Re: [PATCH] thunderbolt: Fix double free of drom buffer

[Bjorn Helgaas]

On Sun, Apr 10, 2016 at 12:48:27PM +0200, Andreas Noever wrote:
> If tb_drom_read fails sw->drom is freed but not set to NULL. sw->drom
> is then freed again in the error path of sw_switch_alloc.

s/sw_switch_alloc/tb_switch_alloc/ ?

> The bug can be triggered by unplugging a thunderbolt device shortly
> after it is detected by the thunderbolt driver.
> 
> Signed-off-by: Andreas Noever <andreas.noever@xxxxxxxxx>
> Cc: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

How far back would this need to be applied?  What is the commit where
the but was introduced?

I applied this to pci/thunderbolt for v4.7 with the following
changelog.  If I did it wrong, I'll gladly update it, especially if
you have specific symptoms of a bug or oops that would help people
find this fix.

    thunderbolt: Fix double free of drom buffer
    
    If tb_drom_read() fails, sw->drom is freed but not set to NULL.  sw->drom
    is then freed again in the error path of tb_switch_alloc().
    
    The bug can be triggered by unplugging a thunderbolt device shortly after
    it is detected by the thunderbolt driver.
    
    Clear sw->drom if tb_drom_read() fails.
    
    [bhelgaas: add Fixes:, stable versions of interest]
    Fixes: 343fcb8c70d7 ("thunderbolt: Fix nontrivial endpoint devices.")
    Signed-off-by: Andreas Noever <andreas.noever@xxxxxxxxx>
    Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
    CC: stable@xxxxxxxxxxxxxxx	# v3.17+
    CC: Lukas Wunner <lukas@xxxxxxxxx>

> ---
>  drivers/thunderbolt/eeprom.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/thunderbolt/eeprom.c b/drivers/thunderbolt/eeprom.c
> index 0dde34e..545c60c 100644
> --- a/drivers/thunderbolt/eeprom.c
> +++ b/drivers/thunderbolt/eeprom.c
> @@ -444,6 +444,7 @@ int tb_drom_read(struct tb_switch *sw)
>  	return tb_drom_parse_entries(sw);
>  err:
>  	kfree(sw->drom);
> +	sw->drom = NULL;
>  	return -EIO;
>  
>  }
> -- 
> 2.8.0
> 
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