F_MEM_LOCK is accounted by i_size, but fallocate(,FALLOC_FL_KEEP_SIZE,,)
could have added many pages beyond i_size, which would also be held as
Unevictable from memory. The mlock_ucounts check in shmem_fallocate() is
fine, but shmem_memlock_fcntl() needs to check fallocend too. We could
change F_MEM_LOCK accounting to use the max of i_size and fallocend, but
fallocend is obscure: I think it's better just to refuse the F_MEM_LOCK
(with EPERM) if fallocend exceeds (page-rounded) i_size.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/shmem.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 6e53dabe658b..35c0f5c7120e 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2304,7 +2304,10 @@ static int shmem_memlock_fcntl(struct file *file, unsigned int cmd)
inode_lock(inode);
if (cmd == F_MEM_LOCK) {
- if (!info->mlock_ucounts) {
+ if (info->fallocend > DIV_ROUND_UP(inode->i_size, PAGE_SIZE)) {
+ /* locking is accounted by i_size: disallow excess */
+ retval = -EPERM;
+ } else if (!info->mlock_ucounts) {
struct ucounts *ucounts = current_ucounts();
/* capability/rlimit check is down in user_shm_lock */
retval = shmem_lock(file, 1, ucounts);
@@ -2854,9 +2857,10 @@ static long shmem_fallocate(struct file *file, int mode, loff_t offset,
spin_unlock(&inode->i_lock);
/*
- * info->fallocend is only relevant when huge pages might be
+ * info->fallocend is mostly relevant when huge pages might be
* involved: to prevent split_huge_page() freeing fallocated
* pages when FALLOC_FL_KEEP_SIZE committed beyond i_size.
+ * But it is also checked in F_MEM_LOCK validation.
*/
undo_fallocend = info->fallocend;
if (info->fallocend < end)
--
2.26.2
