From 51cc3a6620a6ca934d468bda345678768493f5d8 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 2 Sep 2021 14:53:57 -0700 Subject: fs, mm: fix race in unlinking swapfile We had a recurring situation in which admin procedures setting up swapfiles would race with test preparation clearing away swapfiles; and just occasionally that got stuck on a swapfile "(deleted)" which could never be swapped off. That is not supposed to be possible. 2.6.28 commit f9454548e17c ("don't unlink an active swapfile") admitted that it was leaving a race window open: now close it. may_delete() makes the IS_SWAPFILE check (amongst many others) before inode_lock has been taken on target: now repeat just that simple check in vfs_unlink() and vfs_rename(), after taking inode_lock. Which goes most of the way to fixing the race, but swapon() must also check after it acquires inode_lock, that the file just opened has not already been unlinked. Link: https://lkml.kernel.org/r/e17b91ad-a578-9a15-5e3-4989e0f999b5@google.com Fixes: f9454548e17c ("don't unlink an active swapfile") Signed-off-by: Hugh Dickins Reviewed-by: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/namei.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'fs/namei.c') diff --git a/fs/namei.c b/fs/namei.c index bf6d8a738c59..ff866c07f4d2 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -4024,7 +4024,9 @@ int vfs_unlink(struct user_namespace *mnt_userns, struct inode *dir, return -EPERM; inode_lock(target); - if (is_local_mountpoint(dentry)) + if (IS_SWAPFILE(target)) + error = -EPERM; + else if (is_local_mountpoint(dentry)) error = -EBUSY; else { error = security_inode_unlink(dir, dentry); @@ -4526,6 +4528,10 @@ int vfs_rename(struct renamedata *rd) else if (target) inode_lock(target); + error = -EPERM; + if (IS_SWAPFILE(source) || (target && IS_SWAPFILE(target))) + goto out; + error = -EBUSY; if (is_local_mountpoint(old_dentry) || is_local_mountpoint(new_dentry)) goto out; -- cgit v1.2.3-59-g8ed1b