On Sat, Jun 8, 2019 at 6:02 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Mon, Jun 03, 2019 at 06:55:10PM +0200, Andrey Konovalov wrote: > > This patch is a part of a series that extends arm64 kernel ABI to allow to > > pass tagged user pointers (with the top byte set to something else other > > than 0x00) as syscall arguments. > > > > In copy_mount_options a user address is being subtracted from TASK_SIZE. > > If the address is lower than TASK_SIZE, the size is calculated to not > > allow the exact_copy_from_user() call to cross TASK_SIZE boundary. > > However if the address is tagged, then the size will be calculated > > incorrectly. > > > > Untag the address before subtracting. > > > > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > > One thing I just noticed in the commit titles... "arm64" is in the > prefix, but these are arch-indep areas. Should the ", arm64" be left > out? > > I would expect, instead: > > fs/namespace: untag user pointers in copy_mount_options Hm, I've added the arm64 tag in all of the patches because they are related to changes in arm64 kernel ABI. I can remove it from all the patches that only touch common code if you think that it makes sense. Thanks! > > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > -Kees > > > --- > > fs/namespace.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/fs/namespace.c b/fs/namespace.c > > index b26778bdc236..2e85712a19ed 100644 > > --- a/fs/namespace.c > > +++ b/fs/namespace.c > > @@ -2993,7 +2993,7 @@ void *copy_mount_options(const void __user * data) > > * the remainder of the page. > > */ > > /* copy_from_user cannot cross TASK_SIZE ! */ > > - size = TASK_SIZE - (unsigned long)data; > > + size = TASK_SIZE - (unsigned long)untagged_addr(data); > > if (size > PAGE_SIZE) > > size = PAGE_SIZE; > > > > -- > > 2.22.0.rc1.311.g5d7573a151-goog > > > > -- > Kees Cook
