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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 41525f56e2 ("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 <sargun@sargun.me>
Fixes: 41525f56e2 ("fs: refactor ksys_umount")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
master
Al Viro 2021-01-04 15:25:34 -05:00
parent 5c8fe583cc
commit a0a6df9afc
1 changed files with 5 additions and 2 deletions
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7
fs/namespace.c
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@ -1713,8 +1713,6 @@ 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)
@ -1728,6 +1726,7 @@ 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);
@ -1749,6 +1748,10 @@ static 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_at(AT_FDCWD, name, lookup_flags, &path);