From 3d435413340ed5cf7bc0a974a325a8095b08b6f6 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Mon, 4 Jan 2021 15:25:34 -0500 Subject: [PATCH] BACKPORT: umount(2): move the flag validity checks first Unfortunately, there's userland code that used to rely upon these checks being done before anything else to check for UMOUNT_NOFOLLOW support. That broke in 41525f56e256 ("fs: refactor ksys_umount"). Separate those from the rest of checks and move them to ksys_umount(); unlike everything else in there, this can be sanely done there. Reported-by: Sargun Dhillon Fixes: 41525f56e256 ("fs: refactor ksys_umount") Signed-off-by: Al Viro Signed-off-by: mrsrimar22 Signed-off-by: chrisl7 --- fs/namespace.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/namespace.c b/fs/namespace.c index ae1463651549..c114df2f83fa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1700,8 +1700,6 @@ static int can_umount(const struct path *path, int flags) { struct mount *mnt = real_mount(path->mnt); - if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW)) - return -EINVAL; if (!may_mount()) return -EPERM; if (path->dentry != path->mnt->mnt_root) @@ -1715,6 +1713,7 @@ static int can_umount(const struct path *path, int flags) return 0; } +// caller is responsible for flags being sane int path_umount(struct path *path, int flags) { struct mount *mnt = real_mount(path->mnt); @@ -1736,6 +1735,10 @@ int ksys_umount(char __user *name, int flags) struct path path; int ret; + // basic validity checks done first + if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW)) + return -EINVAL; + if (!(flags & UMOUNT_NOFOLLOW)) lookup_flags |= LOOKUP_FOLLOW; ret = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);