From 12a3de0a965826096d8adc593bcf4392a7d5b459 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov Date: Wed, 30 Apr 2008 00:54:29 -0700 Subject: pids: sys_getpgid: fix unsafe *pid usage, s/tasklist/rcu/ 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 Cc: Roland McGrath Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sys.c | 36 +++++++++++++++++++++--------------- 1 file changed, 21 insertions(+), 15 deletions(-) (limited to 'kernel') diff --git a/kernel/sys.c b/kernel/sys.c index ddd28e261f3a..895d2d4c9493 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -991,31 +991,37 @@ 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 -- cgit v1.2.3