tracing: Fix bad use of igrab in trace_uprobe.c

As Miklos reported and suggested:

  This pattern repeats two times in trace_uprobe.c and in
  kernel/events/core.c as well:

      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
      if (ret)
          goto fail_address_parse;

      inode = igrab(d_inode(path.dentry));
      path_put(&path);

  And it's wrong.  You can only hold a reference to the inode if you
  have an active ref to the superblock as well (which is normally
  through path.mnt) or holding s_umount.

  This way unmounting the containing filesystem while the tracepoint is
  active will give you the "VFS: Busy inodes after unmount..." message
  and a crash when the inode is finally put.

  Solution: store path instead of inode.

This patch fixes two instances in trace_uprobe.c. struct path is added to
struct trace_uprobe to keep the inode and containing mount point
referenced.

Link: http://lkml.kernel.org/r/20180423172135.4050588-1-songliubraving@fb.com
Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Howard McLauchlan <hmclauchlan@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Miklos Szeredi <mszeredi@redhat.com>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 34fd0e0ec51d2a49c27d082f363be11276d7d753..ac892878dbe60d8f4ac527be8fc1f8d39a2958b9 100644 (file)
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -55,6 +55,7 @@ struct trace_uprobe {
        struct list_head                list;
        struct trace_uprobe_filter      filter;
        struct uprobe_consumer          consumer;
+       struct path                     path;
        struct inode                    *inode;
        char                            *filename;
        unsigned long                   offset;
@@ -289,7 +290,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
        for (i = 0; i < tu->tp.nr_args; i++)
                traceprobe_free_probe_arg(&tu->tp.args[i]);
 
-       iput(tu->inode);
+       path_put(&tu->path);
        kfree(tu->tp.call.class->system);
        kfree(tu->tp.call.name);
        kfree(tu->filename);
@@ -363,7 +364,6 @@ end:
 static int create_trace_uprobe(int argc, char **argv)
 {
        struct trace_uprobe *tu;
-       struct inode *inode;
        char *arg, *event, *group, *filename;
        char buf[MAX_EVENT_NAME_LEN];
        struct path path;
@@ -371,7 +371,6 @@ static int create_trace_uprobe(int argc, char **argv)
        bool is_delete, is_return;
        int i, ret;
 
-       inode = NULL;
        ret = 0;
        is_delete = false;
        is_return = false;
@@ -437,21 +436,16 @@ static int create_trace_uprobe(int argc, char **argv)
        }
        /* Find the last occurrence, in case the path contains ':' too. */
        arg = strrchr(argv[1], ':');
-       if (!arg) {
-               ret = -EINVAL;
-               goto fail_address_parse;
-       }
+       if (!arg)
+               return -EINVAL;
 
        *arg++ = '\0';
        filename = argv[1];
        ret = kern_path(filename, LOOKUP_FOLLOW, &path);
        if (ret)
-               goto fail_address_parse;
-
-       inode = igrab(d_real_inode(path.dentry));
-       path_put(&path);
+               return ret;
 
-       if (!inode || !S_ISREG(inode->i_mode)) {
+       if (!d_is_reg(path.dentry)) {
                ret = -EINVAL;
                goto fail_address_parse;
        }
@@ -490,7 +484,7 @@ static int create_trace_uprobe(int argc, char **argv)
                goto fail_address_parse;
        }
        tu->offset = offset;
-       tu->inode = inode;
+       tu->path = path;
        tu->filename = kstrdup(filename, GFP_KERNEL);
 
        if (!tu->filename) {
@@ -558,7 +552,7 @@ error:
        return ret;
 
 fail_address_parse:
-       iput(inode);
+       path_put(&path);
 
        pr_info("Failed to parse address or file.\n");
 
@@ -922,6 +916,7 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
                goto err_flags;
 
        tu->consumer.filter = filter;
+       tu->inode = d_real_inode(tu->path.dentry);
        ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
        if (ret)
                goto err_buffer;
@@ -967,6 +962,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
        WARN_ON(!uprobe_filter_is_empty(&tu->filter));
 
        uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
+       tu->inode = NULL;
        tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
 
        uprobe_buffer_disable();
@@ -1337,7 +1333,6 @@ struct trace_event_call *
 create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 {
        struct trace_uprobe *tu;
-       struct inode *inode;
        struct path path;
        int ret;
 
@@ -1345,11 +1340,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
        if (ret)
                return ERR_PTR(ret);
 
-       inode = igrab(d_inode(path.dentry));
-       path_put(&path);
-
-       if (!inode || !S_ISREG(inode->i_mode)) {
-               iput(inode);
+       if (!d_is_reg(path.dentry)) {
+               path_put(&path);
                return ERR_PTR(-EINVAL);
        }
 
@@ -1364,11 +1356,12 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
        if (IS_ERR(tu)) {
                pr_info("Failed to allocate trace_uprobe.(%d)\n",
                        (int)PTR_ERR(tu));
+               path_put(&path);
                return ERR_CAST(tu);
        }
 
        tu->offset = offs;
-       tu->inode = inode;
+       tu->path = path;
        tu->filename = kstrdup(name, GFP_KERNEL);
        init_trace_event_call(tu, &tu->tp.call);