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bpf: reference may_access_skb() from __bpf_prog_run() 

It took me quite some time to figure out how this was linked,
so in order to save the next person the effort of finding it
add a comment in __bpf_prog_run() that indicates what exactly
determines that a program can access the ctx == skb.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Johannes Berg 2017-04-11 12:10:58 +02:00 committed by David S. Miller
parent 17c3060b17
commit 96a94cc515
1 changed files with 6 additions and 6 deletions
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12
kernel/bpf/core.c
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@ -1162,12 +1162,12 @@ out:
LD_ABS_W: /* BPF_R0 = ntohl(*(u32 *) (skb->data + imm32)) */
off = IMM;
load_word:
/* BPF_LD + BPD_ABS and BPF_LD + BPF_IND insns are
* only appearing in the programs where ctx ==
* skb. All programs keep 'ctx' in regs[BPF_REG_CTX]
* == BPF_R6, bpf_convert_filter() saves it in BPF_R6,
* internal BPF verifier will check that BPF_R6 ==
* ctx.
/* BPF_LD + BPD_ABS and BPF_LD + BPF_IND insns are only
* appearing in the programs where ctx == skb
* (see may_access_skb() in the verifier). All programs
* keep 'ctx' in regs[BPF_REG_CTX] == BPF_R6,
* bpf_convert_filter() saves it in BPF_R6, internal BPF
* verifier will check that BPF_R6 == ctx.
*
* BPF_ABS and BPF_IND are wrappers of function calls,
* so they scratch BPF_R1-BPF_R5 registers, preserve