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-rw-r--r--kernel/trace/bpf_trace.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 5113fd423cdf..048c655315f1 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -181,6 +181,16 @@ bpf_probe_read_user_str_common(void *dst, u32 size,
{
int ret;
+ /*
+ * NB: We rely on strncpy_from_user() not copying junk past the NUL
+ * terminator into `dst`.
+ *
+ * strncpy_from_user() does long-sized strides in the fast path. If the
+ * strncpy does not mask out the bytes after the NUL in `unsafe_ptr`,
+ * then there could be junk after the NUL in `dst`. If user takes `dst`
+ * and keys a hash map with it, then semantically identical strings can
+ * occupy multiple entries in the map.
+ */
ret = strncpy_from_user_nofault(dst, unsafe_ptr, size);
if (unlikely(ret < 0))
memset(dst, 0, size);