Messages in this thread | | | Date | Fri, 7 Jun 2019 21:02:25 -0700 | From | Kees Cook <> | Subject | Re: [PATCH v16 08/16] fs, arm64: untag user pointers in copy_mount_options |
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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@arm.com> > Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
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@chromium.org>
-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
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