brcmf_wdog/mmc1:621 blocked for more than 120 seconds.
> Not tainted 4.19.94-07984-g24ff99a0f713 #1
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> brcmf_wdog/mmc1 D    0   621      2 0x00000000 last_sleep: 2440793077.  last_runnable: 2440766827
> [<c0aa1e60>] (__schedule) from [<c0aa2100>] (schedule+0x98/0xc4)
> [<c0aa2100>] (schedule) from [<c0853830>] (__mmc_claim_host+0x154/0x274)
> [<c0853830>] (__mmc_claim_host) from [<bf10c5b8>] (brcmf_sdio_watchdog_thread+0x1b0/0x1f8 [brcmfmac])
> [<bf10c5b8>] (brcmf_sdio_watchdog_thread [brcmfmac]) from [<c02570b8>] (kthread+0x178/0x180)
> 
> In addition to restarting or exiting the loop, it is also necessary to
> abort the command and to release the host.
> 
> Fixes: 216b44000ada ("brcmfmac: Fix use after free in brcmf_sdio_readframes()")

Huh...  Thanks for fixing the bug.  That seems to indicate that we were
triggering the use after free but no one noticed at runtime.  With
kfree(), a use after free can be harmless if you don't have poisoning
enabled and no other thread has re-used the memory.  I'm not sure about
kfree_skb() but presumably it's the same.

Acked-by: Dan Carpenter <[email-masked]>

regards,
dan carpenter