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    Subject[PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c
    Date
    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.

    Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
    Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
    Cc: Steven Rostedt <rostedt@goodmis.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>
    Reported-by: Miklos Szeredi <miklos@szeredi.hu>
    Signed-off-by: Song Liu <songliubraving@fb.com>
    ---
    kernel/trace/trace_uprobe.c | 42 ++++++++++++++----------------------------
    1 file changed, 14 insertions(+), 28 deletions(-)

    diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
    index 0d450b4..80dfcdf 100644
    --- a/kernel/trace/trace_uprobe.c
    +++ b/kernel/trace/trace_uprobe.c
    @@ -55,7 +55,7 @@ struct trace_uprobe {
    struct list_head list;
    struct trace_uprobe_filter filter;
    struct uprobe_consumer consumer;
    - struct inode *inode;
    + struct path path;
    char *filename;
    unsigned long offset;
    unsigned long nhit;
    @@ -289,7 +289,7 @@ 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 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
    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 +370,6 @@ 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;
    @@ -448,14 +446,6 @@ static int create_trace_uprobe(int argc, char **argv)
    if (ret)
    goto fail_address_parse;

    - inode = igrab(d_inode(path.dentry));
    - path_put(&path);
    -
    - if (!inode || !S_ISREG(inode->i_mode)) {
    - ret = -EINVAL;
    - goto fail_address_parse;
    - }
    -
    ret = kstrtoul(arg, 0, &offset);
    if (ret)
    goto fail_address_parse;
    @@ -490,7 +480,8 @@ static int create_trace_uprobe(int argc, char **argv)
    goto fail_address_parse;
    }
    tu->offset = offset;
    - tu->inode = inode;
    + tu->path.mnt = path.mnt;
    + tu->path.dentry = path.dentry;
    tu->filename = kstrdup(filename, GFP_KERNEL);

    if (!tu->filename) {
    @@ -558,7 +549,7 @@ static int create_trace_uprobe(int argc, char **argv)
    return ret;

    fail_address_parse:
    - iput(inode);
    + path_put(&path);

    pr_info("Failed to parse address or file.\n");

    @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
    goto err_flags;

    tu->consumer.filter = filter;
    - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
    + ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
    + &tu->consumer);
    if (ret)
    goto err_buffer;

    @@ -981,7 +973,7 @@ 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);
    + uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
    tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;

    uprobe_buffer_disable();
    @@ -1056,7 +1048,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
    write_unlock(&tu->filter.rwlock);

    if (!done)
    - return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
    + return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
    + &tu->consumer, false);

    return 0;
    }
    @@ -1088,7 +1081,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)

    err = 0;
    if (!done) {
    - err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
    + err = uprobe_apply(d_inode(tu->path.dentry),
    + tu->offset, &tu->consumer, true);
    if (err)
    uprobe_perf_close(tu, event);
    }
    @@ -1352,7 +1346,6 @@ 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;

    @@ -1360,14 +1353,6 @@ 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);
    - return ERR_PTR(-EINVAL);
    - }
    -
    /*
    * local trace_kprobes are not added to probe_list, so they are never
    * searched in find_trace_kprobe(). Therefore, there is no concern of
    @@ -1383,7 +1368,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
    }

    tu->offset = offs;
    - tu->inode = inode;
    + tu->path.mnt = path.mnt;
    + tu->path.dentry = path.dentry;
    tu->filename = kstrdup(name, GFP_KERNEL);
    init_trace_event_call(tu, &tu->tp.call);

    --
    2.9.5
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