Messages in this thread Patch in this message | | | Date | Mon, 24 Mar 2008 21:36:05 +0300 | From | Oleg Nesterov <> | Subject | [PATCH 2/2] pids: sys_getpgid: fix unsafe *pid usage, s/tasklist/rcu/ |
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1. sys_getpgid() needs rcu_read_lock() to derive the pgrp _nr, even if the task is current, otherwise we can race with another thread which does sys_setpgid().
2. Use rcu_read_lock() instead of tasklist_lock when pid != 0, make sure that we don't use the NULL pid if the task exits right after successful find_task_by_vpid().
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 25/kernel/sys.c~2_GETPGID 2008-03-24 21:09:19.000000000 +0300 +++ 25/kernel/sys.c 2008-03-24 21:14:43.000000000 +0300 @@ -985,31 +985,37 @@ out: asmlinkage long sys_getpgid(pid_t pid) { + struct task_struct *p; + struct pid *grp; + int retval; + + rcu_read_lock(); if (!pid) - return task_pgrp_vnr(current); + grp = task_pgrp(current); else { - int retval; - struct task_struct *p; - - read_lock(&tasklist_lock); - p = find_task_by_vpid(pid); retval = -ESRCH; - if (p) { - retval = security_task_getpgid(p); - if (!retval) - retval = task_pgrp_vnr(p); - } - read_unlock(&tasklist_lock); - return retval; + p = find_task_by_vpid(pid); + if (!p) + goto out; + grp = task_pgrp(p); + if (!grp) + goto out; + + retval = security_task_getpgid(p); + if (retval) + goto out; } + retval = pid_vnr(grp); +out: + rcu_read_unlock(); + return retval; } #ifdef __ARCH_WANT_SYS_GETPGRP asmlinkage long sys_getpgrp(void) { - /* SMP - assuming writes are word atomic this is fine */ - return task_pgrp_vnr(current); + return sys_getpgid(0); } #endif
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