Messages in this thread | | | Date | Tue, 8 Dec 2020 12:53:40 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH v3 3/5] tracing: Update synth command errors |
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On Tue, 08 Dec 2020 11:34:41 -0600 Tom Zanussi <zanussi@kernel.org> wrote:
> Unfortunately, you're correct, if you have a script that creates a > synthetic event without semicolons, this patchset will break it, as I > myself found out and fixed in patch 4 ([PATCH v3 4/5] selftests/ftrace: > Add synthetic event field separators) [4]. > > So whereas before this would work, even though it shouldn't have in the > first place: > > # echo 'wakeup_latency u64 lat pid_t pid char comm[16]' > > synthetic_events > > it now has to be: > > # echo 'wakeup_latency u64 lat; pid_t pid; char comm[16]' > > synthetic_events > > So yeah, this patchset fixes a set of parsing bugs for things that > shouldn't have been accepted as valid, but shouldn't break things that > are obviously valid. > > If it's too late to fix them, though, I guess we'll just have to live > with them, or some other option?
I would suggest allowing the old interface work (with no new features, for backward compatibility), but new things like "char comm[16]" we require semicolons.
One method to do this is to add to the start of reading the string, and checking if it has semicolons. If it does not, we create a new string with them, but make sure that the string does not include new changes.
strncpy_from_user(buffer, user_buff, sizeof(buffer));
if (!strstr(buffer, ";")) { if (!audit_old_buffer(buffer)) goto error; insert_colons(buffer); }
That is, if the buffer does not have semicolons, then check if it is a valid "old format", and if not, we error out. Otherwise, we insert the colons into the buffer, and process that as if the user put in colons:
That is:
echo 'wakeup_latency u64 lat pid_t pid' > synthetic_events
would change the buffer to:
"wakeup_latency u64 lat; pid_t pid;"
And then put it through the normal processing. I think its OK that if the user were to cat out the synthetic events, it would see the semicolons even if it did not add them. As I don't think that will break userspace.
Does that make sense?
-- Steve
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