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Date: Fri, 7 May 2010 10:55:42 +0200
From: Jiri Slaby <jslaby@...e.cz>
To: akpm@...ux-foundation.org
Cc: torvalds@...ux-foundation.org, adobriyan@...il.com,
nhorman@...driver.com, oleg@...hat.com,
linux-kernel@...r.kernel.org, jirislaby@...il.com
Subject: [PATCH 10/11] rlimits: implement prlimit64 syscall
This patch adds the code to support the sys_prlimit64 syscall which
modifies-and-return the rlim values of a selected process. pid 0 means
current process.
All rlim users now either use accessors or doesn't need them due to
- locking
- the fact a process was just forked and nobody else knows about it
yet (and nobody can't thus read/write limits)
hence it is safe to modify them now.
The limitation is that we stay at ulong internal representation. So
we use the rlim64_is_infinity check where we compare to ULONG_MAX on
32-bit which is the maximal value there.
And since internally we hold limits in struct rlimit, we introduce
converters used before and after do_prlimit call in sys_prlimit64.
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
include/linux/syscalls.h | 4 ++
kernel/sys.c | 99 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 103 insertions(+), 0 deletions(-)
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index f93a5c4..3f0e3ab 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -35,6 +35,7 @@ struct oldold_utsname;
struct old_utsname;
struct pollfd;
struct rlimit;
+struct rlimit64;
struct rusage;
struct sched_param;
struct sel_arg_struct;
@@ -667,6 +668,9 @@ asmlinkage long sys_old_getrlimit(unsigned int resource, struct rlimit __user *r
#endif
asmlinkage long sys_setrlimit(unsigned int resource,
struct rlimit __user *rlim);
+asmlinkage long sys_prlimit64(pid_t pid, unsigned int resource,
+ const struct rlimit64 __user *new_rlim,
+ struct rlimit64 __user *old_rlim);
asmlinkage long sys_getrusage(int who, struct rusage __user *ru);
asmlinkage long sys_umask(int mask);
diff --git a/kernel/sys.c b/kernel/sys.c
index 0f8034f..d7fcd4a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1271,6 +1271,39 @@ SYSCALL_DEFINE2(old_getrlimit, unsigned int, resource,
#endif
+static inline bool rlim64_is_infinity(__u64 rlim64)
+{
+#if BITS_PER_LONG < 64
+ return rlim64 >= ULONG_MAX;
+#else
+ return rlim64 == RLIM64_INFINITY;
+#endif
+}
+
+static void rlim_to_rlim64(const struct rlimit *rlim, struct rlimit64 *rlim64)
+{
+ if (rlim->rlim_cur == RLIM_INFINITY)
+ rlim64->rlim_cur = RLIM64_INFINITY;
+ else
+ rlim64->rlim_cur = rlim->rlim_cur;
+ if (rlim->rlim_max == RLIM_INFINITY)
+ rlim64->rlim_max = RLIM64_INFINITY;
+ else
+ rlim64->rlim_max = rlim->rlim_max;
+}
+
+static void rlim64_to_rlim(const struct rlimit64 *rlim64, struct rlimit *rlim)
+{
+ if (rlim64_is_infinity(rlim64->rlim_cur))
+ rlim->rlim_cur = RLIM_INFINITY;
+ else
+ rlim->rlim_cur = (unsigned long)rlim64->rlim_cur;
+ if (rlim64_is_infinity(rlim64->rlim_max))
+ rlim->rlim_max = RLIM_INFINITY;
+ else
+ rlim->rlim_max = (unsigned long)rlim64->rlim_max;
+}
+
/* make sure you are allowed to change @tsk limits before calling this */
int do_prlimit(struct task_struct *tsk, unsigned int resource,
struct rlimit *new_rlim, struct rlimit *old_rlim)
@@ -1340,6 +1373,72 @@ out:
return retval;
}
+/* rcu lock must be held */
+static int check_prlimit_permission(struct task_struct *task)
+{
+ const struct cred *cred = current_cred(), *tcred;
+
+ tcred = __task_cred(task);
+ if ((cred->uid != tcred->euid ||
+ cred->uid != tcred->suid ||
+ cred->uid != tcred->uid ||
+ cred->gid != tcred->egid ||
+ cred->gid != tcred->sgid ||
+ cred->gid != tcred->gid) &&
+ !capable(CAP_SYS_RESOURCE)) {
+ return -EPERM;
+ }
+
+ return 0;
+}
+
+SYSCALL_DEFINE4(prlimit64, pid_t, pid, unsigned int, resource,
+ const struct rlimit64 __user *, new_rlim,
+ struct rlimit64 __user *, old_rlim)
+{
+ struct rlimit64 old64, new64;
+ struct rlimit old, new;
+ struct task_struct *tsk;
+ int ret;
+
+ if (new_rlim) {
+ if (copy_from_user(&new64, new_rlim, sizeof(new64)))
+ return -EFAULT;
+ rlim64_to_rlim(&new64, &new);
+ }
+
+ /* we don't want to fail after do_rlimit */
+ if (old_rlim && !access_ok(VERIFY_WRITE, old_rlim, sizeof(old64)))
+ return -EFAULT;
+
+ rcu_read_lock();
+ tsk = pid ? find_task_by_vpid(pid) : current;
+ if (!tsk) {
+ rcu_read_unlock();
+ return -ESRCH;
+ }
+ ret = check_prlimit_permission(tsk);
+ if (ret) {
+ rcu_read_unlock();
+ return ret;
+ }
+ get_task_struct(tsk);
+ rcu_read_unlock();
+
+ ret = do_prlimit(tsk, resource, new_rlim ? &new : NULL,
+ old_rlim ? &old : NULL);
+
+ if (!ret && old_rlim) {
+ rlim_to_rlim64(&old, &old64);
+ if (WARN_ON_ONCE(__copy_to_user(old_rlim, &old64,
+ sizeof(old64))))
+ ret = -EFAULT;
+ }
+
+ put_task_struct(tsk);
+ return ret;
+}
+
SYSCALL_DEFINE2(setrlimit, unsigned int, resource, struct rlimit __user *, rlim)
{
struct rlimit new_rlim;
--
1.7.1
--
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