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authorMichal Hocko <mhocko@suse.cz>2010-06-30 09:51:19 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-02 10:21:24 -0700
commit29540fc633e3f0ce474cf8d46806c0f92d1dd6f7 (patch)
parent05ae56ca1cd57e3b6fb57173e8f9e23f289880e9 (diff)
futex: futex_find_get_task remove credentails check
commit 7a0ea09ad5352efce8fe79ed853150449903b9f5 upstream. futex_find_get_task is currently used (through lookup_pi_state) from two contexts, futex_requeue and futex_lock_pi_atomic. None of the paths looks it needs the credentials check, though. Different (e)uids shouldn't matter at all because the only thing that is important for shared futex is the accessibility of the shared memory. The credentail check results in glibc assert failure or process hang (if glibc is compiled without assert support) for shared robust pthread mutex with priority inheritance if a process tries to lock already held lock owned by a process with a different euid: pthread_mutex_lock.c:312: __pthread_mutex_lock_full: Assertion `(-(e)) != 3 || !robust' failed. The problem is that futex_lock_pi_atomic which is called when we try to lock already held lock checks the current holder (tid is stored in the futex value) to get the PI state. It uses lookup_pi_state which in turn gets task struct from futex_find_get_task. ESRCH is returned either when the task is not found or if credentials check fails. futex_lock_pi_atomic simply returns if it gets ESRCH. glibc code, however, doesn't expect that robust lock returns with ESRCH because it should get either success or owner died. Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: Darren Hart <dvhltc@us.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Nick Piggin <npiggin@suse.de> Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
1 files changed, 4 insertions, 13 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 1ad4fa6db725..3071911eff5b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -429,20 +429,11 @@ static void free_pi_state(struct futex_pi_state *pi_state)
static struct task_struct * futex_find_get_task(pid_t pid)
struct task_struct *p;
- const struct cred *cred = current_cred(), *pcred;
p = find_task_by_vpid(pid);
- if (!p) {
- p = ERR_PTR(-ESRCH);
- } else {
- pcred = __task_cred(p);
- if (cred->euid != pcred->euid &&
- cred->euid != pcred->uid)
- p = ERR_PTR(-ESRCH);
- else
- get_task_struct(p);
- }
+ if (p)
+ get_task_struct(p);
@@ -564,8 +555,8 @@ lookup_pi_state(u32 uval, struct futex_hash_bucket *hb,
if (!pid)
return -ESRCH;
p = futex_find_get_task(pid);
- if (IS_ERR(p))
- return PTR_ERR(p);
+ if (!p)
+ return -ESRCH;
* We need to look at the task state flags to figure out,