[PATCH 6/7] Handle snprintf truncation in msm_perf more gracefully

[Eric Sesterhenn]

This prevents the snprintf to cause a WARN_ON_ONCE if
rem gets negative. This can happen if an earlier snprintf
truncates the string but returns the length it would require
to print the full string.

Signed-off-by: Eric Sesterhenn <eric.sesterh...@x41-dsec.de>
---
 drivers/gpu/drm/msm/msm_perf.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_perf.c b/drivers/gpu/drm/msm/msm_perf.c
index 5ab21bd2decb..93803ca869d5 100644
--- a/drivers/gpu/drm/msm/msm_perf.c
+++ b/drivers/gpu/drm/msm/msm_perf.c
@@ -77,7 +77,7 @@ static int refill_buf(struct msm_perf_state *perf)
                ptr += n;
                rem -= n;

-               for (i = 0; i < gpu->num_perfcntrs; i++) {
+               for (i = 0; i < gpu->num_perfcntrs && rem > 0; i++) {
                        const struct msm_gpu_perfcntr *perfcntr = 
&gpu->perfcntrs[i];
                        n = snprintf(ptr, rem, "\t%s", perfcntr->name);
                        ptr += n;
@@ -105,7 +105,7 @@ static int refill_buf(struct msm_perf_state *perf)
                ptr += n;
                rem -= n;

-               for (i = 0; i < ret; i++) {
+               for (i = 0; i < ret && rem > 0; i++) {
                        /* cycle counters (I think).. convert to MHz.. */
                        val = cntrs[i] / 10000;
                        n = snprintf(ptr, rem, "\t%5d.%02d",
@@ -115,9 +115,11 @@ static int refill_buf(struct msm_perf_state *perf)
                }
        }

-       n = snprintf(ptr, rem, "\n");
-       ptr += n;
-       rem -= n;
+       if (rem > 0) {
+               n = snprintf(ptr, rem, "\n");
+               ptr += n;
+               rem -= n;
+       }

        perf->bufpos = 0;
        perf->buftot = ptr - perf->buf;
-- 
Eric Sesterhenn (Principal Security Consultant)
X41 D-SEC GmbH, Dennewartstr. 25-27, D-52068 Aachen
T: +49 241 9809418-0, Fax: -9
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