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7f564528a4
All available gso_type flags are currently in use, so
extend gso_type from 'unsigned short' to 'unsigned int'
to be able to add further flags.
We reorder the struct skb_shared_info to use
two bytes of the four byte hole before dataref.
All fields before dataref are cleared, i.e.
four bytes more than before the change.
The remaining two byte hole is moved to the
beginning of the structure, this protects us
from immediate overwites on out of bound writes
to the sk_buff head.
Structure layout on x86-64 before the change:
struct skb_shared_info {
unsigned char nr_frags; /* 0 1 */
__u8 tx_flags; /* 1 1 */
short unsigned int gso_size; /* 2 2 */
short unsigned int gso_segs; /* 4 2 */
short unsigned int gso_type; /* 6 2 */
struct sk_buff * frag_list; /* 8 8 */
struct skb_shared_hwtstamps hwtstamps; /* 16 8 */
u32 tskey; /* 24 4 */
__be32 ip6_frag_id; /* 28 4 */
atomic_t dataref; /* 32 4 */
/* XXX 4 bytes hole, try to pack */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 12 */
/* sum members: 316, holes: 1, sum holes: 4 */
};
Structure layout on x86-64 after the change:
struct skb_shared_info {
short unsigned int _unused; /* 0 2 */
unsigned char nr_frags; /* 2 1 */
__u8 tx_flags; /* 3 1 */
short unsigned int gso_size; /* 4 2 */
short unsigned int gso_segs; /* 6 2 */
struct sk_buff * frag_list; /* 8 8 */
struct skb_shared_hwtstamps hwtstamps; /* 16 8 */
unsigned int gso_type; /* 24 4 */
u32 tskey; /* 28 4 */
__be32 ip6_frag_id; /* 32 4 */
atomic_t dataref; /* 36 4 */
void * destructor_arg; /* 40 8 */
skb_frag_t frags[17]; /* 48 272 */
/* --- cacheline 5 boundary (320 bytes) --- */
/* size: 320, cachelines: 5, members: 13 */
};
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.