From: Steven Rostedt (Google) Date: Tue, 8 Mar 2022 15:39:45 +0000 (-0500) Subject: tracing: Fix last_cmd_set() string management in histogram code X-Git-Tag: v6.1-rc5~1772^2~11 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=5677a3d713ad795e3ce32d631941e982777b43db;p=platform%2Fkernel%2Flinux-starfive.git tracing: Fix last_cmd_set() string management in histogram code 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 Signed-off-by: Steven Rostedt (Google) --- diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c index 7878804..954b19e 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) {