From: Andreas Ziegler andreas.ziegler@fau.de
commit 0722069a5374b904ec1a67f91249f90e1cfae259 upstream.
When printing multiple uprobe arguments as strings the output for the earlier arguments would also include all later string arguments.
This is best explained in an example:
Consider adding a uprobe to a function receiving two strings as parameters which is at offset 0xa0 in strlib.so and we want to print both parameters when the uprobe is hit (on x86_64):
$ echo 'p:func /lib/strlib.so:0xa0 +0(%di):string +0(%si):string' > \ /sys/kernel/debug/tracing/uprobe_events
When the function is called as func("foo", "bar") and we hit the probe, the trace file shows a line like the following:
[...] func: (0x7f7e683706a0) arg1="foobar" arg2="bar"
Note the extra "bar" printed as part of arg1. This behaviour stacks up for additional string arguments.
The strings are stored in a dynamically growing part of the uprobe buffer by fetch_store_string() after copying them from userspace via strncpy_from_user(). The return value of strncpy_from_user() is then directly used as the required size for the string. However, this does not take the terminating null byte into account as the documentation for strncpy_from_user() cleary states that it "[...] returns the length of the string (not including the trailing NUL)" even though the null byte will be copied to the destination.
Therefore, subsequent calls to fetch_store_string() will overwrite the terminating null byte of the most recently fetched string with the first character of the current string, leading to the "accumulation" of strings in earlier arguments in the output.
Fix this by incrementing the return value of strncpy_from_user() by one if we did not hit the maximum buffer size.
Link: http://lkml.kernel.org/r/20190116141629.5752-1-andreas.ziegler@fau.de
Cc: Ingo Molnar mingo@redhat.com Cc: stable@vger.kernel.org Fixes: 5baaa59ef09e ("tracing/probes: Implement 'memory' fetch method for uprobes") 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 Signed-off-by: Masami Hiramatsu mhiramat@kernel.org --- kernel/trace/trace_uprobe.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c index a4c3219ec62d..83b6eaf924ed 100644 --- a/kernel/trace/trace_uprobe.c +++ b/kernel/trace/trace_uprobe.c @@ -151,6 +151,13 @@ static void FETCH_FUNC_NAME(memory, string)(struct pt_regs *regs, ret = strncpy_from_user(dst, src, maxlen); if (ret == maxlen) dst[--ret] = '\0'; + else if (ret >= 0) + /* + * Include the terminating null byte. In this case it + * was copied by strncpy_from_user but not accounted + * for in ret. + */ + ret++;
if (ret < 0) { /* Failed to fetch string */ ((u8 *)get_rloc_data(dest))[0] = '\0';