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 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
