Commit fac08d45 authored by Andrii Nakryiko's avatar Andrii Nakryiko Committed by Daniel Borkmann
Browse files

bpf: Relax log_buf NULL conditions when log_level>0 is requested 



Drop the log_size>0 and log_buf!=NULL condition when log_level>0. This
allows users to request log_true_size of a full log without providing
actual (even if small) log buffer. Verifier log handling code was mostly
ready to handle NULL log->ubuf, so only few small changes were necessary
to prevent NULL log->ubuf from causing problems.

Note, that if user provided NULL log_buf with log_level>0 we don't
consider this a log truncation, and thus won't return -ENOSPC.

We also enforce that either (log_buf==NULL && log_size==0) or
(log_buf!=NULL && log_size>0).

Suggested-by: default avatarLorenz Bauer <lmb@isovalent.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarLorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-15-andrii@kernel.org
parent bdcab414

kernel/bpf/log.c

+25 −17
Original line number Diff line number Diff line
@@ -12,8 +12,17 @@ 


static bool bpf_verifier_log_attr_valid(const struct bpf_verifier_log *log)

{

	return log->len_total > 0 && log->len_total <= UINT_MAX >> 2 &&

	       log->level && log->ubuf && !(log->level & ~BPF_LOG_MASK);

	/* ubuf and len_total should both be specified (or not) together */

	if (!!log->ubuf != !!log->len_total)

		return false;

	/* log buf without log_level is meaningless */

	if (log->ubuf && log->level == 0)

		return false;

	if (log->level & ~BPF_LOG_MASK)

		return false;

	if (log->len_total > UINT_MAX >> 2)

		return false;

	return true;

}



int bpf_vlog_init(struct bpf_verifier_log *log, u32 log_level,
@@ -89,9 +98,15 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, 
			new_start = new_end - log->len_total;

		else

			new_start = log->start_pos;



		log->start_pos = new_start;

		log->end_pos = new_end - 1; /* don't count terminating '\0' */



		if (!log->ubuf)

			return;



		new_n = min(n, log->len_total);

		cur_pos = new_end - new_n;



		div_u64_rem(cur_pos, log->len_total, &buf_start);

		div_u64_rem(new_end, log->len_total, &buf_end);

		/* new_end and buf_end are exclusive indices, so if buf_end is
@@ -101,12 +116,6 @@ void bpf_verifier_vlog(struct bpf_verifier_log *log, const char *fmt, 
		if (buf_end == 0)

			buf_end = log->len_total;



		log->start_pos = new_start;

		log->end_pos = new_end - 1; /* don't count terminating '\0' */



		if (!log->ubuf)

			return;



		/* if buf_start > buf_end, we wrapped around;

		 * if buf_start == buf_end, then we fill ubuf completely; we

		 * can't have buf_start == buf_end to mean that there is
@@ -156,12 +165,15 @@ void bpf_vlog_reset(struct bpf_verifier_log *log, u64 new_pos) 
	if (log->end_pos < log->start_pos)

		log->start_pos = log->end_pos;



	if (!log->ubuf)

		return;



	if (log->level & BPF_LOG_FIXED)

		pos = log->end_pos + 1;

	else

		div_u64_rem(new_pos, log->len_total, &pos);



	if (log->ubuf && pos < log->len_total && put_user(zero, log->ubuf + pos))

	if (pos < log->len_total && put_user(zero, log->ubuf + pos))

		log->ubuf = NULL;

}
@@ -211,11 +223,6 @@ static int bpf_vlog_reverse_ubuf(struct bpf_verifier_log *log, int start, int en 
	return 0;

}



static bool bpf_vlog_truncated(const struct bpf_verifier_log *log)

{

	return log->len_max > log->len_total;

}



int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual)

{

	u32 sublen;
@@ -228,7 +235,7 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) 
	if (!log->ubuf)

		goto skip_log_rotate;

	/* If we never truncated log, there is nothing to move around. */

	if ((log->level & BPF_LOG_FIXED) || log->start_pos == 0)

	if (log->start_pos == 0)

		goto skip_log_rotate;



	/* Otherwise we need to rotate log contents to make it start from the
@@ -283,7 +290,8 @@ int bpf_vlog_finalize(struct bpf_verifier_log *log, u32 *log_size_actual) 
	if (!!log->ubuf != !!log->len_total)

		return -EFAULT;



	if (bpf_vlog_truncated(log))

	/* did truncation actually happen? */

	if (log->ubuf && log->len_max > log->len_total)

		return -ENOSPC;



	return 0;