On Wed, 9 Jun 2021 14:43:51 -0700 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Jun 9, 2021 at 1:52 PM Steven Rostedt <rostedt@xxxxxxxxxxx> 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
