Extract have_task_perm() Various kernel function check if they are allowed to do something to another task. The ones that I have found are 1. The check for kill permissions 2. sys_migrate_pages() checking if a process is allowed to migrate the pages of another process. 3. sys_move_pages() checking if a process is allowed to migrate individual pages that are part of another process. Extract the common code in these checks to form a new function in kernel/signal.c have_task_perm(task, capability). The check is successful if 1. The current process has the indicated capability 2. The current effective userid is equal to the suid or uid of the target process. 3. The current userid is equal to the suid or uid of the target process. Note that there are similar checks for uid/gid/euid that are stored in a variety of structures in the kernel. Maybe those may also be extracted by a similar function that would not take a task parameter but an explicit specification of permission ids? ptrace() has a variation on the have_task_perm() check in may_attach(). ptrace checks for uid equal to euid, suid, uid or gid equal to egid sgid,gid. So one may not be able to kill a process explicyly but be able to ptrace() (and then PTRACE_KILL it) if one is a member of the same group? Weird. Plus ptrace does not support eid comparision. So explicit rights for ptracing cannot be set via the super user bit. Maybe we could consolidate all these checks and make them work in a coherent way? I dont think I am deep enough into this issue to takle that though. Signed-off-by: Christoph Lameter <clameter@xxxxxxx> Index: linux-2.6.17-rc4-mm3/mm/mempolicy.c =================================================================== --- linux-2.6.17-rc4-mm3.orig/mm/mempolicy.c 2006-05-22 18:03:32.283696770 -0700 +++ linux-2.6.17-rc4-mm3/mm/mempolicy.c 2006-05-23 08:55:24.371254745 -0700 @@ -926,15 +926,7 @@ asmlinkage long sys_migrate_pages(pid_t if (!mm) return -EINVAL; - /* - * Check if this process has the right to modify the specified - * process. The right exists if the process has administrative - * capabilities, superuser privileges or the same - * userid as the target process. - */ - if ((current->euid != task->suid) && (current->euid != task->uid) && - (current->uid != task->suid) && (current->uid != task->uid) && - !capable(CAP_SYS_NICE)) { + if (!have_task_perm(task, CAP_SYS_NICE)) { err = -EPERM; goto out; } Index: linux-2.6.17-rc4-mm3/mm/migrate.c =================================================================== --- linux-2.6.17-rc4-mm3.orig/mm/migrate.c 2006-05-22 18:03:32.286626275 -0700 +++ linux-2.6.17-rc4-mm3/mm/migrate.c 2006-05-23 08:55:24.372231247 -0700 @@ -781,15 +781,7 @@ asmlinkage long sys_move_pages(int pid, if (!mm) return -EINVAL; - /* - * Check if this process has the right to modify the specified - * process. The right exists if the process has administrative - * capabilities, superuser privileges or the same - * userid as the target process. - */ - if ((current->euid != task->suid) && (current->euid != task->uid) && - (current->uid != task->suid) && (current->uid != task->uid) && - !capable(CAP_SYS_NICE)) { + if (!have_task_perm(task, CAP_SYS_NICE)) { err = -EPERM; goto out2; } Index: linux-2.6.17-rc4-mm3/kernel/signal.c =================================================================== --- linux-2.6.17-rc4-mm3.orig/kernel/signal.c 2006-05-22 18:03:32.211435632 -0700 +++ linux-2.6.17-rc4-mm3/kernel/signal.c 2006-05-23 09:11:44.323266538 -0700 @@ -567,6 +567,25 @@ static int rm_from_queue(unsigned long m } /* + * Check if this process has the rights to do something + * with another process. + * + * The right exists if either + * 1. The current process has the indicated capability + * 2. The current effective user id is the user or superuser + * id of the other process. + * 3. The current user id is the user or superuser id of the other process. + */ +int have_task_perm(struct task_struct *t, int capability) +{ + if (capable(capability)) + return 1; + + return (current->euid == t->suid || current->euid == t->uid || + current->uid == t->suid || current->uid == t->uid); +} + +/* * Bad permissions for sending the signal */ static int check_kill_permission(int sig, struct siginfo *info, @@ -579,9 +598,7 @@ static int check_kill_permission(int sig if ((info == SEND_SIG_NOINFO || (!is_si_special(info) && SI_FROMUSER(info))) && ((sig != SIGCONT) || (current->signal->session != t->signal->session)) - && (current->euid ^ t->suid) && (current->euid ^ t->uid) - && (current->uid ^ t->suid) && (current->uid ^ t->uid) - && !capable(CAP_KILL)) + && !have_task_perm(t, CAP_KILL)) return error; error = security_task_kill(t, info, sig); Index: linux-2.6.17-rc4-mm3/include/linux/signal.h =================================================================== --- linux-2.6.17-rc4-mm3.orig/include/linux/signal.h 2006-05-22 18:03:31.841341429 -0700 +++ linux-2.6.17-rc4-mm3/include/linux/signal.h 2006-05-23 08:55:24.393714292 -0700 @@ -267,6 +267,8 @@ extern int sigprocmask(int, sigset_t *, struct pt_regs; extern int get_signal_to_deliver(siginfo_t *info, struct k_sigaction *return_ka, struct pt_regs *regs, void *cookie); +extern int have_task_perm(struct task_struct *, int); + #endif /* __KERNEL__ */ #endif /* _LINUX_SIGNAL_H */ - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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