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authorHugh Dickins <hughd@google.com>2021-09-02 14:53:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-03 09:58:11 -0700
commit51cc3a6620a6ca934d468bda345678768493f5d8 (patch)
tree027998d57756dcca6c4c8717a0b8b29e499ca5c0 /mm/swapfile.c
parent9857a17f206ff374aea78bccfb687f145368be2e (diff)
downloadlinux-51cc3a6620a6ca934d468bda345678768493f5d8.tar.bz2
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 <hughd@google.com> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1e07d1c776f2..7527afd95284 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3130,6 +3130,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
struct filename *name;
struct file *swap_file = NULL;
struct address_space *mapping;
+ struct dentry *dentry;
int prio;
int error;
union swap_header *swap_header;
@@ -3173,6 +3174,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
p->swap_file = swap_file;
mapping = swap_file->f_mapping;
+ dentry = swap_file->f_path.dentry;
inode = mapping->host;
error = claim_swapfile(p, inode);
@@ -3180,6 +3182,10 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
goto bad_swap;
inode_lock(inode);
+ if (d_unlinked(dentry) || cant_mount(dentry)) {
+ error = -ENOENT;
+ goto bad_swap_unlock_inode;
+ }
if (IS_SWAPFILE(inode)) {
error = -EBUSY;
goto bad_swap_unlock_inode;