[PATCH] fuse: Initialize the flock flag in the fuse_file structure upon allocation

[PATCH] fuse: Initialize the flock flag in the fuse_file structure upon allocation

[Mateusz Jurczyk]

Add initialization of the flock flag in the fuse_file structure after it
is allocated.

Before the patch, the flock flag could remain uninitialized for the
lifespan of the fuse_file allocation: it was not pre-set by kmalloc() or
later in the fuse_file_alloc() function. Unless set to true in
fuse_file_flock(), it would remain in an indeterminate state until
read in an if statement in fuse_release_common(). This could consequently
lead to taking an unexpected branch in the code.

The bug was discovered by a runtime instrumentation designed to detect use
of uninitialized memory in the kernel.

Signed-off-by: Mateusz Jurczyk <mjurczyk@google.com>
---
 fs/fuse/file.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 3ee4fdc3da9e..c9a86a748ceb 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -66,6 +66,8 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
 	ff->kh = ++fc->khctr;
 	spin_unlock(&fc->lock);
 
+	ff->flock = false;
+
 	return ff;
 }
 
-- 
2.13.1.508.gb3defc5cc-goog

Re: [PATCH] fuse: Initialize the flock flag in the fuse_file structure upon allocation

[Miklos Szeredi]

On Wed, Jun 7, 2017 at 12:26 PM, Mateusz Jurczyk <mjurczyk@google.com> wrote:
> Add initialization of the flock flag in the fuse_file structure after it
> is allocated.
>
> Before the patch, the flock flag could remain uninitialized for the
> lifespan of the fuse_file allocation: it was not pre-set by kmalloc() or
> later in the fuse_file_alloc() function. Unless set to true in
> fuse_file_flock(), it would remain in an indeterminate state until
> read in an if statement in fuse_release_common(). This could consequently
> lead to taking an unexpected branch in the code.
>
> The bug was discovered by a runtime instrumentation designed to detect use
> of uninitialized memory in the kernel.
>
> Signed-off-by: Mateusz Jurczyk <mjurczyk@google.com>

Thanks for spotting this.   Pushed a modified version (kzalloc instead
of explicit init) to the fuse git tree.

Thanks,
Miklos

> ---
>  fs/fuse/file.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 3ee4fdc3da9e..c9a86a748ceb 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -66,6 +66,8 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
>         ff->kh = ++fc->khctr;
>         spin_unlock(&fc->lock);
>
> +       ff->flock = false;
> +
>         return ff;
>  }
>
> --
> 2.13.1.508.gb3defc5cc-goog
>