From 359222f02ff7b69668a493207e3b84d53195f818 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 25 May 2021 16:07:48 +0200 Subject: [PATCH] quota: Change quotactl_path() systcall to an fd-based one Some users have pointed out that path-based syscalls are problematic in some environments and at least directory fd argument and possibly also resolve flags are desirable for such syscalls. Rather than reimplementing all details of pathname lookup and following where it may eventually evolve, let's go for full file descriptor based syscall similar to how ioctl(2) works since the beginning. Managing of quotas isn't performance sensitive so the extra overhead of open does not matter and we are able to consume O_PATH descriptors as well which makes open cheap anyway. Also for frequent operations (such as retrieving usage information for all users) we can reuse single fd and in fact get even better performance as well as avoiding races with possible remounts etc. Signed-off-by: Jan Kara --- fs/quota/quota.c | 27 ++++++++++++--------------- include/linux/syscalls.h | 4 ++-- 2 files changed, 14 insertions(+), 17 deletions(-) diff --git a/fs/quota/quota.c b/fs/quota/quota.c index 05e4bd9ab6d6..8450bb6186f4 100644 --- a/fs/quota/quota.c +++ b/fs/quota/quota.c @@ -968,31 +968,29 @@ SYSCALL_DEFINE4(quotactl, unsigned int, cmd, const char __user *, special, return ret; } -SYSCALL_DEFINE4(quotactl_path, unsigned int, cmd, const char __user *, - mountpoint, qid_t, id, void __user *, addr) +SYSCALL_DEFINE4(quotactl_fd, unsigned int, fd, unsigned int, cmd, + qid_t, id, void __user *, addr) { struct super_block *sb; - struct path mountpath; unsigned int cmds = cmd >> SUBCMDSHIFT; unsigned int type = cmd & SUBCMDMASK; + struct fd f = fdget_raw(fd); int ret; - if (type >= MAXQUOTAS) - return -EINVAL; + if (!f.file) + return -EBADF; - ret = user_path_at(AT_FDCWD, mountpoint, - LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT, &mountpath); - if (ret) - return ret; - - sb = mountpath.mnt->mnt_sb; + ret = -EINVAL; + if (type >= MAXQUOTAS) + goto out; if (quotactl_cmd_write(cmds)) { - ret = mnt_want_write(mountpath.mnt); + ret = mnt_want_write(f.file->f_path.mnt); if (ret) goto out; } + sb = f.file->f_path.mnt->mnt_sb; if (quotactl_cmd_onoff(cmds)) down_write(&sb->s_umount); else @@ -1006,9 +1004,8 @@ SYSCALL_DEFINE4(quotactl_path, unsigned int, cmd, const char __user *, up_read(&sb->s_umount); if (quotactl_cmd_write(cmds)) - mnt_drop_write(mountpath.mnt); + mnt_drop_write(f.file->f_path.mnt); out: - path_put(&mountpath); - + fdput(f); return ret; } diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index 050511e8f1f8..586128d5c3b8 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -485,8 +485,8 @@ asmlinkage long sys_pipe2(int __user *fildes, int flags); /* fs/quota.c */ asmlinkage long sys_quotactl(unsigned int cmd, const char __user *special, qid_t id, void __user *addr); -asmlinkage long sys_quotactl_path(unsigned int cmd, const char __user *mountpoint, - qid_t id, void __user *addr); +asmlinkage long sys_quotactl_fd(unsigned int fd, unsigned int cmd, qid_t id, + void __user *addr); /* fs/readdir.c */ asmlinkage long sys_getdents64(unsigned int fd, -- 2.26.2