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Date: Sat, 12 Mar 2022 18:25:28 -0500 From: Steven Rostedt <rostedt@...dmis.org> To: linux-kernel@...r.kernel.org Cc: Ingo Molnar <mingo@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, kernel test robot <lkp@...el.com> Subject: [for-next][PATCH 03/12] tracing: Fix last_cmd_set() string management in histogram code From: "Steven Rostedt (Google)" <rostedt@...dmis.org> Using strnlen(dest, str, n) is confusing, as the size of dest must be strlen(dest) + n + 1. Even more confusing, using sizeof(string constant) gives you strlen(string constant) + 1 and not just strlen(). These two together made using strncat() with a constant string a bit off in the calculations as we have: len = sizeof(HIST_PREFIX) + strlen(str) + 1; kfree(last_cmd); last_cmd = kzalloc(len, GFP_KERNEL); strcpy(last_cmd, HIST_PREFIX); len -= sizeof(HIST_PREFIX) + 1; strncat(last_cmd, str, len); The above works if we s/sizeof/strlen/ with HIST_PREFIX (which is defined as "hist:", but because sizeof(HIST_PREFIX) is equal to strlen(HIST_PREFIX) + 1, we can drop the +1 in the code. But at least comment that we are doing so. Link: https://lore.kernel.org/all/202203082112.Iu7tvFl4-lkp@intel.com/ Fixes: 9f8e5aee93ed2 ("tracing: Fix allocation of last_cmd in last_cmd_set()") Reported-by: kernel test robot <lkp@...el.com> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org> --- kernel/trace/trace_events_hist.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 78788049f3d3..954b19e2f196 100644 --- a/kernel/trace/trace_events_hist.c +++ b/kernel/trace/trace_events_hist.c @@ -749,14 +749,16 @@ static void last_cmd_set(struct trace_event_file *file, char *str) if (!str) return; - len = sizeof(HIST_PREFIX) + strlen(str) + 1; + /* sizeof() contains the nul byte */ + len = sizeof(HIST_PREFIX) + strlen(str); kfree(last_cmd); last_cmd = kzalloc(len, GFP_KERNEL); if (!last_cmd) return; strcpy(last_cmd, HIST_PREFIX); - len -= sizeof(HIST_PREFIX) + 1; + /* Again, sizeof() contains the nul byte */ + len -= sizeof(HIST_PREFIX); strncat(last_cmd, str, len); if (file) { -- 2.35.1
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