projects/linux·commit 36048853

debugfs: fix race in u32_array_read and allocate array at open

36048853 · David Rientjes <[email protected]> · 2012-09-21 02:16:29 -07:00

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.

Note that because the file has always been non-seekable, you can't open
it and read it multiple times anyway, so the data has always been
generated just once.  The difference is that now it is generated at open
time rather than at the time of the first read, and that avoids the
race.

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]>
Signed-off-by: Linus Torvalds <[email protected]>
Commit
36048853c5257a7b6df346b83758ffa776a59e9f
Parents
c46de226

Changes

1 files changed · +11 −22

FileStatusAddDelContent
fs/debugfs/file.cmodified+11−22View file

fs/debugfs/file.c

View file
diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 2340f69..a09d3c0 100644
--- 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);