From 1447399b3e34af016c368b4178db7ef0e04e15b0 Mon Sep 17 00:00:00 2001 From: Daniel J Blueman Date: Tue, 9 Nov 2010 21:33:02 +0100 Subject: ioprio: fix RCU locking around task dereference With 2.6.37-rc1, I observe sys_ioprio_set not taking the RCU lock [1] across access to the task credentials. Inspecting the code in fs/ioprio.c, the tasklist_lock is held for read across the __task_cred call, which is presumably sufficient to prevent the task credentials becoming stale. =================================================== [ INFO: suspicious rcu_dereference_check() usage. ] --------------------------------------------------- kernel/pid.c:419 invoked rcu_dereference_check() without protection! other info that might help us debug this: rcu_scheduler_active = 1, debug_locks = 1 1 lock held by start-stop-daem/2246: #0: (tasklist_lock){.?.?..}, at: [] sys_ioprio_set+0x8a/0x400 stack backtrace: Pid: 2246, comm: start-stop-daem Not tainted 2.6.37-rc1-330cd+ #2 Call Trace: [] lockdep_rcu_dereference+0xa4/0xc0 [] find_task_by_pid_ns+0x81/0x90 [] find_task_by_vpid+0x1d/0x20 [] sys_ioprio_set+0x3f0/0x400 [] ? trace_hardirqs_on_thunk+0x3a/0x3f [] system_call_fastpath+0x16/0x1b Take the RCU lock for read across acquiring the pointer to the task credentials and dereferencing it. Signed-off-by: Daniel J Blueman Fixed up by Jens to fix missing rcu_read_unlock() on mismatches. Signed-off-by: Jens Axboe --- fs/ioprio.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) (limited to 'fs/ioprio.c') diff --git a/fs/ioprio.c b/fs/ioprio.c index 748cfb92dcc6..8def14e24c37 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -139,7 +139,12 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) break; do_each_thread(g, p) { - if (__task_cred(p)->uid != who) + int match; + + rcu_read_lock(); + match = __task_cred(p)->uid == who; + rcu_read_unlock(); + if (!match) continue; ret = set_task_ioprio(p, ioprio); if (ret) @@ -232,7 +237,12 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) break; do_each_thread(g, p) { - if (__task_cred(p)->uid != user->uid) + int match; + + rcu_read_lock(); + match = __task_cred(p)->uid == user->uid; + rcu_read_unlock(); + if (!match) continue; tmpio = get_task_ioprio(p); if (tmpio < 0) -- cgit v1.2.1 From f85acd81aa623e3dcf268c90e5cd8ecf36830984 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Tue, 9 Nov 2010 21:26:56 +0100 Subject: ioprio: rcu_read_lock/unlock protect find_task_by_vpid call (V2) Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns= Assertion failed in sys_ioprio_get. The patch is fixing assertion failure in ioprio_set as well. kernel/pid.c:419 invoked rcu_dereference_check() without protection! stack backtrace: Pid: 4254, comm: iotop Not tainted Call Trace: [] lockdep_rcu_dereference+0xaa/0xb2 [] find_task_by_pid_ns+0x4f/0x68 [] find_task_by_vpid+0x1d/0x1f [] sys_ioprio_get+0x50/0x2da [] system_call_fastpath+0x16/0x1b V2: rcu critical section expanded according to comment by Paul E. McKenney Signed-off-by: Sergey Senozhatsky Acked-by: Paul E. McKenney Signed-off-by: Jens Axboe --- fs/ioprio.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'fs/ioprio.c') diff --git a/fs/ioprio.c b/fs/ioprio.c index 8def14e24c37..2f7d05c89922 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -111,12 +111,14 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio) read_lock(&tasklist_lock); switch (which) { case IOPRIO_WHO_PROCESS: + rcu_read_lock(); if (!who) p = current; else p = find_task_by_vpid(who); if (p) ret = set_task_ioprio(p, ioprio); + rcu_read_unlock(); break; case IOPRIO_WHO_PGRP: if (!who) @@ -205,12 +207,14 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) read_lock(&tasklist_lock); switch (which) { case IOPRIO_WHO_PROCESS: + rcu_read_lock(); if (!who) p = current; else p = find_task_by_vpid(who); if (p) ret = get_task_ioprio(p); + rcu_read_unlock(); break; case IOPRIO_WHO_PGRP: if (!who) -- cgit v1.2.1