From 85c59580b30c82aa771aa33b37217a6b6851bc14 Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Thu, 20 Sep 2007 12:45:02 +0400 Subject: [PATCH] locks: Fix potential OOPS in generic_setlease() This code is run under lock_kernel(), which is dropped during sleeping operations, so the following race is possible: CPU1: CPU2: vfs_setlease(); vfs_setlease(); lock_kernel(); lock_kernel(); /* spin */ generic_setlease(): ... for (before = ...) /* here we found some lease after * which we will insert the new one */ fl = locks_alloc_lock(); /* go to sleep in this allocation and * drop the BKL */ generic_setlease(): ... for (before = ...) /* here we find the "before" pointing * at the one we found on CPU1 */ ->fl_change(my_before, arg); lease_modify(); locks_free_lock(); /* and we freed it */ ... unlock_kernel(); locks_insert_lock(before, fl); /* OOPS! We have just tried to add the lease * at the tail of already removed one */ The similar races are already handled in other code - all the allocations are performed before any checks/updates. Thanks to Kamalesh Babulal for testing and for a bug report on an earlier version. Signed-off-by: Pavel Emelyanov Signed-off-by: J. Bruce Fields Cc: Kamalesh Babulal --- fs/locks.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-) diff --git a/fs/locks.c b/fs/locks.c index 282b6c11670a..43dbc7f566fa 100644 --- a/fs/locks.c +++ b/fs/locks.c @@ -1343,6 +1343,7 @@ int fcntl_getlease(struct file *filp) int generic_setlease(struct file *filp, long arg, struct file_lock **flp) { struct file_lock *fl, **before, **my_before = NULL, *lease; + struct file_lock *new_fl = NULL; struct dentry *dentry = filp->f_path.dentry; struct inode *inode = dentry->d_inode; int error, rdlease_count = 0, wrlease_count = 0; @@ -1369,6 +1370,11 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) || (atomic_read(&inode->i_count) > 1))) goto out; + error = -ENOMEM; + new_fl = locks_alloc_lock(); + if (new_fl == NULL) + goto out; + /* * At this point, we know that if there is an exclusive * lease on this file, then we hold it on this filp @@ -1411,18 +1417,15 @@ int generic_setlease(struct file *filp, long arg, struct file_lock **flp) if (!leases_enable) goto out; - error = -ENOMEM; - fl = locks_alloc_lock(); - if (fl == NULL) - goto out; - - locks_copy_lock(fl, lease); + locks_copy_lock(new_fl, lease); + locks_insert_lock(before, new_fl); - locks_insert_lock(before, fl); + *flp = new_fl; + return 0; - *flp = fl; - error = 0; out: + if (new_fl != NULL) + locks_free_lock(new_fl); return error; } EXPORT_SYMBOL(generic_setlease); -- 2.20.1