tracing: Handle %.*s in trace_check_vprintf()

If a trace event uses the %*.s notation, the trace_check_vprintf() will
fail and will warn about a bad processing of strings, because it does not
take into account the length field when processing the star (*) part.
Have it handle this case as well.

Link: https://lore.kernel.org/linux-nfs/238C0E2D-C2A4-4578-ADD2-C565B3B99842@oracle.com/
Reported-by: Chuck Lever III <chuck.lever@oracle.com>
Fixes: 9a6944fee68e2 ("tracing: Add a verifier to check string pointers for trace events")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 560e4c8..a21ef9c 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3704,6 +3704,9 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
                goto print;
 
        while (*p) {
+               bool star = false;
+               int len = 0;
+
                j = 0;
 
                /* We only care about %s and variants */
@@ -3725,13 +3728,17 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
                                /* Need to test cases like %08.*s */
                                for (j = 1; p[i+j]; j++) {
                                        if (isdigit(p[i+j]) ||
-                                           p[i+j] == '*' ||
                                            p[i+j] == '.')
                                                continue;
+                                       if (p[i+j] == '*') {
+                                               star = true;
+                                               continue;
+                                       }
                                        break;
                                }
                                if (p[i+j] == 's')
                                        break;
+                               star = false;
                        }
                        j = 0;
                }
@@ -3744,6 +3751,9 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
                iter->fmt[i] = '\0';
                trace_seq_vprintf(&iter->seq, iter->fmt, ap);
 
+               if (star)
+                       len = va_arg(ap, int);
+
                /* The ap now points to the string data of the %s */
                str = va_arg(ap, const char *);
 
@@ -3762,8 +3772,18 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
                        int ret;
 
                        /* Try to safely read the string */
-                       ret = strncpy_from_kernel_nofault(iter->fmt, str,
-                                                         iter->fmt_size);
+                       if (star) {
+                               if (len + 1 > iter->fmt_size)
+                                       len = iter->fmt_size - 1;
+                               if (len < 0)
+                                       len = 0;
+                               ret = copy_from_kernel_nofault(iter->fmt, str, len);
+                               iter->fmt[len] = 0;
+                               star = false;
+                       } else {
+                               ret = strncpy_from_kernel_nofault(iter->fmt, str,
+                                                                 iter->fmt_size);
+                       }
                        if (ret < 0)
                                trace_seq_printf(&iter->seq, "(0x%px)", str);
                        else
@@ -3775,7 +3795,10 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
                        strncpy(iter->fmt, p + i, j + 1);
                        iter->fmt[j+1] = '\0';
                }
-               trace_seq_printf(&iter->seq, iter->fmt, str);
+               if (star)
+                       trace_seq_printf(&iter->seq, iter->fmt, len, str);
+               else
+                       trace_seq_printf(&iter->seq, iter->fmt, str);
 
                p += i + j + 1;
        }