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* [PATCH] fs: Detect API misuse of i_op->lookup
@ 2015-01-25 21:57 Richard Weinberger
  2015-01-25 22:16 ` Al Viro
  0 siblings, 1 reply; 3+ messages in thread
From: Richard Weinberger @ 2015-01-25 21:57 UTC (permalink / raw)
  To: viro; +Cc: linux-fsdevel, linux-kernel, Richard Weinberger

Hunting down a refcount issue in an out-of-tree filesystem uncovered
that its lookup function directly returned the dentry which was passed to it.
Add a BUG_ON() to detect such misuse in future.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
 fs/namei.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/namei.c b/fs/namei.c
index bc35b02..f8ccae6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1370,6 +1370,7 @@ static struct dentry *lookup_real(struct inode *dir, struct dentry *dentry,
 
 	old = dir->i_op->lookup(dir, dentry, flags);
 	if (unlikely(old)) {
+		BUG_ON(old == dentry);
 		dput(dentry);
 		dentry = old;
 	}
-- 
2.2.2


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] fs: Detect API misuse of i_op->lookup
  2015-01-25 21:57 [PATCH] fs: Detect API misuse of i_op->lookup Richard Weinberger
@ 2015-01-25 22:16 ` Al Viro
  2015-01-25 22:20   ` Richard Weinberger
  0 siblings, 1 reply; 3+ messages in thread
From: Al Viro @ 2015-01-25 22:16 UTC (permalink / raw)
  To: Richard Weinberger; +Cc: linux-fsdevel, linux-kernel

On Sun, Jan 25, 2015 at 10:57:40PM +0100, Richard Weinberger wrote:
> Hunting down a refcount issue in an out-of-tree filesystem uncovered
> that its lookup function directly returned the dentry which was passed to it.
> Add a BUG_ON() to detect such misuse in future.

In principle, it's not a bug.  You *must* grab a reference to dentry before
returning it, but you can very well decide to return the one you've got -
any place where have ->lookup() return NULL has every right to become
return dget(dentry).

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] fs: Detect API misuse of i_op->lookup
  2015-01-25 22:16 ` Al Viro
@ 2015-01-25 22:20   ` Richard Weinberger
  0 siblings, 0 replies; 3+ messages in thread
From: Richard Weinberger @ 2015-01-25 22:20 UTC (permalink / raw)
  To: Al Viro; +Cc: linux-fsdevel, linux-kernel

Am 25.01.2015 um 23:16 schrieb Al Viro:
> On Sun, Jan 25, 2015 at 10:57:40PM +0100, Richard Weinberger wrote:
>> Hunting down a refcount issue in an out-of-tree filesystem uncovered
>> that its lookup function directly returned the dentry which was passed to it.
>> Add a BUG_ON() to detect such misuse in future.
> 
> In principle, it's not a bug.  You *must* grab a reference to dentry before
> returning it, but you can very well decide to return the one you've got -
> any place where have ->lookup() return NULL has every right to become
> return dget(dentry).

Thanks for the clarification! The filesystem in question did of course
not grab a reference before returning the same dentry.

Thanks,
//richard

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2015-01-25 22:20 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2015-01-25 21:57 [PATCH] fs: Detect API misuse of i_op->lookup Richard Weinberger
2015-01-25 22:16 ` Al Viro
2015-01-25 22:20   ` Richard Weinberger

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