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xsk: Try to make xdp_umem_reg extension a bit more future-proof

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We recently found out that extending xsk_umem_reg might be a bit
complicated due to not enforcing padding to be zero [0]. Add
a couple of things to make it less error-prone:
1. Remove xdp_umem_reg_v2 since its sizeof is the same as xdp_umem_reg
2. Add BUILD_BUG_ON that checks that the size of xdp_umem_reg_v1 is less
   than xdp_umem_reg; presumably, when we get to v2, there is gonna
   be a similar line to enforce that sizeof(v2) > sizeof(v1)
3. Add BUILD_BUG_ON to make sure the last field plus its size matches
   the overall struct size. The intent is to demonstrate that we don't
   have any lingering padding.

0: https://lore.kernel.org/bpf/ZqI29QE+5JnkdPmE@boxer/T/#me03113f7c2458fd08f3c4114a7a9472ac3646c98

Reported-by: Julian Schindel <mail@arctic-alpaca.de>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://lore.kernel.org/r/20240726222048.1397869-1-sdf@fomichev.me
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Stanislav Fomichev 2024-07-26 15:20:48 -07:00 committed by Martin KaFai Lau
parent 1cbe8143fd
commit 32654bbd63
1 changed files with 12 additions and 11 deletions
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23
net/xdp/xsk.c
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@ -1320,14 +1320,6 @@ struct xdp_umem_reg_v1 {
__u32 headroom;
};
struct xdp_umem_reg_v2 {
__u64 addr; /* Start of packet data area */
__u64 len; /* Length of packet data area */
__u32 chunk_size;
__u32 headroom;
__u32 flags;
};
static int xsk_setsockopt(struct socket *sock, int level, int optname,
sockptr_t optval, unsigned int optlen)
{
@ -1371,10 +1363,19 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
if (optlen < sizeof(struct xdp_umem_reg_v1))
return -EINVAL;
else if (optlen < sizeof(struct xdp_umem_reg_v2))
mr_size = sizeof(struct xdp_umem_reg_v1);
else if (optlen < sizeof(mr))
mr_size = sizeof(struct xdp_umem_reg_v2);
mr_size = sizeof(struct xdp_umem_reg_v1);
BUILD_BUG_ON(sizeof(struct xdp_umem_reg_v1) >= sizeof(struct xdp_umem_reg));
/* Make sure the last field of the struct doesn't have
* uninitialized padding. All padding has to be explicit
* and has to be set to zero by the userspace to make
* struct xdp_umem_reg extensible in the future.
*/
BUILD_BUG_ON(offsetof(struct xdp_umem_reg, tx_metadata_len) +
sizeof_field(struct xdp_umem_reg, tx_metadata_len) !=
sizeof(struct xdp_umem_reg));
if (copy_from_sockptr(&mr, optval, mr_size))
return -EFAULT;