Messages in this thread | | | Date | Wed, 9 Jun 2021 18:18:55 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] tracing: Correct the length check which causes memory corruption |
| |
On Wed, 9 Jun 2021 14:43:51 -0700 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Wed, Jun 9, 2021 at 1:52 PM Steven Rostedt <rostedt@goodmis.org> wrote: > > > > > > That "sizeof(*entry)" is clearly wrong, because it doesn't take the > > > unsized array into account. > > > > Correct. That's because I forgot that the structure has that empty array :-( > > Note that 'sparse' does have the option to warn about odd flexible > array uses. Including 'sizeof()'. > > You can do something like > > CF='-Wflexible-array-sizeof' make C=2 kernel/trace/trace.o > > and you'll see > > kernel/trace/trace.c:1022:17: warning: using sizeof on a flexible structure
alloc = sizeof(*entry) + size + 2; /* possible \n added */
Entry is created via a macro. But I guess that too could use a struct_size().
> kernel/trace/trace.c:2645:17: warning: using sizeof on a flexible structure
memset(event, 0, sizeof(*event));
Hah, this is the part that is clearing the first part of the ring_buffer_event structure of that temp buffer. Where it's setting "type_len" to zero. It doesn't care about the extended portion here.
> kernel/trace/trace.c:2739:41: warning: using sizeof on a flexible structure
This is the code we are talking about now.
> kernel/trace/trace.c:3290:16: warning: using sizeof on a flexible structure
This is like the first one. A macro created the structure, but probably could be switched over.
> kernel/trace/trace.c:3350:16: warning: using sizeof on a flexible structure
Same as the first occurrence.
> kernel/trace/trace.c:6989:16: warning: using sizeof on a flexible structure
Also the same as the first.
> kernel/trace/trace.c:7070:16: warning: using sizeof on a flexible structure
And same as the first.
> > and I suspect every single one of those should be using > 'struct_size()' instead for a sizeof() on the base structure plus some > manual arithmetic (or, as in the case of this bug, _without_ the extra > arithmetic).
Most of the above are for structures that hold dynamic size strings. But I have no problem converting them to struct_size. But since they are created by FTRACE_ENTRY*() macros in kernel/trace/trace_entries.h, we need to be careful in picking the field to use.
> > And yeah, it isn't just the tracing code that does this. We have it > all over, so that sparse check isn't on by default. Sparse is pretty > darn noisy even without it, but it can be worth using that > CF='-Wflexible-array-sizeof' on individual files that you want to > check.
Could be a task for an intern to do?
-- Steve
| |