| Message ID | 20200817115933.44565-1-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/migrate: Avoid possible unnecessary ptrace_may_access() call in kernel_move_pages() | expand |
On Mon, Aug 17, 2020 at 07:59:33AM -0400, Miaohe Lin wrote: > There is no need to check if this process has the right to modify the > specified process when they are same. We should probably also skip the security hook call if a process is modifying its own pages. How about this instead? diff --git a/mm/migrate.c b/mm/migrate.c index f37729673558..84dc1f42161d 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1797,33 +1797,22 @@ static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages, return nr_pages ? -EFAULT : 0; } -/* - * Move a list of pages in the address space of the currently executing - * process. - */ -static int kernel_move_pages(pid_t pid, unsigned long nr_pages, - const void __user * __user *pages, - const int __user *nodes, - int __user *status, int flags) +static struct mm_struct *find_mm_struct(pid_t pid, nodemask_t *mem_nodes) { struct task_struct *task; struct mm_struct *mm; - int err; - nodemask_t task_nodes; - - /* Check flags */ - if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL)) - return -EINVAL; - if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE)) - return -EPERM; + if (!pid) { + mmget(current->mm); + *mem_nodes = cpuset_mems_allowed(current); + return current->mm; + } - /* Find the mm_struct */ rcu_read_lock(); - task = pid ? find_task_by_vpid(pid) : current; + task = find_task_by_vpid(pid); if (!task) { rcu_read_unlock(); - return -ESRCH; + return ERR_PTR(-ESRCH); } get_task_struct(task); @@ -1833,22 +1822,49 @@ static int kernel_move_pages(pid_t pid, unsigned long nr_pages, */ if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { rcu_read_unlock(); - err = -EPERM; + mm = ERR_PTR(-EPERM); goto out; } rcu_read_unlock(); - err = security_task_movememory(task); - if (err) + mm = ERR_PTR(security_task_movememory(task)); + if (IS_ERR(mm)) goto out; - task_nodes = cpuset_mems_allowed(task); + *mem_nodes = cpuset_mems_allowed(task); mm = get_task_mm(task); +out: put_task_struct(task); if (!mm) + mm = ERR_PTR(-EINVAL); + return mm; +} + +/* + * Move a list of pages in the address space of the specified + * process (pid of 0 means current). + */ +static int kernel_move_pages(pid_t pid, unsigned long nr_pages, + const void __user * __user *pages, + const int __user *nodes, + int __user *status, int flags) +{ + struct mm_struct *mm; + int err; + nodemask_t task_nodes; + + /* Check flags */ + if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL)) return -EINVAL; + if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE)) + return -EPERM; + + mm = find_mm_struct(pid, &task_nodes); + if (IS_ERR(mm)) + return PTR_ERR(mm); + if (nodes) err = do_pages_move(mm, task_nodes, nr_pages, pages, nodes, status, flags); @@ -1857,10 +1873,6 @@ static int kernel_move_pages(pid_t pid, unsigned long nr_pages, mmput(mm); return err; - -out: - put_task_struct(task); - return err; } SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
On Mon, Aug 17, 2020 at 07:59:33AM -0400, Miaohe Lin wrote: > There is no need to check if this process has the right to modify the > specified process when they are same. > > Signed-off-by: Hongxiang Lou <louhongxiang@huawei.com> > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/migrate.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 34a842a8eb6a..342c1ce0b433 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1903,7 +1903,7 @@ static int kernel_move_pages(pid_t pid, unsigned long nr_pages, > * Check if this process has the right to modify the specified > * process. Use the regular "ptrace_may_access()" checks. > */ > - if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > + if (pid && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { > rcu_read_unlock(); > err = -EPERM; > goto out; NAK, please don't do this -- the ptrace and security hooks already do these kinds of self-introspection checks, and I'd like to keep a central place to perform these kinds of checks. Is there a specific problem you've encountered that this fixes?
diff --git a/mm/migrate.c b/mm/migrate.c index 34a842a8eb6a..342c1ce0b433 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1903,7 +1903,7 @@ static int kernel_move_pages(pid_t pid, unsigned long nr_pages, * Check if this process has the right to modify the specified * process. Use the regular "ptrace_may_access()" checks. */ - if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { + if (pid && !ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) { rcu_read_unlock(); err = -EPERM; goto out;