From 81b49e969233ac5b9faf5c043bb0cc64bf9d6271 Mon Sep 17 00:00:00 2001 From: Tulio Magno Quites Machado Filho Date: Thu, 26 Apr 2018 10:41:43 -0300 Subject: Increase robustness of internal dlopen() by using RTLD_NOW [BZ #22766] Prevent random runtime crashes due to missing symbols caused by mixed libnss_* versions. [BZ #22766] * include/dlfcn.h [__libc_dl_open]: Replace RTLD_LAZY with RTLD_NOW. * sysdeps/gnu/unwind-resume.c (__lib_gcc_s_init): Replace __libc_dlopen_mode() using RTLD_NOW with __libc_dlopen. * sysdeps/nptl/unwind-forcedunwind.c: Likewise. Signed-off-by: Tulio Magno Quites Machado Filho Reviewed-by: Carlos O'Donell --- include/dlfcn.h | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) (limited to 'include') diff --git a/include/dlfcn.h b/include/dlfcn.h index 12ef913e19..694e71c83b 100644 --- a/include/dlfcn.h +++ b/include/dlfcn.h @@ -31,8 +31,29 @@ extern char **__libc_argv attribute_hidden; /* Now define the internal interfaces. */ +/* Use RTLD_NOW here because: + 1. In pthread_cancel_init we want to use RTLD_NOW to reduce the stack usage + of future cancellation operations, particularly when the target thread + is running with a small stack. Likewise for consistency we do the same + thing in __libgcc_s_init. RTLD_NOW will rarely make a difference for + __libgcc_s_init because unwinding is already in progress, so libgcc_s.so + has already been loaded if its unwinder is used (Bug 22636). + 2. It allows us to provide robust fallback code at dlopen time for + incorrectly configured systems that mix old libnss_* modules with newly + installed libraries e.g. old libnss_nis.so.2 with new libnsl.so.1. Using + RTLD_LAZY here causes a failure at the time the symbol is called and at + that point it is much harder to safely return an error (Bug 22766). + + The use of RTLD_NOW also impacts gconv module loading, backtracing + (where the unwinder form libgcc_s.so is used), and IDNA functions + (which load libidn), all of which load their respective DSOs on + demand, and so should not impact program startup. That is to say + that the DSOs are loaded as part of an API call and therefore we + will be calling that family of API functions shortly so RTLD_NOW or + RTLD_LAZY is not a big difference in performance, but RTLD_NOW has + better error handling semantics for the library. */ #define __libc_dlopen(name) \ - __libc_dlopen_mode (name, RTLD_LAZY | __RTLD_DLOPEN) + __libc_dlopen_mode (name, RTLD_NOW | __RTLD_DLOPEN) extern void *__libc_dlopen_mode (const char *__name, int __mode); extern void *__libc_dlsym (void *__map, const char *__name); extern void *__libc_dlvsym (void *map, const char *name, const char *version); -- cgit v1.2.3