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authorPetr Mladek <pmladek@suse.com>2018-04-16 13:36:46 +0200
committerJiri Kosina <jkosina@suse.cz>2018-04-17 13:42:48 +0200
commite91c2518a5d22a07642f35d85f39001ad379dae4 (patch)
tree3a794a957564ce90514894263e995fbd27649a8c /samples
parente1c70f32386c4984ed8ca1a7aedb9bbff9ed3414 (diff)
downloadlinux-e91c2518a5d22a07642f35d85f39001ad379dae4.tar.bz2
livepatch: Initialize shadow variables safely by a custom callback
The existing API allows to pass a sample data to initialize the shadow data. It works well when the data are position independent. But it fails miserably when we need to set a pointer to the shadow structure itself. Unfortunately, we might need to initialize the pointer surprisingly often because of struct list_head. It is even worse because the list might be hidden in other common structures, for example, struct mutex, struct wait_queue_head. For example, this was needed to fix races in ALSA sequencer. It required to add mutex into struct snd_seq_client. See commit b3defb791b26ea06 ("ALSA: seq: Make ioctls race-free") and commit d15d662e89fc667b9 ("ALSA: seq: Fix racy pool initializations") This patch makes the API more safe. A custom constructor function and data are passed to klp_shadow_*alloc() functions instead of the sample data. Note that ctor_data are no longer a template for shadow->data. It might point to any data that might be necessary when the constructor is called. Also note that the constructor is called under klp_shadow_lock. It is an internal spin_lock that synchronizes alloc() vs. get() operations, see klp_shadow_get_or_alloc(). On one hand, this adds a risk of ABBA deadlocks. On the other hand, it allows to do some operations safely. For example, we could add the new structure into an existing list. This must be done only once when the structure is allocated. Reported-by: Nicolai Stange <nstange@suse.de> Signed-off-by: Petr Mladek <pmladek@suse.com> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'samples')
-rw-r--r--samples/livepatch/livepatch-shadow-fix1.c18
-rw-r--r--samples/livepatch/livepatch-shadow-fix2.c6
2 files changed, 19 insertions, 5 deletions
diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index 830c55514f9f..04151c7f2631 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -56,6 +56,21 @@ struct dummy {
unsigned long jiffies_expire;
};
+/*
+ * The constructor makes more sense together with klp_shadow_get_or_alloc().
+ * In this example, it would be safe to assign the pointer also to the shadow
+ * variable returned by klp_shadow_alloc(). But we wanted to show the more
+ * complicated use of the API.
+ */
+static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
+{
+ void **shadow_leak = shadow_data;
+ void *leak = ctor_data;
+
+ *shadow_leak = leak;
+ return 0;
+}
+
struct dummy *livepatch_fix1_dummy_alloc(void)
{
struct dummy *d;
@@ -74,7 +89,8 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
* pointer to handle resource release.
*/
leak = kzalloc(sizeof(int), GFP_KERNEL);
- klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL);
+ klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
+ shadow_leak_ctor, leak);
pr_info("%s: dummy @ %p, expires @ %lx\n",
__func__, d, d->jiffies_expire);
diff --git a/samples/livepatch/livepatch-shadow-fix2.c b/samples/livepatch/livepatch-shadow-fix2.c
index ff9948f0ec00..d6c62844dc15 100644
--- a/samples/livepatch/livepatch-shadow-fix2.c
+++ b/samples/livepatch/livepatch-shadow-fix2.c
@@ -53,17 +53,15 @@ struct dummy {
bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
{
int *shadow_count;
- int count;
/*
* Patch: handle in-flight dummy structures, if they do not
* already have a SV_COUNTER shadow variable, then attach a
* new one.
*/
- count = 0;
shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
- &count, sizeof(count),
- GFP_NOWAIT);
+ sizeof(*shadow_count), GFP_NOWAIT,
+ NULL, NULL);
if (shadow_count)
*shadow_count += 1;