Messages in this thread | | | Subject | Re: [PATCH] trace-cmd: prevent print_graph_duration buffer overflow | From | Chase Douglas <> | Date | Sun, 13 Jun 2010 17:01:34 -0400 |
| |
On Sun, 2010-06-13 at 16:52 -0400, Valdis.Kletnieks@vt.edu wrote: > On Sun, 13 Jun 2010 13:11:48 EDT, Chase Douglas said: > > Passing n > sizeof(string) to snprintf can cause a glibc buffer overflow > > condition. We know the exact size of nsecs_str, so use it instead of > > math that may overflow. > > > /* Print nsecs (we don't want to exceed 7 numbers) */ > > if ((s->len - len) < 7) { > > - snprintf(nsecs_str, 8 - (s->len - len), "%03lu", nsecs_rem); > > + snprintf(nsecs_str, sizeof(nsecs_str), "%03lu", nsecs_rem); > > We only get into this code after we've checked that the length is under 7 > characters. How much overflow can happen as long as the sizeof(nsecs_str) is a > sane size (like at least 8 chars)? Probably a better bet would be doing the > right thing and 'BUILD_BUG_ON(sizeof(nsecs_str) < 8);'?
nsecs_str is a local variable defined just above this block of code as:
char nsecs_str[5];
I was hitting cases where s->len == 64 and len == 63, leading to the size argument of snprintf being 7 on a 5 byte string. I didn't delve too much into the reasoning for the if statement, but I think it's math is not actually related to the size of nsecs_rem but to some other string length.
-- Chase
| |