From: Steven Rostedt rostedt@goodmis.org
The filter string testing uses strncpy_from_kernel/user_nofault() to retrieve the string to test the filter against. The if() statement was incorrect as it considered 0 as a fault, when it is only negative that it faulted.
Running the following commands:
# cd /sys/kernel/tracing # echo "filename.ustring ~ "/proc*"" > events/syscalls/sys_enter_openat/filter # echo 1 > events/syscalls/sys_enter_openat/enable # ls /proc/$$/maps # cat trace
Would produce nothing, but with the fix it will produce something like:
ls-1192 [007] ..... 8169.828333: sys_openat(dfd: ffffffffffffff9c, filename: 7efc18359904, flags: 80000, mode: 0)
Link: https://lore.kernel.org/all/CAEf4BzbVPQ=BjWztmEwBPRKHUwNfKBkS3kce-Rzka6zvbQe...
Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Andrew Morton akpm@linux-foundation.org Link: https://lore.kernel.org/20250417183003.505835fb@gandalf.local.home Fixes: 77360f9bbc7e5 ("tracing: Add test for user space strings when filtering on string pointers") Reported-by: Andrii Nakryiko andrii.nakryiko@gmail.com Reported-by: Mykyta Yatsenko mykyta.yatsenko5@gmail.com Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/trace_events_filter.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index 0993dfc1c5c1..2048560264bb 100644 --- a/kernel/trace/trace_events_filter.c +++ b/kernel/trace/trace_events_filter.c @@ -808,7 +808,7 @@ static __always_inline char *test_string(char *str) kstr = ubuf->buffer;
/* For safety, do not trust the string pointer */ - if (!strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE)) + if (strncpy_from_kernel_nofault(kstr, str, USTRING_BUF_SIZE) < 0) return NULL; return kstr; } @@ -827,7 +827,7 @@ static __always_inline char *test_ustring(char *str)
/* user space address? */ ustr = (char __user *)str; - if (!strncpy_from_user_nofault(kstr, ustr, USTRING_BUF_SIZE)) + if (strncpy_from_user_nofault(kstr, ustr, USTRING_BUF_SIZE) < 0) return NULL;
return kstr;