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Improve zpl_permission performance 

This function can be frequently called with MAY_EXEC|MAY_NOT_BLOCK
during RCU path walk. Where possible we should try not to break
out of it. In this case we check whether flag ZFS_NO_EXECS_DENIED is
set and check mode (similar to fastexecute check in zfs_acl.c).

Signed-off-by: Andrew Walker <awalker@ixsystems.com>
This commit is contained in:
Andrew Walker 2023-05-04 12:58:47 -04:00 committed by Ameer Hamza
parent d01282fa5a
commit 8a4f609651
1 changed files with 52 additions and 25 deletions
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77
module/os/linux/zfs/zpl_xattr.c
View File

@ -1488,6 +1488,14 @@ static xattr_handler_t zpl_xattr_acl_default_handler = {
#endif /* CONFIG_FS_POSIX_ACL */
/*
* zpl_permission() gets called by linux kernel whenever it checks
* inode_permission via inode->i_op->permission. The general preference
* is to defer to the standard in-kernel permission check (generic_permission)
* wherever possible.
*
* https://www.kernel.org/doc/Documentation/filesystems/vfs.txt
*/
int
#if defined(HAVE_IOPS_PERMISSION_USERNS)
zpl_permission(struct user_namespace *userns, struct inode *ip, int mask)
@ -1532,23 +1540,40 @@ zpl_permission(struct inode *ip, int mask)
}
/*
* Avoid potentially blocking in RCU walk.
* Fast path for execute checks. Do not use zfs_fastaccesschk_execute
* since it may end up granting execute access in presence of explicit
* deny entry for user / group, and it also read the ZFS ACL
* (non-cached) which we wish to avoid in RCU.
*/
if (mask & MAY_NOT_BLOCK) {
return (-ECHILD);
}
cr = CRED();
crhold(cr);
ret = -zfs_access(ITOZ(ip), to_check, V_ACE_MASK, cr);
if (ret != -EPERM && ret != -EACCES) {
crfree(cr);
return (ret);
}
if ((to_check == ACE_EXECUTE) &&
(ITOZ(ip)->z_pflags & ZFS_NO_EXECS_DENIED))
return (0);
/*
* There are some situations in which capabilities
* may allow overriding the DACL.
* inode permission operation may be called in rcu-walk mode
* (mask & MAY_NOT_BLOCK). If in rcu-walk mode, the filesystem must
* check the permission without blocking or storing to the inode.
*
* If a situation is encountered that rcu-walk cannot handle,
* return -ECHILD and it will be called again in ref-walk mode.
*/
cr = CRED();
crhold(cr);
/*
* There are some situations in which capabilities may allow overriding
* the DACL. Skip reading ACL if requested permissions are fully
* satisfied by capabilities.
*/
/*
* CAP_DAC_OVERRIDE may override RWX on directories, and RW on other
* files. Execute may also be overriden if at least one execute bit is
* set. This behavior is not formally documented, but is covered in
* commit messages and code comments in namei.c.
*
* CAP_DAC_READ_SEARCH may bypass file read permission checks and
* directory read and execute permission checks.
*/
if (S_ISDIR(ip->i_mode)) {
#ifdef SB_NFSV4ACL
@ -1565,25 +1590,27 @@ zpl_permission(struct inode *ip, int mask)
crfree(cr);
return (0);
}
crfree(cr);
return (ret);
}
if (to_check == ACE_READ_DATA) {
if (capable(CAP_DAC_READ_SEARCH)) {
crfree(cr);
return (0);
}
}
if (!(mask & MAY_EXEC) ||
(zfs_fastaccesschk_execute(ITOZ(ip), cr) == 0)) {
if (!(mask & MAY_EXEC) || (ip->i_mode & S_IXUGO)) {
if (capable(CAP_DAC_OVERRIDE)) {
crfree(cr);
return (0);
}
}
if ((to_check == ACE_READ_DATA) &&
capable(CAP_DAC_READ_SEARCH)) {
crfree(cr);
return (0);
}
if (mask & MAY_NOT_BLOCK) {
crfree(cr);
return (-ECHILD);
}
ret = -zfs_access(ITOZ(ip), to_check, V_ACE_MASK, cr);
crfree(cr);
return (ret);
}