From: Miklos Szeredi mszeredi@redhat.com
mainline inclusion from mainline-v5.15-rc1 commit 332f606b32b6291a944c8cf23b91f53a6e676525 category: perf bugzilla: https://gitee.com/openeuler/kernel/issues/I6ZCW0 CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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Overlayfs does not cache ACL's (to avoid double caching). Instead it just calls the underlying filesystem's i_op->get_acl(), which will return the cached value, if possible.
In rcu path walk, however, get_cached_acl_rcu() is employed to get the value from the cache, which will fail on overlayfs resulting in dropping out of rcu walk mode. This can result in a big performance hit in certain situations.
Fix by calling ->get_acl() with rcu=true in case of ACL_DONT_CACHE (which indicates pass-through)
Reported-by: garyhuang zjh.20052005@163.com Signed-off-by: Miklos Szeredi mszeredi@redhat.com Conflicts: fs/posix_acl.c Signed-off-by: Zhihao Cheng chengzhihao1@huawei.com Reviewed-by: Zhang Yi yi.zhang@huawei.com Signed-off-by: Yongqiang Liu liuyongqiang13@huawei.com --- fs/overlayfs/inode.c | 7 ++++--- fs/posix_acl.c | 13 ++++++++++++- include/linux/fs.h | 5 +++++ include/linux/posix_acl.h | 3 ++- 4 files changed, 23 insertions(+), 5 deletions(-)
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 3aa33c18cb80..5c82c95e57d2 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -13,6 +13,7 @@ #include <linux/xattr.h> #include <linux/posix_acl.h> #include <linux/ratelimit.h> +#include <linux/namei.h> #include "overlayfs.h"
@@ -427,12 +428,12 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type, bool rcu) const struct cred *old_cred; struct posix_acl *acl;
- if (rcu) - return ERR_PTR(-ECHILD); - if (!IS_ENABLED(CONFIG_FS_POSIX_ACL) || !IS_POSIXACL(realinode)) return NULL;
+ if (rcu) + return get_cached_acl_rcu(realinode, type); + old_cred = ovl_override_creds(inode->i_sb); acl = get_acl(realinode, type); revert_creds(old_cred); diff --git a/fs/posix_acl.c b/fs/posix_acl.c index 8e3fe9cbb28c..f64ed0c7394b 100644 --- a/fs/posix_acl.c +++ b/fs/posix_acl.c @@ -21,6 +21,7 @@ #include <linux/xattr.h> #include <linux/export.h> #include <linux/user_namespace.h> +#include <linux/namei.h>
static struct posix_acl **acl_by_type(struct inode *inode, int type) { @@ -55,7 +56,17 @@ EXPORT_SYMBOL(get_cached_acl);
struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type) { - return rcu_dereference(*acl_by_type(inode, type)); + struct posix_acl *acl = rcu_dereference(*acl_by_type(inode, type)); + + if (acl == ACL_DONT_CACHE && inode->i_op->get_acl2) { + struct posix_acl *ret; + + ret = inode->i_op->get_acl2(inode, type, LOOKUP_RCU); + if (!IS_ERR(ret)) + acl = ret; + } + + return acl; } EXPORT_SYMBOL(get_cached_acl_rcu);
diff --git a/include/linux/fs.h b/include/linux/fs.h index bd3e09a3c9a9..9729cfad4175 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -594,6 +594,11 @@ static inline void mapping_allow_writable(struct address_space *mapping)
struct posix_acl; #define ACL_NOT_CACHED ((void *)(-1)) +/* + * ACL_DONT_CACHE is for stacked filesystems, that rely on underlying fs to + * cache the ACL. This also means that ->get_acl2() can be called in RCU mode + * with the LOOKUP_RCU flag. + */ #define ACL_DONT_CACHE ((void *)(-3))
static inline struct posix_acl * diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h index 540595a321a7..0c842d07091a 100644 --- a/include/linux/posix_acl.h +++ b/include/linux/posix_acl.h @@ -71,6 +71,8 @@ extern int __posix_acl_chmod(struct posix_acl **, gfp_t, umode_t); extern struct posix_acl *get_posix_acl(struct inode *, int); extern int set_posix_acl(struct inode *, int, struct posix_acl *);
+struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type); + #ifdef CONFIG_FS_POSIX_ACL extern int posix_acl_chmod(struct inode *, umode_t); extern int posix_acl_create(struct inode *, umode_t *, struct posix_acl **, @@ -81,7 +83,6 @@ extern int simple_set_acl(struct inode *, struct posix_acl *, int); extern int simple_acl_create(struct inode *, struct inode *);
struct posix_acl *get_cached_acl(struct inode *inode, int type); -struct posix_acl *get_cached_acl_rcu(struct inode *inode, int type); void set_cached_acl(struct inode *inode, int type, struct posix_acl *acl); void forget_cached_acl(struct inode *inode, int type); void forget_all_cached_acls(struct inode *inode);