Re: [PATCH iproute2 net-next] bpf: Fix number of retries when growing log buffer

[Stephen Hemminger]

On Wed,  7 Dec 2016 10:47:59 +0100
Thomas Graf  wrote:

> The log buffer is automatically grown when the verifier output does not
> fit into the default buffer size. The number of growing attempts was
> not sufficient to reach the maximum buffer size so far.
> 
> Perform 9 iterations to reach max and let the 10th one fail.
> 
> j:0 i:65536 max:16777215
> j:1 i:131072max:16777215
> j:2 i:262144max:16777215
> j:3 i:524288max:16777215
> j:4 i:1048576   max:16777215
> j:5 i:2097152   max:16777215
> j:6 i:4194304   max:16777215
> j:7 i:8388608   max:16777215
> j:8 i:16777216  max:16777215
> 
> Signed-off-by: Thomas Graf 
> Acked-by: Daniel Borkmann 

Applied to net-next

[PATCH iproute2 net-next] bpf: Fix number of retries when growing log buffer

[Thomas Graf]

The log buffer is automatically grown when the verifier output does not
fit into the default buffer size. The number of growing attempts was
not sufficient to reach the maximum buffer size so far.

Perform 9 iterations to reach max and let the 10th one fail.

j:0 i:65536 max:16777215
j:1 i:131072max:16777215
j:2 i:262144max:16777215
j:3 i:524288max:16777215
j:4 i:1048576   max:16777215
j:5 i:2097152   max:16777215
j:6 i:4194304   max:16777215
j:7 i:8388608   max:16777215
j:8 i:16777216  max:16777215

Signed-off-by: Thomas Graf 
Acked-by: Daniel Borkmann 
---
 lib/bpf.c | 11 +++
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/lib/bpf.c b/lib/bpf.c
index 8a5b84b..f3dace2 100644
--- a/lib/bpf.c
+++ b/lib/bpf.c
@@ -912,15 +912,18 @@ bpf_dump_error(struct bpf_elf_ctx *ctx, const char 
*format, ...)
 
 static int bpf_log_realloc(struct bpf_elf_ctx *ctx)
 {
+   const size_t log_max = UINT_MAX >> 8;
size_t log_size = ctx->log_size;
void *ptr;
 
if (!ctx->log) {
log_size = 65536;
-   } else {
+   } else if (log_size < log_max) {
log_size <<= 1;
-   if (log_size > (UINT_MAX >> 8))
-   return -EINVAL;
+   if (log_size > log_max)
+   log_size = log_max;
+   } else {
+   return -EINVAL;
}
 
ptr = realloc(ctx->log, log_size);
@@ -1259,7 +1262,7 @@ retry:
 * log for the user, so enlarge it and re-fail.
 */
if (fd < 0 && (errno == ENOSPC || !ctx->log_size)) {
-   if (tries++ < 6 && !bpf_log_realloc(ctx))
+   if (tries++ < 10 && !bpf_log_realloc(ctx))
goto retry;
 
fprintf(stderr, "Log buffer too small to dump verifier 
log %zu bytes (%d tries)!\n",
-- 
2.7.4