From 0baf2a4dbf75abb7c186fd6c8d55d27aaa354a29 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Wed, 29 Oct 2014 14:50:35 -0700 Subject: kernel/kmod: fix use-after-free of the sub_info structure Found this in the message log on a s390 system: BUG kmalloc-192 (Not tainted): Poison overwritten Disabling lock debugging due to kernel taint INFO: 0x00000000684761f4-0x00000000684761f7. First byte 0xff instead of 0x6b INFO: Allocated in call_usermodehelper_setup+0x70/0x128 age=71 cpu=2 pid=648 __slab_alloc.isra.47.constprop.56+0x5f6/0x658 kmem_cache_alloc_trace+0x106/0x408 call_usermodehelper_setup+0x70/0x128 call_usermodehelper+0x62/0x90 cgroup_release_agent+0x178/0x1c0 process_one_work+0x36e/0x680 worker_thread+0x2f0/0x4f8 kthread+0x10a/0x120 kernel_thread_starter+0x6/0xc kernel_thread_starter+0x0/0xc INFO: Freed in call_usermodehelper_exec+0x110/0x1b8 age=71 cpu=2 pid=648 __slab_free+0x94/0x560 kfree+0x364/0x3e0 call_usermodehelper_exec+0x110/0x1b8 cgroup_release_agent+0x178/0x1c0 process_one_work+0x36e/0x680 worker_thread+0x2f0/0x4f8 kthread+0x10a/0x120 kernel_thread_starter+0x6/0xc kernel_thread_starter+0x0/0xc There is a use-after-free bug on the subprocess_info structure allocated by the user mode helper. In case do_execve() returns with an error ____call_usermodehelper() stores the error code to sub_info->retval, but sub_info can already have been freed. Regarding UMH_NO_WAIT, the sub_info structure can be freed by __call_usermodehelper() before the worker thread returns from do_execve(), allowing memory corruption when do_execve() failed after exec_mmap() is called. Regarding UMH_WAIT_EXEC, the call to umh_complete() allows call_usermodehelper_exec() to continue which then frees sub_info. To fix this race the code needs to make sure that the call to call_usermodehelper_freeinfo() is always done after the last store to sub_info->retval. Signed-off-by: Martin Schwidefsky Reviewed-by: Oleg Nesterov Cc: Tetsuo Handa Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kmod.c | 76 +++++++++++++++++++++++++++++------------------------------ 1 file changed, 37 insertions(+), 39 deletions(-) (limited to 'kernel') diff --git a/kernel/kmod.c b/kernel/kmod.c index 8637e041a247..80f7a6d00519 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -196,12 +196,34 @@ int __request_module(bool wait, const char *fmt, ...) EXPORT_SYMBOL(__request_module); #endif /* CONFIG_MODULES */ +static void call_usermodehelper_freeinfo(struct subprocess_info *info) +{ + if (info->cleanup) + (*info->cleanup)(info); + kfree(info); +} + +static void umh_complete(struct subprocess_info *sub_info) +{ + struct completion *comp = xchg(&sub_info->complete, NULL); + /* + * See call_usermodehelper_exec(). If xchg() returns NULL + * we own sub_info, the UMH_KILLABLE caller has gone away + * or the caller used UMH_NO_WAIT. + */ + if (comp) + complete(comp); + else + call_usermodehelper_freeinfo(sub_info); +} + /* * This is the task which runs the usermode application */ static int ____call_usermodehelper(void *data) { struct subprocess_info *sub_info = data; + int wait = sub_info->wait & ~UMH_KILLABLE; struct cred *new; int retval; @@ -221,7 +243,7 @@ static int ____call_usermodehelper(void *data) retval = -ENOMEM; new = prepare_kernel_cred(current); if (!new) - goto fail; + goto out; spin_lock(&umh_sysctl_lock); new->cap_bset = cap_intersect(usermodehelper_bset, new->cap_bset); @@ -233,7 +255,7 @@ static int ____call_usermodehelper(void *data) retval = sub_info->init(sub_info, new); if (retval) { abort_creds(new); - goto fail; + goto out; } } @@ -242,12 +264,13 @@ static int ____call_usermodehelper(void *data) retval = do_execve(getname_kernel(sub_info->path), (const char __user *const __user *)sub_info->argv, (const char __user *const __user *)sub_info->envp); +out: + sub_info->retval = retval; + /* wait_for_helper() will call umh_complete if UHM_WAIT_PROC. */ + if (wait != UMH_WAIT_PROC) + umh_complete(sub_info); if (!retval) return 0; - - /* Exec failed? */ -fail: - sub_info->retval = retval; do_exit(0); } @@ -258,26 +281,6 @@ static int call_helper(void *data) return ____call_usermodehelper(data); } -static void call_usermodehelper_freeinfo(struct subprocess_info *info) -{ - if (info->cleanup) - (*info->cleanup)(info); - kfree(info); -} - -static void umh_complete(struct subprocess_info *sub_info) -{ - struct completion *comp = xchg(&sub_info->complete, NULL); - /* - * See call_usermodehelper_exec(). If xchg() returns NULL - * we own sub_info, the UMH_KILLABLE caller has gone away. - */ - if (comp) - complete(comp); - else - call_usermodehelper_freeinfo(sub_info); -} - /* Keventd can't block, but this (a child) can. */ static int wait_for_helper(void *data) { @@ -336,18 +339,8 @@ static void __call_usermodehelper(struct work_struct *work) kmod_thread_locker = NULL; } - switch (wait) { - case UMH_NO_WAIT: - call_usermodehelper_freeinfo(sub_info); - break; - - case UMH_WAIT_PROC: - if (pid > 0) - break; - /* FALLTHROUGH */ - case UMH_WAIT_EXEC: - if (pid < 0) - sub_info->retval = pid; + if (pid < 0) { + sub_info->retval = pid; umh_complete(sub_info); } } @@ -588,7 +581,12 @@ int call_usermodehelper_exec(struct subprocess_info *sub_info, int wait) goto out; } - sub_info->complete = &done; + /* + * Set the completion pointer only if there is a waiter. + * This makes it possible to use umh_complete to free + * the data structure in case of UMH_NO_WAIT. + */ + sub_info->complete = (wait == UMH_NO_WAIT) ? NULL : &done; sub_info->wait = wait; queue_work(khelper_wq, &sub_info->work); -- cgit v1.2.3-59-g8ed1b