On Fri, Aug 12, 2016 at 06:04:20PM -0400, robert.foss@xxxxxxxxxxxxx wrote:
> diff --git a/fs/proc/internal.h b/fs/proc/internal.h
> index aa27810..c55e1fe 100644
> --- a/fs/proc/internal.h
> +++ b/fs/proc/internal.h
> @@ -281,6 +281,7 @@ struct proc_maps_private {
> struct mm_struct *mm;
> #ifdef CONFIG_MMU
> struct vm_area_struct *tail_vma;
> + struct mem_size_stats *mss;
This is unused now, right?
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 4648c7f..b7612e9 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -246,6 +246,9 @@ static int proc_map_release(struct inode *inode, struct file *file)
> struct seq_file *seq = file->private_data;
> struct proc_maps_private *priv = seq->private;
>
> + if (!priv)
> + return 0;
> +
You might want to get rid of this, see below.
> +static int totmaps_open(struct inode *inode, struct file *file)
> +{
> + struct proc_maps_private *priv = NULL;
> + struct seq_file *seq;
> + int ret;
> +
> + ret = do_maps_open(inode, file, &proc_totmaps_op);
> + if (ret)
> + goto error;
[...]
> +error:
> + proc_map_release(inode, file);
> + return ret;
I don't think this is correct. Have a look at the other callers of
do_maps_open() - none of them do any cleanup steps on error, they
just return. I think the "goto error" here should be a return
instead.
Have a look at the error cases that can cause do_maps_open() to
fail: do_maps_open() just calls proc_maps_open(). If the
__seq_open_private() call fails because of memory pressure,
file->private_data is still NULL, and your newly added NULL check
in proc_map_release() causes proc_map_release() to be a no-op
there. But if proc_maps_open() fails later on, things get nasty:
If, for example, proc_mem_open() fails because of a ptrace
permission denial, __seq_open_file -> seq_open has already set
file->private_data to a struct seq_file *, and then
proc_maps_open(), prior to passing on the error code, calls
seq_release_private -> seq_release, which frees that
struct seq_file * without NULLing the private_data pointer.
As far as I can tell, proc_map_release() would then run into
a use-after-free scenario.
> + priv->task = get_proc_task(inode);
> + if (!priv->task) {
> + ret = -ESRCH;
> + goto error;
> + }
You're not actually using ->task anywhere in the current version,
right? Can this be deleted?
> +const struct file_operations proc_totmaps_operations = {
[...]
> + .release = proc_map_release,
This won't release priv->task, causing a memory leak (exploitable
through a reference counter overflow of the task_struct usage
counter).
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