From: "Steven Rostedt (Google)" rostedt@goodmis.org
stable inclusion from stable-v5.10.202 commit 1e61436b331720946e60be3c5f9cf6f3e8d07b93 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I90MN1
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
--------------------------------
commit bb32500fb9b78215e4ef6ee8b4345c5f5d7eafb4 upstream.
The following can crash the kernel:
# cd /sys/kernel/tracing # echo 'p:sched schedule' > kprobe_events # exec 5>>events/kprobes/sched/enable # > kprobe_events # exec 5>&-
The above commands:
1. Change directory to the tracefs directory 2. Create a kprobe event (doesn't matter what one) 3. Open bash file descriptor 5 on the enable file of the kprobe event 4. Delete the kprobe event (removes the files too) 5. Close the bash file descriptor 5
The above causes a crash!
BUG: kernel NULL pointer dereference, address: 0000000000000028 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI CPU: 6 PID: 877 Comm: bash Not tainted 6.5.0-rc4-test-00008-g2c6b6b1029d4-dirty #186 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 RIP: 0010:tracing_release_file_tr+0xc/0x50
What happens here is that the kprobe event creates a trace_event_file "file" descriptor that represents the file in tracefs to the event. It maintains state of the event (is it enabled for the given instance?). Opening the "enable" file gets a reference to the event "file" descriptor via the open file descriptor. When the kprobe event is deleted, the file is also deleted from the tracefs system which also frees the event "file" descriptor.
But as the tracefs file is still opened by user space, it will not be totally removed until the final dput() is called on it. But this is not true with the event "file" descriptor that is already freed. If the user does a write to or simply closes the file descriptor it will reference the event "file" descriptor that was just freed, causing a use-after-free bug.
To solve this, add a ref count to the event "file" descriptor as well as a new flag called "FREED". The "file" will not be freed until the last reference is released. But the FREE flag will be set when the event is removed to prevent any more modifications to that event from happening, even if there's still a reference to the event "file" descriptor.
Link: https://lore.kernel.org/linux-trace-kernel/20231031000031.1e705592@gandalf.l... Link: https://lore.kernel.org/linux-trace-kernel/20231031122453.7a48b923@gandalf.l...
Cc: stable@vger.kernel.org Cc: Mark Rutland mark.rutland@arm.com Fixes: f5ca233e2e66d ("tracing: Increase trace array ref count on enable and filter files") Reported-by: Beau Belgrave beaub@linux.microsoft.com Tested-by: Beau Belgrave beaub@linux.microsoft.com Reviewed-by: Masami Hiramatsu (Google) mhiramat@kernel.org Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Yang Jihong yangjihong1@huawei.com Signed-off-by: Zheng Yejian zhengyejian1@huawei.com --- include/linux/trace_events.h | 4 +++ kernel/trace/trace.c | 15 +++++++++++ kernel/trace/trace.h | 3 +++ kernel/trace/trace_events.c | 43 +++++++++++++++++++----------- kernel/trace/trace_events_filter.c | 3 +++ 5 files changed, 53 insertions(+), 15 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 409385b25ecb..e100efa2536e 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -376,6 +376,7 @@ enum { EVENT_FILE_FL_TRIGGER_COND_BIT, EVENT_FILE_FL_PID_FILTER_BIT, EVENT_FILE_FL_WAS_ENABLED_BIT, + EVENT_FILE_FL_FREED_BIT, };
extern struct trace_event_file *trace_get_event_file(const char *instance, @@ -514,6 +515,7 @@ extern int __kprobe_event_add_fields(struct dynevent_cmd *cmd, ...); * TRIGGER_COND - When set, one or more triggers has an associated filter * PID_FILTER - When set, the event is filtered based on pid * WAS_ENABLED - Set when enabled to know to clear trace on module removal + * FREED - File descriptor is freed, all fields should be considered invalid */ enum { EVENT_FILE_FL_ENABLED = (1 << EVENT_FILE_FL_ENABLED_BIT), @@ -527,6 +529,7 @@ enum { EVENT_FILE_FL_TRIGGER_COND = (1 << EVENT_FILE_FL_TRIGGER_COND_BIT), EVENT_FILE_FL_PID_FILTER = (1 << EVENT_FILE_FL_PID_FILTER_BIT), EVENT_FILE_FL_WAS_ENABLED = (1 << EVENT_FILE_FL_WAS_ENABLED_BIT), + EVENT_FILE_FL_FREED = (1 << EVENT_FILE_FL_FREED_BIT), };
