Re: [PATCH] crypto: qat: fix double free in qat_uclo_create_batch_init_list

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Jul 13, 2020 at 07:06:34AM -0700, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis flags this error
> 
> qat_uclo.c:297:3: warning: Attempt to free released memory
>   [unix.Malloc]
>                 kfree(*init_tab_base);
>                 ^~~~~~~~~~~~~~~~~~~~~
> 
> When input *init_tab_base is null, the function allocates memory for
> the head of the list.  When there is problem allocating other list
> elements the list is unwound and freed.  Then a check is made if the
> list head was allocated and is also freed.
> 
> Keeping track of the what may need to be freed is the variable 'tail_old'.
> The unwinding/freeing block is
> 
> 	while (tail_old) {
> 		mem_init = tail_old->next;
> 		kfree(tail_old);
> 		tail_old = mem_init;
> 	}
> 
> The problem is that the first element of tail_old is also what was
> allocated for the list head
> 
> 		init_header = kzalloc(sizeof(*init_header), GFP_KERNEL);
> 		...
> 		*init_tab_base = init_header;
> 		flag = 1;
> 	}
> 	tail_old = init_header;
> 
> So *init_tab_base/init_header are freed twice.
> 
> There is another problem.
> When the input *init_tab_base is non null the tail_old is calculated by
> traveling down the list to first non null entry.
> 
> 	tail_old = init_header;
> 	while (tail_old->next)
> 		tail_old = tail_old->next;
> 
> When the unwinding free happens, the last entry of the input list will
> be freed.
> 
> So the freeing needs a general changed.
> If locally allocated the first element of tail_old is freed, else it
> is skipped.  As a bit of cleanup, reset *init_tab_base if it came in
> as null.
> 
> Fixes: b4b7e67c917f ("crypto: qat - Intel(R) QAT ucode part of fw loader")
> 
> Signed-off-by: Tom Rix <trix@redhat.com>
> ---
>  drivers/crypto/qat/qat_common/qat_uclo.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>