Patch "bpf: Permits pointers on stack for helper calls" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Permits pointers on stack for helper calls

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-permits-pointers-on-stack-for-helper-calls.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a5b41af6f59de4d6bf5fc91a52e50e82f7fdc5b3
Author: Yonghong Song <yhs@xxxxxx>
Date:   Wed Dec 9 17:33:49 2020 -0800

    bpf: Permits pointers on stack for helper calls
    
    [ Upstream commit cd17d38f8b28f808c368121041c0a4fa91757e0d ]
    
    Currently, when checking stack memory accessed by helper calls,
    for spills, only PTR_TO_BTF_ID and SCALAR_VALUE are
    allowed.
    
    Song discovered an issue where the below bpf program
      int dump_task(struct bpf_iter__task *ctx)
      {
        struct seq_file *seq = ctx->meta->seq;
        static char[] info = "abc";
        BPF_SEQ_PRINTF(seq, "%s\n", info);
        return 0;
      }
    may cause a verifier failure.
    
    The verifier output looks like:
      ; struct seq_file *seq = ctx->meta->seq;
      1: (79) r1 = *(u64 *)(r1 +0)
      ; BPF_SEQ_PRINTF(seq, "%s\n", info);
      2: (18) r2 = 0xffff9054400f6000
      4: (7b) *(u64 *)(r10 -8) = r2
      5: (bf) r4 = r10
      ;
      6: (07) r4 += -8
      ; BPF_SEQ_PRINTF(seq, "%s\n", info);
      7: (18) r2 = 0xffff9054400fe000
      9: (b4) w3 = 4
      10: (b4) w5 = 8
      11: (85) call bpf_seq_printf#126
       R1_w=ptr_seq_file(id=0,off=0,imm=0) R2_w=map_value(id=0,off=0,ks=4,vs=4,imm=0)
      R3_w=inv4 R4_w=fp-8 R5_w=inv8 R10=fp0 fp-8_w=map_value
      last_idx 11 first_idx 0
      regs=8 stack=0 before 10: (b4) w5 = 8
      regs=8 stack=0 before 9: (b4) w3 = 4
      invalid indirect read from stack off -8+0 size 8
    
    Basically, the verifier complains the map_value pointer at "fp-8" location.
    To fix the issue, if env->allow_ptr_leaks is true, let us also permit
    pointers on the stack to be accessible by the helper.
    
    Reported-by: Song Liu <songliubraving@xxxxxx>
    Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Yonghong Song <yhs@xxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Acked-by: Song Liu <songliubraving@xxxxxx>
    Link: https://lore.kernel.org/bpf/20201210013349.943719-1-yhs@xxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3370f0d476e9..2e09e691a6be 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3759,7 +3759,8 @@ static int check_stack_boundary(struct bpf_verifier_env *env, int regno,
 			goto mark;
 
 		if (state->stack[spi].slot_type[0] == STACK_SPILL &&
-		    state->stack[spi].spilled_ptr.type == SCALAR_VALUE) {
+		    (state->stack[spi].spilled_ptr.type == SCALAR_VALUE ||
+		     env->allow_ptr_leaks)) {
 			__mark_reg_unknown(env, &state->stack[spi].spilled_ptr);
 			for (j = 0; j < BPF_REG_SIZE; j++)
 				state->stack[spi].slot_type[j] = STACK_MISC;