struct trace_event_file { @@ -555,6 +558,7 @@ struct trace_event_file { * caching and such. Which is mostly OK ;-) */ unsigned long flags; + atomic_t ref; /* ref count for opened files */ atomic_t sm_ref; /* soft-mode reference counter */ atomic_t tm_ref; /* trigger-mode reference counter */ }; diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 0ff149b94430..b4898c8c32e5 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -4526,6 +4526,20 @@ int tracing_open_file_tr(struct inode *inode, struct file *filp) if (ret) return ret;
+ mutex_lock(&event_mutex); + + /* Fail if the file is marked for removal */ + if (file->flags & EVENT_FILE_FL_FREED) { + trace_array_put(file->tr); + ret = -ENODEV; + } else { + event_file_get(file); + } + + mutex_unlock(&event_mutex); + if (ret) + return ret; + filp->private_data = inode->i_private;
return 0; @@ -4536,6 +4550,7 @@ int tracing_release_file_tr(struct inode *inode, struct file *filp) struct trace_event_file *file = inode->i_private;
trace_array_put(file->tr); + event_file_put(file);
return 0; } diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h index d5d9cdb5551f..68e8c91cda79 100644 --- a/kernel/trace/trace.h +++ b/kernel/trace/trace.h @@ -1782,6 +1782,9 @@ extern int register_event_command(struct event_command *cmd); extern int unregister_event_command(struct event_command *cmd); extern int register_trigger_hist_enable_disable_cmds(void);
+extern void event_file_get(struct trace_event_file *file); +extern void event_file_put(struct trace_event_file *file); + /** * struct event_trigger_ops - callbacks for trace event triggers * diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 605890e20018..6bd2c5d8b5ac 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -743,26 +743,38 @@ static void remove_subsystem(struct trace_subsystem_dir *dir) } }
-static void remove_event_file_dir(struct trace_event_file *file) +void event_file_get(struct trace_event_file *file) { - struct dentry *dir = file->dir; - struct dentry *child; + atomic_inc(&file->ref); +}
- if (dir) { - spin_lock(&dir->d_lock); /* probably unneeded */ - list_for_each_entry(child, &dir->d_subdirs, d_child) { - if (d_really_is_positive(child)) /* probably unneeded */ - d_inode(child)->i_private = NULL; - } - spin_unlock(&dir->d_lock); +void event_file_put(struct trace_event_file *file) +{ + if (WARN_ON_ONCE(!atomic_read(&file->ref))) { + if (file->flags & EVENT_FILE_FL_FREED) + kmem_cache_free(file_cachep, file); + return; + }
- tracefs_remove(dir); + if (atomic_dec_and_test(&file->ref)) { + /* Count should only go to zero when it is freed */ + if (WARN_ON_ONCE(!(file->flags & EVENT_FILE_FL_FREED))) + return; + kmem_cache_free(file_cachep, file); } +} + +static void remove_event_file_dir(struct trace_event_file *file) +{ + struct dentry *dir = file->dir; + + tracefs_remove(dir);
list_del(&file->list); remove_subsystem(file->system); free_event_filter(file->filter); - kmem_cache_free(file_cachep, file); + file->flags |= EVENT_FILE_FL_FREED; + event_file_put(file); }
/* @@ -1135,7 +1147,7 @@ event_enable_read(struct file *filp, char __user *ubuf, size_t cnt, flags = file->flags; mutex_unlock(&event_mutex);
- if (!file) + if (!file || flags & EVENT_FILE_FL_FREED) return -ENODEV;
if (flags & EVENT_FILE_FL_ENABLED && @@ -1173,7 +1185,7 @@ event_enable_write(struct file *filp, const char __user *ubuf, size_t cnt, ret = -ENODEV; mutex_lock(&event_mutex); file = event_file_data(filp); - if (likely(file)) + if (likely(file && !(file->flags & EVENT_FILE_FL_FREED))) ret = ftrace_event_enable_disable(file, val); mutex_unlock(&event_mutex); break; @@ -1442,7 +1454,7 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
mutex_lock(&event_mutex); file = event_file_data(filp); - if (file) + if (file && !(file->flags & EVENT_FILE_FL_FREED)) print_event_filter(file, s); mutex_unlock(&event_mutex);
@@ -2478,6 +2490,7 @@ trace_create_new_event(struct trace_event_call *call, atomic_set(&file->tm_ref, 0); INIT_LIST_HEAD(&file->triggers); list_add(&file->list, &tr->events); + event_file_get(file);
return file; } diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index a255ffbe342f..c1db5b62d811 100644 --- a/kernel/trace/trace_events_filter.c +++ b/kernel/trace/trace_events_filter.c @@ -1893,6 +1893,9 @@ int apply_event_filter(struct trace_event_file *file, char *filter_string) struct event_filter *filter = NULL; int err;
+ if (file->flags & EVENT_FILE_FL_FREED) + return -ENODEV; + if (!strcmp(strstrip(filter_string), "0")) { filter_disable(file); filter = event_filter(file);