I just found out that if an application opens a shared library (both built with address sanitizer) using RTLD_DEEPBIND, address sanitizer will fail to intercept the functions called from the so opened shared library. In my particular case, this manifested itself as a strdup which, though originally skipping any interceptors and going into libc, would eventually call asan's allocator. However the same did not happen for free (since it went straight into glibc's free), so it failed to intercept free (or rather there was an allocator mismatch). I am not familiar enough with glibc to say whether this can be fixed or not, but perhaps we could drop the RTLD_DEEPBIND flag in our dlopen interceptor and issue a warning to the user.