Add --save-smaller|-U to keep smallest duplicate

While --save_all can be used to save all crashes, often people only
really want to find the smallest possible crash file.

This patch adds a --save_smaller option that overwrites the crash file
when it would shrink the file size.

See google#305

cmdline.c

@@ -322,6 +322,7 @@ bool cmdlineParse(int argc, char* argv[], honggfuzz_t* hfuzz) {
                 .crashDir         = NULL,
                 .covDirNew        = NULL,
                 .saveUnique       = true,
+                .saveSmaller      = false,
                 .dynfileqMaxSz    = 0U,
                 .dynfileqCnt      = 0U,
                 .dynfileqCurrent  = NULL,
@@ -508,6 +509,7 @@ bool cmdlineParse(int argc, char* argv[], honggfuzz_t* hfuzz) {
         { { "clear_env", no_argument, NULL, 0x108 }, "Clear all environment variables before executing the binary" },
         { { "env", required_argument, NULL, 'E' }, "Pass this environment variable, can be used multiple times" },
         { { "save_all", no_argument, NULL, 'u' }, "Save all test-cases (not only the unique ones) by appending the current time-stamp to the filenames" },
+        { { "save_smaller", no_argument, NULL, 'U' }, "Save smaller test-cases, renaming first filename with .orig suffix" },
         { { "tmout_sigvtalrm", no_argument, NULL, 'T' }, "Treat time-outs as crashes - use SIGVTALRM to kill timeouting processes (default: use SIGKILL)" },
         { { "sanitizers", no_argument, NULL, 'S' }, "** DEPRECATED ** Enable sanitizers settings (default: false)" },
         { { "sanitizers_del_report", required_argument, NULL, 0x10F }, "Delete sanitizer report after use (default: false)" },
@@ -555,7 +557,7 @@ bool cmdlineParse(int argc, char* argv[], honggfuzz_t* hfuzz) {
     int           opt_index = 0;
     for (;;) {
         int c = getopt_long(
-            argc, argv, "-?hQvVsuPxf:i:o:dqe:W:r:c:F:t:R:n:N:l:p:g:E:w:B:zMTS", opts, &opt_index);
+            argc, argv, "-?hQvVsuUPxf:i:o:dqe:W:r:c:F:t:R:n:N:l:p:g:E:w:B:zMTS", opts, &opt_index);
         if (c < 0) {
             break;
         }
@@ -587,6 +589,9 @@ bool cmdlineParse(int argc, char* argv[], honggfuzz_t* hfuzz) {
             case 'u':
                 hfuzz->io.saveUnique = false;
                 break;
+            case 'U':
+                hfuzz->io.saveSmaller = true;
+                break;
             case 'l':
                 logfile = optarg;
                 break;

docs/USAGE.md

@@ -179,6 +179,8 @@ Options:
 	Pass this environment variable, can be used multiple times
  --save_all|-u 
 	Save all test-cases (not only the unique ones) by appending the current time-stamp to the filenames
+ --save_smaller|-U
+    Save smaller test-cases, renaming first found with .orig suffix
  --tmout_sigvtalrm|-T 
 	Use SIGVTALRM to kill timeouting processes (default: use SIGKILL)
  --sanitizers|-S 

honggfuzz.h

@@ -208,6 +208,7 @@ typedef struct {
         const char* crashDir;
         const char* covDirNew;
         bool        saveUnique;
+        bool        saveSmaller;
         size_t      dynfileqMaxSz;
         size_t      dynfileqCnt;
         dynfile_t*  dynfileqCurrent;

linux/trace.c

@@ -703,10 +703,39 @@ static void arch_traceSaveData(run_t* run, pid_t pid) {
     }
 
     if (files_exists(run->crashFileName)) {
-        LOG_I("Crash (dup): '%s' already exists, skipping", run->crashFileName);
-        /* Clear filename so that verifier can understand we hit a duplicate */
-        memset(run->crashFileName, 0, sizeof(run->crashFileName));
-        return;
+        if (run->global->io.saveSmaller) {
+            /*
+             * If the new run produces a smaller file than exists already, we
+             * will replace it.
+             *
+             * If this is the second test case, we save the first with .orig
+             * suffix before overwriting.
+             */
+            struct stat st;
+            char origFile[PATH_MAX];
+            if (stat(run->crashFileName, &st) == -1) {
+                LOG_W("Couldn't stat() the '%s' file", run->crashFileName);
+            } else if (st.st_size <= (off_t)run->dynfile->size) {
+                LOG_I("Crash (dup): '%s' exists and is smaller, skipping", run->crashFileName);
+                /* Clear filename so that verifier can understand we hit a duplicate */
+                memset(run->crashFileName, 0, sizeof(run->crashFileName));
+                return;
+            } else {
+                /* we have a new champion */
+                LOG_I("Crash: overwriting '%s' (old %zu bytes, new %zu bytes)",
+                      run->crashFileName, (size_t)st.st_size, (size_t)run->dynfile->size);
+            }
+
+            snprintf(origFile, sizeof(origFile), "%s.orig", run->crashFileName);
+            if (! files_exists(origFile)) {
+                rename(run->crashFileName, origFile);
+            }
+        } else {
+            LOG_I("Crash (dup): '%s' already exists, skipping", run->crashFileName);
+            /* Clear filename so that verifier can understand we hit a duplicate */
+            memset(run->crashFileName, 0, sizeof(run->crashFileName));
+            return;
+        }
     }
 
     if (!files_writeBufToFile(run->crashFileName, run->dynfile->data, run->dynfile->size,