ss: fix crash when skipping disabled header field

When the first header field is disabled (i.e. when passing the -t
option), field_flush() is invoked with the `buffer` global variable
still zero'd.
However, in field_flush() we try to access buffer.cur->len
during variables initialization, thus leading to a SIGSEGV.

It's interesting to note that this bug appears only when the code
is compiled with -O0, because the compiler is smart
enough to immediately jump to the return statement if optimizations
are enabled and skip the faulty instruction.

Cc: Stefano Brivio <sbrivio@redhat.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>

diff --git a/misc/ss.c b/misc/ss.c
index 1abf43d08091a9fd1f42e4b186105747a384a2f3..b35859dc40442778e2480ea043ad650bafaa2957 100644 (file)
--- a/misc/ss.c
+++ b/misc/ss.c
@@ -1018,12 +1018,15 @@ static void print_right_spacing(struct column *f, int printed)
 /* Done with field: update buffer pointer, start new token after current one */
 static void field_flush(struct column *f)
 {
-       struct buf_chunk *chunk = buffer.tail;
-       unsigned int pad = buffer.cur->len % 2;
+       struct buf_chunk *chunk;
+       unsigned int pad;
 
        if (f->disabled)
                return;
 
+       chunk = buffer.tail;
+       pad = buffer.cur->len % 2;
+
        if (buffer.cur->len > f->max_len)
                f->max_len = buffer.cur->len;