On Thu, Jan 21, 2021 at 4:43 AM Icenowy Zheng icenowy@aosc.io wrote:
在 2021-01-20星期三的 11:20 +0100，Miklos Szeredi写道：
On Tue, Jan 05, 2021 at 08:47:41AM +0200, Amir Goldstein wrote:
On Tue, Jan 5, 2021 at 2:36 AM Icenowy Zheng icenowy@aosc.io wrote:
The function ovl_dir_real_file() currently uses the semaphore of the inode to synchronize write to the upperfile cache field.
Although the inode lock is a rw_sem it is referred to as the "inode lock" and you also left semaphore in the commit subject. No need to re-post. This can be fixed on commit.
However, this function will get called by ovl_ioctl_set_flags(), which utilizes the inode semaphore too. In this case ovl_dir_real_file() will try to claim a lock that is owned by a function in its call stack, which won't get released before ovl_dir_real_file() returns.
Define a dedicated semaphore for the upperfile cache, so that the deadlock won't happen.
Fixes: 61536bed2149 ("ovl: support [S|G]ETFLAGS and FS[S|G]ETXATTR ioctls for directories") Cc: stable@vger.kernel.org # v5.10 Signed-off-by: Icenowy Zheng icenowy@aosc.io
Changes in v2:
- Fixed missing replacement in error handling path.
Changes in v3:
- Use mutex instead of semaphore.
fs/overlayfs/readdir.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index 01620ebae1bd..3980f9982f34 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -56,6 +56,7 @@ struct ovl_dir_file { struct list_head *cursor; struct file *realfile; struct file *upperfile;
struct mutex upperfile_mutex;That's a very specific name. This mutex protects members of struct ovl_dir_file, which could evolve into struct ovl_file one day (because no reason to cache only dir upper file), so I would go with a more generic name, but let's leave it to Miklos to decide.
He could have a different idea altogether for fixing this bug.
How about this (untested) patch?
It's a cleanup as well as a fix, but maybe we should separate the cleanup from the fix...
If you are going to post this, feel free to add
Tested-by: Icenowy Zheng icenowy@aosc.io
Okay, thanks.
(And if you remove the IS_ERR(realfile) part, the tested-by tag still applies.)
Dropping the IS_ERR(realfile) here would mean having to add the same check before relevant fput() calls, which would make it more complex not less.
Or did you mean something else?
Thanks, Miklos