From 288dc1d8eeb3340068792698e98960c59faa6c99 Mon Sep 17 00:00:00 2001 From: Willy Tarreau Date: Sat, 16 Jul 2022 13:49:34 +0200 Subject: [PATCH] BUG/MEDIUM: tools: avoid calling dlsym() in static builds Since 2.4 with commit 64192392c ("MINOR: tools: add functions to retrieve the address of a symbol"), we can resolve symbols. However some old glibc crash in dlsym() when the program is statically built. Fortunately even on these old libs we can detect lack of support by calling dlopen(NULL). Normally it returns a handle to the current program, but on a static build it returns NULL. This is sufficient to refrain from calling dlsym() (which will be of very limited use anyway), so we check this once at boot and use the result when needed. This may be backported to 2.4. On stable versions, be careful to place the init code inside an if/endif guard that checks for DL support. --- src/tools.c | 23 +++++++++++++++++++++-- 1 file changed, 21 insertions(+), 2 deletions(-) diff --git a/src/tools.c b/src/tools.c index e77b7e13bb..44424176cc 100644 --- a/src/tools.c +++ b/src/tools.c @@ -4920,6 +4920,23 @@ static int dladdr_and_size(const void *addr, Dl_info *dli, size_t *size) return ret; } +/* dlopen() support: 0=no/not yet checked, 1=ok */ +static int dlopen_usable = 0; + +/* Sets dlopen_usable to true if dlopen() works and is usable. We verify if + * we're in a static build because some old glibcs used to crash in dlsym() + * in this case. + */ +void check_if_dlopen_usable() +{ + /* dlopen(NULL) returns a handle to the main program or NULL + * on static builds. + */ + dlopen_usable = dlopen(NULL, RTLD_LAZY) ? 1 : 0; +} + +INITCALL0(STG_PREPARE, check_if_dlopen_usable); + /* Tries to retrieve the address of the first occurrence symbol . * Note that NULL in return is not always an error as a symbol may have that * address in special situations. @@ -4929,7 +4946,8 @@ void *get_sym_curr_addr(const char *name) void *ptr = NULL; #ifdef RTLD_DEFAULT - ptr = dlsym(RTLD_DEFAULT, name); + if (dlopen_usable) + ptr = dlsym(RTLD_DEFAULT, name); #endif return ptr; } @@ -4944,7 +4962,8 @@ void *get_sym_next_addr(const char *name) void *ptr = NULL; #ifdef RTLD_NEXT - ptr = dlsym(RTLD_NEXT, name); + if (dlopen_usable) + ptr = dlsym(RTLD_NEXT, name); #endif return ptr; } -- 2.39.5