On 1/7/20 8:29 AM, Dan Carpenter wrote:
Hello Petr Mladek,
The patch e91c2518a5d2: "livepatch: Initialize shadow variables
safely by a custom callback" from Apr 16, 2018, leads to the
following static checker warning:
samples/livepatch/livepatch-shadow-fix1.c:86 livepatch_fix1_dummy_alloc()
error: 'klp_shadow_alloc()' 'leak' too small (4 vs 8)
samples/livepatch/livepatch-shadow-fix1.c
53 static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
54 {
55 void **shadow_leak = shadow_data;
56 void *leak = ctor_data;
57
58 *shadow_leak = leak;
59 return 0;
60 }
61
62 static struct dummy *livepatch_fix1_dummy_alloc(void)
63 {
64 struct dummy *d;
65 void *leak;
66
67 d = kzalloc(sizeof(*d), GFP_KERNEL);
68 if (!d)
69 return NULL;
70
71 d->jiffies_expire = jiffies +
72 msecs_to_jiffies(1000 * EXPIRE_PERIOD);
73
74 /*
75 * Patch: save the extra memory location into a SV_LEAK shadow
76 * variable. A patched dummy_free routine can later fetch this
77 * pointer to handle resource release.
78 */
79 leak = kzalloc(sizeof(int), GFP_KERNEL);
80 if (!leak) {
81 kfree(d);
82 return NULL;
83 }
84
85 klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
^^^^^^^^^^^^
This doesn't seem right at all? Leak is a pointer. Why is leak a void
pointer instead of an int pointer?
Hi Dan,
If I remember this code correctly, the shadow variable is tracking the
pointer value itself and not its contents, so sizeof(leak) should be
correct for the shadow variable data size.
(For kernel/livepatch/shadow.c :: __klp_shadow_get_or_alloc() creates
new struct klp_shadow with .data[size] to accommodate its meta-data plus
the desired data).
Why isn't leak an int pointer? I don't remember why, according to git
history it's been that way since the beginning. I think it was coded to
say, "Give me some storage, any size an int will do. I'm not going to
touch it, but I want to demonstrate a memory leak".
Would modifying the pointer type satisfy the static code complaint?
Since the warning is about a size mismatch, what are the parameters that
it is keying on? Does it expect to see the typical allocation pattern like:
int *foo = alloc(sizeof(*foo))
and not:
int *foo = alloc(sizeof(foo))
Thanks,
-- Joe
86 shadow_leak_ctor, leak);
87
88 pr_info("%s: dummy @ %p, expires @ %lx\n",
89 __func__, d, d->jiffies_expire);
90
91 return d;
92 }
regards,
dan carpenter
