CIFS: Do not permit write to a range mandatory locked with a read lock

We don't need to permit a write to the area locked with a read lock
by any process including the process that issues the write.

Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

1 files changed, 18 insertions, 9 deletions

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index bceffa8c034..ebebbb2bc1f 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -759,10 +759,15 @@ cifs_del_lock_waiters(struct cifsLockInfo *lock)
         }
 }
 
+#define CIFS_LOCK_OP    0
+#define CIFS_READ_OP    1
+#define CIFS_WRITE_OP   2
+
+/* @rw_check : 0 - no op, 1 - read, 2 - write */
 static bool
 cifs_find_fid_lock_conflict(struct cifs_fid_locks *fdlocks, __u64 offset,
                             __u64 length, __u8 type, struct cifsFileInfo *cfile,
-                            struct cifsLockInfo **conf_lock, bool rw_check)
+                            struct cifsLockInfo **conf_lock, int rw_check)
 {
         struct cifsLockInfo *li;
         struct cifsFileInfo *cur_cfile = fdlocks->cfile;
@@ -772,9 +777,13 @@ cifs_find_fid_lock_conflict(struct cifs_fid_locks *fdlocks, __u64 offset,
                 if (offset + length <= li->offset ||
                     offset >= li->offset + li->length)
                         continue;
-                if (rw_check && server->ops->compare_fids(cfile, cur_cfile) &&
-                    current->tgid == li->pid)
-                        continue;
+                if (rw_check != CIFS_LOCK_OP && current->tgid == li->pid &&
+                    server->ops->compare_fids(cfile, cur_cfile)) {
+                        /* shared lock prevents write op through the same fid */
+                        if (!(li->type & server->vals->shared_lock_type) ||
+                            rw_check != CIFS_WRITE_OP)
+                                continue;
+                }
                 if ((type & server->vals->shared_lock_type) &&
                     ((server->ops->compare_fids(cfile, cur_cfile) &&
                      current->tgid == li->pid) || type == li->type))
@@ -789,7 +798,7 @@ cifs_find_fid_lock_conflict(struct cifs_fid_locks *fdlocks, __u64 offset,
 bool
 cifs_find_lock_conflict(struct cifsFileInfo *cfile, __u64 offset, __u64 length,
                         __u8 type, struct cifsLockInfo **conf_lock,
-                        bool rw_check)
+                        int rw_check)
 {
         bool rc = false;
         struct cifs_fid_locks *cur;
@@ -825,7 +834,7 @@ cifs_lock_test(struct cifsFileInfo *cfile, __u64 offset, __u64 length,
         down_read(&cinode->lock_sem);
 
         exist = cifs_find_lock_conflict(cfile, offset, length, type,
-                                        &conf_lock, false);
+                                        &conf_lock, CIFS_LOCK_OP);
         if (exist) {
                 flock->fl_start = conf_lock->offset;
                 flock->fl_end = conf_lock->offset + conf_lock->length - 1;
@@ -872,7 +881,7 @@ try_again:
         down_write(&cinode->lock_sem);
 
         exist = cifs_find_lock_conflict(cfile, lock->offset, lock->length,
-                                        lock->type, &conf_lock, false);
+                                        lock->type, &conf_lock, CIFS_LOCK_OP);
         if (!exist && cinode->can_cache_brlcks) {
                 list_add_tail(&lock->llist, &cfile->llist->locks);
                 up_write(&cinode->lock_sem);
@@ -2466,7 +2475,7 @@ cifs_writev(struct kiocb *iocb, const struct iovec *iov,
         down_read(&cinode->lock_sem);
         if (!cifs_find_lock_conflict(cfile, pos, iov_length(iov, nr_segs),
                                      server->vals->exclusive_lock_type, NULL,
-                                     true)) {
+                                     CIFS_WRITE_OP)) {
                 mutex_lock(&inode->i_mutex);
                 rc = __generic_file_aio_write(iocb, iov, nr_segs,
                                                &iocb->ki_pos);
@@ -2901,7 +2910,7 @@ cifs_strict_readv(struct kiocb *iocb, const struct iovec *iov,
         down_read(&cinode->lock_sem);
         if (!cifs_find_lock_conflict(cfile, pos, iov_length(iov, nr_segs),
                                      tcon->ses->server->vals->shared_lock_type,
-                                     NULL, true))
+                                     NULL, CIFS_READ_OP))
                 rc = generic_file_aio_read(iocb, iov, nr_segs, pos);
         up_read(&cinode->lock_sem);
         return rc;