On Mon, Jun 24, 2019 at 04:32:52PM +0200, Andrey Konovalov wrote: > This patch is a part of a series that extends 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: Khalid Aziz <khalid.aziz@xxxxxxxxxx> > Reviewed-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx> > Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> > --- > fs/namespace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/namespace.c b/fs/namespace.c > index 7660c2749c96..ec78f7223917 100644 > --- a/fs/namespace.c > +++ b/fs/namespace.c > @@ -2994,7 +2994,7 @@ 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; I think this patch needs an ack from Al Viro (cc'ed). -- Catalin
