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authorEric W. Biederman <ebiederm@xmission.com>2017-03-05 15:03:22 -0600
committerEric W. Biederman <ebiederm@xmission.com>2017-03-06 15:26:37 -0600
commit040757f738e13caaa9c5078bca79aa97e11dde88 (patch)
treed2254d13ea030261eb3d894f8d7c3401f3e8a5e3 /include
parentc1ae3cfa0e89fa1a7ecc4c99031f5e9ae99d9201 (diff)
ucount: Remove the atomicity from ucount->count
Always increment/decrement ucount->count under the ucounts_lock. The increments are there already and moving the decrements there means the locking logic of the code is simpler. This simplification in the locking logic fixes a race between put_ucounts and get_ucounts that could result in a use-after-free because the count could go zero then be found by get_ucounts and then be freed by put_ucounts. A bug presumably this one was found by a combination of syzkaller and KASAN. JongWhan Kim reported the syzkaller failure and Dmitry Vyukov spotted the race in the code. Cc: stable@vger.kernel.org Fixes: f6b2db1a3e8d ("userns: Make the count of user namespaces per user") Reported-by: JongHwan Kim <zzoru007@gmail.com> Reported-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: Andrei Vagin <avagin@gmail.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/user_namespace.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index be765234c0a2..32354b4b4b2b 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -72,7 +72,7 @@ struct ucounts {
struct hlist_node node;
struct user_namespace *ns;
kuid_t uid;
- atomic_t count;
+ int count;
atomic_t ucount[UCOUNT_COUNTS];
};