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

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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: Lorenz Bauer <lmb@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Lorenz Bauer <lmb@isovalent.com>
Link: https://lore.kernel.org/bpf/20230406234205.323208-15-andrii@kernel.org
This commit is contained in:
Andrii Nakryiko 2023-04-06 16:42:00 -07:00 committed by Daniel Borkmann
parent bdcab4144f
commit fac08d45e2
1 changed files with 25 additions and 17 deletions
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42
kernel/bpf/log.c
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@ -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 @@ skip_log_rotate:
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;