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Commit 96a94cc5 authored by Johannes Berg's avatar Johannes Berg Committed by David S. Miller
Browse files

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: default avatarJohannes Berg <johannes.berg@intel.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 17c3060b

kernel/bpf/core.c

+6 −6
Original line number Diff line number Diff line
@@ -1162,12 +1162,12 @@ static unsigned int __bpf_prog_run(void *ctx, const struct bpf_insn *insn) 
	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