Re: [PATCH] FS: Fixed buffer overflow issue in seq_read()

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, 19 Nov 2013, Al Viro wrote:
> 
> seq_file: always clear m->count when we free m->buf

Ok, applied.

What do you think about then just abstracing out that now common sequence 
of re-allocating a larger buffer, while clearing m->count?

IOW, something like the appended..

              Linus

---
 fs/seq_file.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index 1d641bb108d2..f513e1efa49d 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -82,6 +82,14 @@ int seq_open(struct file *file, const struct seq_operations *op)
 }
 EXPORT_SYMBOL(seq_open);
 
+static int grow_seq_buf(struct seq_file *m)
+{
+	kfree(m->buf);
+	m->count = 0;
+	m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
+	return m->buf != NULL;
+}
+
 static int traverse(struct seq_file *m, loff_t offset)
 {
 	loff_t pos = 0, index;
@@ -135,10 +143,7 @@ static int traverse(struct seq_file *m, loff_t offset)
 
 Eoverflow:
 	m->op->stop(m, p);
-	kfree(m->buf);
-	m->count = 0;
-	m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
-	return !m->buf ? -ENOMEM : -EAGAIN;
+	return grow_seq_buf(m) ? -EAGAIN : -ENOMEM;
 }
 
 /**
@@ -232,10 +237,7 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
 		if (m->count < m->size)
 			goto Fill;
 		m->op->stop(m, p);
-		kfree(m->buf);
-		m->count = 0;
-		m->buf = kmalloc(m->size <<= 1, GFP_KERNEL);
-		if (!m->buf)
+		if (!grow_seq_buf(m))
 			goto Enomem;
 		m->version = 0;
 		pos = m->index;