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SubjectRe: [PATCH 1/3] extend get/setrlimit to support setting rlimits external to a process (v7)
    Modify setrlimit syscall to accomodate various usages.

Split the sys_setrlimit syscall into two parts:
1) a DEFINE_SYSCALL wrapper that implements the sys_setrlimit function
2) a core do_setrlimit function that accepts as a parameter a task on which to
operate on the limits of

This allows us later to implement sys_setprlimit, which allows us to change the
limits of any process from userspace

Signed-off-by: Neil Horman <nhorman@tuxdriver.com


include/linux/sched.h | 3 +++
kernel/sys.c | 48 ++++++++++++++++++++++++++++++------------------
2 files changed, 33 insertions(+), 18 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 7755763..ce95005 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -672,6 +672,9 @@ struct signal_struct {
int oom_adj; /* OOM kill score adjustment (bit shift) */
};

+extern int do_setrlimit(unsigned int resource, struct rlimit *new_rlim,
+ struct task_struct *tsk);
+
/* Context switch must be unlocked if interrupts are to be enabled */
#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW
# define __ARCH_WANT_UNLOCKED_CTXSW
diff --git a/kernel/sys.c b/kernel/sys.c
index 1828f8d..0e210a4 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1238,41 +1238,41 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,

#endif

-SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
+int do_setrlimit(unsigned int resource, struct rlimit *new_rlim,
+ struct task_struct *tsk)
{
- struct rlimit new_rlim, *old_rlim;
int retval;
+ struct rlimit *old_rlim;

- if (resource >= RLIM_NLIMITS)
- return -EINVAL;
- if (copy_from_user(&new_rlim, rlim, sizeof(*rlim)))
- return -EFAULT;
- if (new_rlim.rlim_cur > new_rlim.rlim_max)
+
+ 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) &&
+ old_rlim = tsk->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)
+
+ if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
return -EPERM;

- retval = security_task_setrlimit(resource, &new_rlim);
+ retval = security_task_setrlimit(resource, new_rlim);
if (retval)
return retval;

- if (resource == RLIMIT_CPU && new_rlim.rlim_cur == 0) {
+ if (resource == RLIMIT_CPU && new_rlim->rlim_cur == 0) {
/*
* The caller is asking for an immediate RLIMIT_CPU
* expiry. But we use the zero value to mean "it was
* never set". So let's cheat and make it one second
* instead
*/
- new_rlim.rlim_cur = 1;
+ new_rlim->rlim_cur = 1;
}

- task_lock(current->group_leader);
- *old_rlim = new_rlim;
- task_unlock(current->group_leader);
+ task_lock(tsk->group_leader);
+ *old_rlim = *new_rlim;
+ task_unlock(tsk->group_leader);

if (resource != RLIMIT_CPU)
goto out;
@@ -1283,14 +1283,26 @@ SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
* very long-standing error, and fixing it now risks breakage of
* applications, so we live with it
*/
- if (new_rlim.rlim_cur == RLIM_INFINITY)
+ if (new_rlim->rlim_cur == RLIM_INFINITY)
goto out;

- update_rlimit_cpu(new_rlim.rlim_cur);
+ update_rlimit_cpu(new_rlim->rlim_cur);
out:
return 0;
}

+SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
+{
+ struct rlimit new_rlim;
+
+ if (resource >= RLIM_NLIMITS)
+ return -EINVAL;
+ if (copy_from_user(&new_rlim, rlim, sizeof(*rlim)))
+ return -EFAULT;
+
+ return do_setrlimit(resource, &new_rlim, current);
+}
+
/*
* It would make sense to put struct rusage in the task_struct,
* except that would make the task_struct be *really big*. After

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