+ mm-mlock-fix-two-bugs-in-user_shm_lock.patch added to -mm tree

+ mm-mlock-fix-two-bugs-in-user_shm_lock.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: mm/mlock: fix two bugs in user_shm_lock()
has been added to the -mm tree.  Its filename is
     mm-mlock-fix-two-bugs-in-user_shm_lock.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-mlock-fix-two-bugs-in-user_shm_lock.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-mlock-fix-two-bugs-in-user_shm_lock.patch

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------------------------------------------------------
From: Miaohe Lin <linmiaohe@huawei.com>
Subject: mm/mlock: fix two bugs in user_shm_lock()

user_shm_lock forgets to set allowed to 0 when get_ucounts fails.  So the
later user_shm_unlock might do the extra dec_rlimit_ucounts.  Also in the
RLIM_INFINITY case, user_shm_lock will success regardless of the value of
memlock where memblock == LONG_MAX && !capable(CAP_IPC_LOCK) should fail. 
Fix all of these by changing the code to leave lock_limit at ULONG_MAX aka
RLIM_INFINITY, leave "allowed" initialized to 0 and remove the special
case of RLIM_INFINITY as nothing can be greater than ULONG_MAX.

Credit goes to Eric W.  Biederman for proposing simplifying the code and
thus catching the later bug.

Link: https://lkml.kernel.org/r/20220322080918.59861-1-linmiaohe@huawei.com
Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Alexey Gladkov <legion@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/mlock.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/mm/mlock.c~mm-mlock-fix-two-bugs-in-user_shm_lock
+++ a/mm/mlock.c
@@ -721,13 +721,12 @@ int user_shm_lock(size_t size, struct uc
 
 	locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	lock_limit = rlimit(RLIMIT_MEMLOCK);
-	if (lock_limit == RLIM_INFINITY)
-		allowed = 1;
-	lock_limit >>= PAGE_SHIFT;
+	if (lock_limit != RLIM_INFINITY)
+		lock_limit >>= PAGE_SHIFT;
 	spin_lock(&shmlock_user_lock);
 	memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
 
-	if (!allowed && (memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) {
+	if ((memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) {
 		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
 		goto out;
 	}
_

Patches currently in -mm which might be from linmiaohe@huawei.com are

mm-mremap-use-helper-mlock_future_check.patch
mm-mlock-fix-two-bugs-in-user_shm_lock.patch
mm-compaction-use-helper-isolation_suitable.patch