[PATCH AUTOSEL 4.19 310/671] afs: Fix AFS file locking to allow fine grained locks

Sasha Levin
2020-01-16T19:00:17Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit 68ce801ffd82e72d5005ab5458e8b9e59f24d9cc ]

Fix AFS file locking to allow fine grained locks as some applications, such
as firefox, won't work if they can't take such locks on certain state files
- thereby preventing the use of kAFS to distribute a home directory.

Note that this cannot be made completely functional as the protocol only
has provision for whole-file locks, so there exists the possibility of a
process deadlocking itself by getting a partial read-lock on a file first
and then trying to get a non-overlapping write-lock - but we got the
server's read lock with the first lock, so we're now stuck.

OpenAFS solves this by just granting any partial-range lock directly
without consulting the server - and hoping there's no remote collision. I
want to implement that in a separate patch and it requires a bit more
thought.

Fixes: 8d6c554126b8 ("AFS: implement file locking")
Reported-by: Jonathan Billings <jsbillings@jsbillings.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/afs/flock.c | 23 +++++++++--------------
1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/fs/afs/flock.c b/fs/afs/flock.c
index 1bb300ef362b..dffbb456629c 100644
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@@ -432,10 +432,6 @@ static int afs_do_setlk(struct file *file, struct file_lock *fl)

_enter("{%x:%u},%u", vnode->fid.vid, vnode->fid.vnode, fl->fl_type);

- /* only whole-file locks are supported */
- if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
- return -EINVAL;
-
fl->fl_ops = &afs_lock_ops;
INIT_LIST_HEAD(&fl->fl_u.afs.link);
fl->fl_u.afs.state = AFS_LOCK_PENDING;
@@ -587,10 +583,6 @@ static int afs_do_unlk(struct file *file, struct file_lock *fl)
/* Flush all pending writes before doing anything with locks. */
vfs_fsync(file, 0);

- /* only whole-file unlocks are supported */
- if (fl->fl_start != 0 || fl->fl_end != OFFSET_MAX)
- return -EINVAL;
-
ret = posix_lock_file(file, fl, NULL);
_leave(" = %d [%u]", ret, vnode->lock_state);
return ret;
@@ -618,12 +610,15 @@ static int afs_do_getlk(struct file *file, struct file_lock *fl)
goto error;

lock_count = READ_ONCE(vnode->status.lock_count);
- if (lock_count > 0)
- fl->fl_type = F_RDLCK;
- else
- fl->fl_type = F_WRLCK;
- fl->fl_start = 0;
- fl->fl_end = OFFSET_MAX;
+ if (lock_count != 0) {
+ if (lock_count > 0)
+ fl->fl_type = F_RDLCK;
+ else
+ fl->fl_type = F_WRLCK;
+ fl->fl_start = 0;
+ fl->fl_end = OFFSET_MAX;
+ fl->fl_pid = 0;
+ }
}

ret = 0;
--
2.20.1