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Subject[PATCH -repost 4/8] sys_setrlimit: make sure ->rlim_max never grows
Date
From: Oleg Nesterov <oleg@redhat.com>

Mostly preparation for Jiri's changes, but probably makes sense anyway.

sys_setrlimit() checks new_rlim.rlim_max <= old_rlim->rlim_max, but when
it takes task_lock() old_rlim->rlim_max can be already lowered. Move this
check under task_lock().

Currently this is not important, we can only race with our sub-thread,
this means the application is stupid. But when we change the code to allow
the update of !current task's limits, it becomes important to make sure
->rlim_max can be lowered "reliably" even if we race with the application
doing sys_setrlimit().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
---
kernel/sys.c | 15 ++++++++-------
1 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/kernel/sys.c b/kernel/sys.c
index b8f9f13..4b3a966 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1249,10 +1249,6 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
return -EFAULT;
if (new_rlim.rlim_cur > new_rlim.rlim_max)
return -EINVAL;
- old_rlim = current->signal->rlim + resource;
- if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
- !capable(CAP_SYS_RESOURCE))
- return -EPERM;
if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
return -EPERM;

@@ -1270,11 +1266,16 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
new_rlim.rlim_cur = 1;
}

+ old_rlim = current->signal->rlim + resource;
task_lock(current->group_leader);
- *old_rlim = new_rlim;
+ if ((new_rlim.rlim_max <= old_rlim->rlim_max) ||
+ capable(CAP_SYS_RESOURCE))
+ *old_rlim = new_rlim;
+ else
+ retval = -EPERM;
task_unlock(current->group_leader);

- if (resource != RLIMIT_CPU)
+ if (retval || resource != RLIMIT_CPU)
goto out;

/*
@@ -1288,7 +1289,7 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)

update_rlimit_cpu(current, new_rlim.rlim_cur);
out:
- return 0;
+ return retval;
}

/*
--
1.6.4.2


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