locks: require that flock->l_pid be set to 0 for file-private locks

Neil Brown suggested potentially overloading the l_pid value as a "lock
context" field for file-private locks. While I don't think we will
probably want to do that here, it's probably a good idea to ensure that
in the future we could extend this API without breaking existing
callers.

Typically the l_pid value is ignored for incoming struct flock
arguments, serving mainly as a place to return the pid of the owner if
there is a conflicting lock. For file-private locks, require that it
currently be set to 0 and return EINVAL if it isn't. If we eventually
want to make a non-zero l_pid mean something, then this will help ensure
that we don't break legacy programs that are using file-private locks.

Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/fs/locks.c b/fs/locks.c
index 3b54b98236eeeccf2588eadb5a6df82b45d591f4..09d6c8c33c815d168b5bbaf5a36619a21ccf322e 100644 (file)
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1931,6 +1931,10 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock __user *l)
                goto out;
 
        if (cmd == F_GETLKP) {
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_GETLK;
                file_lock.fl_flags |= FL_FILE_PVT;
                file_lock.fl_owner = (fl_owner_t)filp;
@@ -2062,11 +2066,19 @@ again:
         */
        switch (cmd) {
        case F_SETLKP:
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_SETLK;
                file_lock->fl_flags |= FL_FILE_PVT;
                file_lock->fl_owner = (fl_owner_t)filp;
                break;
        case F_SETLKPW:
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_SETLKW;
                file_lock->fl_flags |= FL_FILE_PVT;
                file_lock->fl_owner = (fl_owner_t)filp;
@@ -2121,6 +2133,10 @@ int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 __user *l)
                goto out;
 
        if (cmd == F_GETLKP) {
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_GETLK64;
                file_lock.fl_flags |= FL_FILE_PVT;
                file_lock.fl_owner = (fl_owner_t)filp;
@@ -2185,11 +2201,19 @@ again:
         */
        switch (cmd) {
        case F_SETLKP:
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_SETLK64;
                file_lock->fl_flags |= FL_FILE_PVT;
                file_lock->fl_owner = (fl_owner_t)filp;
                break;
        case F_SETLKPW:
+               error = -EINVAL;
+               if (flock.l_pid != 0)
+                       goto out;
+
                cmd = F_SETLKW64;
                file_lock->fl_flags |= FL_FILE_PVT;
                file_lock->fl_owner = (fl_owner_t)filp;