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tracing: probeevent: Correctly update remaining space in dynamic area
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Commit 9178412 ("tracing: probeevent: Return consumed
bytes of dynamic area") improved the string fetching
mechanism by returning the number of required bytes after
copying the argument to the dynamic area. However, this
return value is now only used to increment the pointer
inside the dynamic area but misses updating the 'maxlen'
variable which indicates the remaining space in the dynamic
area.

This means that fetch_store_string() always reads the *total*
size of the dynamic area from the data_loc pointer instead of
the *remaining* size (and passes it along to
strncpy_from_{user,unsafe}) even if we're already about to
copy data into the middle of the dynamic area.

Link: http://lkml.kernel.org/r/20190206190013.16405-1-andreas.ziegler@fau.de

Cc: Ingo Molnar <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 9178412 ("tracing: probeevent: Return consumed bytes of dynamic area")
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Andreas Ziegler <andreas.ziegler@fau.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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Andreas Ziegler authored and Steven Rostedt (VMware) committed Feb 11, 2019
1 parent 0722069 commit f667587
Showing 1 changed file with 4 additions and 2 deletions.
6 changes: 4 additions & 2 deletions kernel/trace/trace_probe_tmpl.h
Original file line number Diff line number Diff line change
Expand Up @@ -180,10 +180,12 @@ store_trace_args(void *data, struct trace_probe *tp, struct pt_regs *regs,
if (unlikely(arg->dynamic))
*dl = make_data_loc(maxlen, dyndata - base);
ret = process_fetch_insn(arg->code, regs, dl, base);
if (unlikely(ret < 0 && arg->dynamic))
if (unlikely(ret < 0 && arg->dynamic)) {
*dl = make_data_loc(0, dyndata - base);
else
} else {
dyndata += ret;
maxlen -= ret;
}
}
}

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