| Message ID | 20200728163836.562074-3-hch@lst.de |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | sockptr_t fixes v2 | expand |
From: Christoph Hellwig <hch@lst.de> > Sent: 28 July 2020 17:39 > > While the kernel in general is not strict aliasing safe we can trivially > do that in sockptr_is_null without affecting code generation, so always > check the actually assigned union member. Even with 'strict aliasing' gcc (at least) guarantees that the members of a union alias each other. It is about the only way so safely interpret a float as an int. So when sockptr_t is a union testing either member is enough. When it is a structure the changed form almost certainly adds code. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On Wednesday 2020-07-29 10:04, David Laight wrote: >From: Christoph Hellwig <hch@lst.de> >> Sent: 28 July 2020 17:39 >> >> While the kernel in general is not strict aliasing safe we can trivially >> do that in sockptr_is_null without affecting code generation, so always >> check the actually assigned union member. > >Even with 'strict aliasing' gcc (at least) guarantees that >the members of a union alias each other. >It is about the only way so safely interpret a float as an int. The only? float given; int i; memcpy(&i, &given, sizeof(i)); BUILD_BUG_ON(sizeof(i) > sizeof(given));
diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h index 7d5cdb2b30b5f0..b13ea1422f93a5 100644 --- a/include/linux/sockptr.h +++ b/include/linux/sockptr.h @@ -64,7 +64,9 @@ static inline int __must_check init_user_sockptr(sockptr_t *sp, void __user *p) static inline bool sockptr_is_null(sockptr_t sockptr) { - return !sockptr.user && !sockptr.kernel; + if (sockptr_is_kernel(sockptr)) + return !sockptr.kernel; + return !sockptr.user; } static inline int copy_from_sockptr(void *dst, sockptr_t src, size_t size)
While the kernel in general is not strict aliasing safe we can trivially do that in sockptr_is_null without affecting code generation, so always check the actually assigned union member. Reported-by: Jan Engelhardt <jengelh@inai.de> Signed-off-by: Christoph Hellwig <hch@lst.de> --- include/linux/sockptr.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)