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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.

Fixes: d7c9e99aee ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: stable@vger.kernel.org
v1: https://lkml.kernel.org/r/20220310132417.41189-1-linmiaohe@huawei.com
v2: https://lkml.kernel.org/r/20220314064039.62972-1-linmiaohe@huawei.com
Link: https://lkml.kernel.org/r/20220322080918.59861-1-linmiaohe@huawei.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
This commit is contained in:
Miaohe Lin 2022-03-22 16:09:18 +08:00 committed by Eric W. Biederman
parent ffb217a13a
commit e97824ff66
1 changed files with 3 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
mm/mlock.c
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@ -827,13 +827,12 @@ int user_shm_lock(size_t size, struct ucounts *ucounts)
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;
}