[PATCH 5.10 138/152] umount(2): move the flag validity checks first
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2021-01-18 11:59:44
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From: Al Viro <viro@zeniv.linux.org.uk>
commit a0a6df9afcaf439a6b4c88a3b522e3d05fdef46f upstream.
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 <redacted>
Fixes: 41525f56e256 ("fs: refactor ksys_umount")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/namespace.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c@@ -1713,8 +1713,6 @@ static int can_umount(const struct path { 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)
@@ -1728,6 +1726,7 @@ static int can_umount(const struct path return 0; } +// caller is responsible for flags being sane int path_umount(struct path *path, int flags) { struct mount *mnt = real_mount(path->mnt);
@@ -1749,6 +1748,10 @@ static int ksys_umount(char __user *name 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_at(AT_FDCWD, name, lookup_flags, &path);