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SubjectRe: [PATCH] random: Check kmalloc return value and give the failed message
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On Tue, 2010-05-18 at 13:23 +0800, Steven Liu wrote:
> Hi, Matt Mackall,
>
> Check kmalloc return value and give the failed message
>
> Signed-off-by: Liu Qi <lingjiujianke@gmail.com>
> ---
> drivers/char/random.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/char/random.c b/drivers/char/random.c
> index 2fd3d39..d1bedeb 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -952,8 +952,11 @@ static void init_std_data(struct entropy_store *r)
> mix_pool_bytes(r, &now, sizeof(now));
> mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
> /* Enable continuous test in fips mode */
> - if (fips_enabled)
> + if (fips_enabled){
> r->last_data = kmalloc(EXTRACT_SIZE, GFP_KERNEL);
> + if(r->last_data == NULL)
> + printk(KERN_ERR "kmalloc memory failed in %s \n", __func__);
> + }

This is the wrong fix. I'm not sure how this kmalloc got in; I'm sure I
objected to it the first time around. The right answer is: use a static
buffer because a) it can't fail so no error-checking is needed and b)
EXTRACT_SIZE is only 10 bytes! That means that allocating it dynamically
as above takes more code space than you'd be saving by not allocating
it, even without the printk. Here's a better patch:

diff -r a12387bbcc93 drivers/char/random.c
--- a/drivers/char/random.c Thu Apr 08 10:02:02 2010 -0700
+++ b/drivers/char/random.c Tue May 18 00:38:04 2010 -0500
@@ -414,7 +414,7 @@
unsigned add_ptr;
int entropy_count;
int input_rotate;
- __u8 *last_data;
+ __u8 last_data[EXTRACT_SIZE];
};

static __u32 input_pool_data[INPUT_POOL_WORDS];
@@ -862,7 +862,7 @@
while (nbytes) {
extract_buf(r, tmp);

- if (r->last_data) {
+ if (fips_enabled) {
spin_lock_irqsave(&r->lock, flags);
if (!memcmp(tmp, r->last_data, EXTRACT_SIZE))
panic("Hardware RNG duplicated output!\n");
@@ -951,9 +951,6 @@
now = ktime_get_real();
mix_pool_bytes(r, &now, sizeof(now));
mix_pool_bytes(r, utsname(), sizeof(*(utsname())));
- /* Enable continuous test in fips mode */
- if (fips_enabled)
- r->last_data = kmalloc(EXTRACT_SIZE, GFP_KERNEL);
}

static int rand_initialize(void)

>


--
Mathematics is the supreme nostalgia of our time.




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