From 2a3a2a3f35249412e35fbb48b743348c40373409 Mon Sep 17 00:00:00 2001
From: Miklos Szeredi <mszeredi@redhat.com>
Date: Thu, 1 Sep 2016 11:11:59 +0200
Subject: [PATCH] ovl: don't cache acl on overlay layer
Some operations (setxattr/chmod) can make the cached acl stale. We either
need to clear overlay's acl cache for the affected inode or prevent acl
caching on the overlay altogether. Preventing caching has the following
advantages:
- no double caching, less memory used
- overlay cache doesn't go stale when fs clears it's own cache
Possible disadvantage is performance loss. If that becomes a problem
get_acl() can be optimized for overlayfs.
This patch disables caching by pre setting i_*acl to a value that
- has bit 0 set, so is_uncached_acl() will return true
- is not equal to ACL_NOT_CACHED, so get_acl() will not overwrite it
The constant -3 was chosen for this purpose.
Fixes: 39a25b2b3762 ("ovl: define ->get_acl() for overlay inodes")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
fs/overlayfs/inode.c | 3 +++
include/linux/fs.h | 1 +
2 files changed, 4 insertions(+)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index d50d1ead1b6f..47a4f33df47b 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -416,6 +416,9 @@ static void ovl_fill_inode(struct inode *inode, umode_t mode)
inode->i_ino = get_next_ino();
inode->i_mode = mode;
inode->i_flags |= S_NOCMTIME;
+#ifdef CONFIG_FS_POSIX_ACL
+ inode->i_acl = inode->i_default_acl = ACL_DONT_CACHE;
+#endif
mode &= S_IFMT;
switch (mode) {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3523bf62f328..901e25d495cc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -574,6 +574,7 @@ static inline void mapping_allow_writable(struct address_space *mapping)
struct posix_acl;
#define ACL_NOT_CACHED ((void *)(-1))
+#define ACL_DONT_CACHE ((void *)(-3))
static inline struct posix_acl *
uncached_acl_sentinel(struct task_struct *task)