| Message ID | 1422223060-8561-1-git-send-email-richard@nod.at (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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). -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; }
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(+)