[PATCH] fs: check f_op before dereference its field

[PATCH] fs: check f_op before dereference its field

[Jiang Fang]

I don't know whether we can have NULL f_op today, but a quick
grep of '!file->f_op->' in fs directory shows most of times we
do the check. So fix the missing one.

Signed-off-by: Jiang Fang <jiang.xx.fang@gmail.com>
---
 fs/open.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/open.c b/fs/open.c
index 9b33c0c..192dd86 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -275,7 +275,7 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (((offset + len) > inode->i_sb->s_maxbytes) || ((offset + len) < 0))
 		return -EFBIG;
 
-	if (!file->f_op->fallocate)
+	if (!file->f_op || !file->f_op->fallocate)
 		return -EOPNOTSUPP;
 
 	sb_start_write(inode->i_sb);
-- 
1.7.9.5

Re: [PATCH] fs: check f_op before dereference its field

[Al Viro]

On Thu, Jan 24, 2013 at 10:53:20PM +0800, Jiang Fang wrote:
> I don't know whether we can have NULL f_op today, but a quick
> grep of '!file->f_op->' in fs directory shows most of times we
> do the check. So fix the missing one.

We should remove the bogus ones, actually, and hunt down the remaining
few places that set ->f_op to NULL (AFAICS, all of them in dvb and
in ->release() instances, at that; note that no methods can be ever
called after ->release(), so these assignments are pointless _and_
irrelevant for any call sites of the methods).