u32_array_open() is racy when multiple threads read from a file with a
seek position of zero, i.e. when two or more simultaneous reads are
occurring after the non-seekable files are created. It is possible that
file->private_data is double-freed because the threads races between
kfree(file->private-data);
and
file->private_data = NULL;
The fix is to only do format_array_alloc() when the file is opened and
free it when it is closed. This means that any thread that holds the
file open and reads multiple times will see persistent data; they must
close() and open() the file again to see new data, like a simple cat of
the file.
Reported-by: Dave Jones <[email protected]>
Acked-by: Konrad Rzeszutek Wilk <[email protected]>
Tested-by: Raghavendra <[email protected]>
Signed-off-by: David Rientjes <[email protected]>
---
fs/debugfs/file.c | 33 +++++++++++----------------------
1 file changed, 11 insertions(+), 22 deletions(-)
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -526,12 +526,6 @@ struct array_data {
u32 elements;
};
-static int u32_array_open(struct inode *inode, struct file *file)
-{
- file->private_data = NULL;
- return nonseekable_open(inode, file);
-}
-
static size_t format_array(char *buf, size_t bufsize, const char *fmt,
u32 *array, u32 array_size)
{
@@ -573,26 +567,21 @@ static char *format_array_alloc(const char *fmt, u32
*array,
return ret;
}
-static ssize_t u32_array_read(struct file *file, char __user *buf, size_t len,
- loff_t *ppos)
+static int u32_array_open(struct inode *inode, struct file *file)
{
- struct inode *inode = file->f_path.dentry->d_inode;
struct array_data *data = inode->i_private;
- size_t size;
- if (*ppos == 0) {
- if (file->private_data) {
- kfree(file->private_data);
- file->private_data = NULL;
- }
-
- file->private_data = format_array_alloc("%u", data->array,
- data->elements);
- }
+ file->private_data = format_array_alloc("%u", data->array,
+ data->elements);
+ if (!file->private_data)
+ return -ENOMEM;
+ return nonseekable_open(inode, file);
+}
- size = 0;
- if (file->private_data)
- size = strlen(file->private_data);
+static ssize_t u32_array_read(struct file *file, char __user *buf, size_t len,
+ loff_t *ppos)
+{
+ size_t size = strlen(file->private_data);
return simple_read_from_buffer(buf, len, ppos,
file->private_data, size);
--
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