Re: [Crash-utility] freeing of uninitialised variable in reg_callback()

Yes - that problem was introduced (left behind) from the prior fix to unload. That is the right fix. Thanks Lachlan. -----Original Message----- From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf Of Lachlan McIlroy Sent: Tuesday, January 03, 2012 7:31 PM To: crash-utility(a)redhat.com Subject: [Crash-utility] freeing of uninitialised variable in reg_callback() I'm using crash 6.0.2 and I'm regularly seeing this segfault from sial when unloading a sial script: crash> extend ./sial.so Core LINUX_RELEASE == '2.6.18-238.12.1.el5' < Sial interpreter version 3.0 > Loading sial commands from /usr/share/sial/crash:/home/lmcilroy/.sial .... Done. ./sial.so: shared object loaded crash> load script.sial crash> unload script.sial *** glibc detected *** crash: double free or corruption (!prev): 0x00000000071999b0 *** Segmentation fault Program received signal SIGSEGV, Segmentation fault. 0x0000003b61c74f32 in malloc_consolidate () from /lib64/libc.so.6 (gdb) bt #0 0x0000003b61c74f32 in malloc_consolidate () from /lib64/libc.so.6 #1 0x0000003b61c77bd2 in _int_malloc () from /lib64/libc.so.6 #2 0x0000003b61c78c88 in calloc () from /lib64/libc.so.6 #3 0x0000003b6180a98f in _dl_new_object () from /lib64/ld-linux-x86-64.so.2 #4 0x0000003b61805e4f in _dl_map_object_from_fd () from /lib64/ld-linux-x86-64.so.2 #5 0x0000003b61807bd2 in _dl_map_object () from /lib64/ld-linux-x86-64.so.2 #6 0x0000003b61812530 in dl_open_worker () from /lib64/ld-linux-x86-64.so.2 #7 0x0000003b6180dd76 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2 #8 0x0000003b61811fb7 in _dl_open () from /lib64/ld-linux-x86-64.so.2 #9 0x0000003b61d1afb0 in do_dlopen () from /lib64/libc.so.6 #10 0x0000003b6180dd76 in _dl_catch_error () from /lib64/ld-linux-x86-64.so.2 #11 0x0000003b61d1b107 in __libc_dlopen_mode () from /lib64/libc.so.6 #12 0x0000003b61cf3cc1 in backtrace () from /lib64/libc.so.6 #13 0x0000003b61c6f147 in __libc_message () from /lib64/libc.so.6 #14 0x0000003b61c74ac6 in malloc_printerr () from /lib64/libc.so.6 #15 0x00007f85babefe7a in sial_deletefile (name=0x462bf78 "script.sial") at sial_func.c:320 #16 0x00007f85babf5d36 in sial_loadunload (load=0, name=<value optimized out>, silent=0) at sial_api.c:1289 #17 0x00007f85babec77d in unload_cmd () at sial.c:775 #18 0x000000000045d4df in exec_command () at main.c:751 #19 0x000000000045d6ea in main_loop () at main.c:699 #20 0x0000000000557019 in captured_command_loop (data=<value optimized out>) at ./main.c:228 #21 0x00000000005552eb in catch_errors (func=<value optimized out>, func_args=<value optimized out>, errstring=<value optimized out>, mask=<value optimized out>) at exceptions.c:531 #22 0x0000000000556d26 in captured_main (data=<value optimized out>) at ./main.c:958 #23 0x00000000005552eb in catch_errors (func=<value optimized out>, func_args=<value optimized out>, errstring=<value optimized out>, mask=<value optimized out>) at exceptions.c:531 #24 0x0000000000555ee4 in gdb_main (args=0x98) at ./main.c:973 #25 0x0000000000555f1e in gdb_main_entry (argc=<value optimized out>, argv=<value optimized out>) at ./main.c:993 #26 0x000000000045e24f in main (argc=<value optimized out>, argv=<value optimized out>) at main.c:603 I've traced the fault to extensions/sial.c:reg_callback() where it is freeing 'help_str' without it being initialised first. void reg_callback(char *name, int load) { char fname[MAX_SYMNAMELEN+sizeof("_usage")+1]; char *help_str, *opt_str; char **help=malloc(sizeof *help * 5); if(!help) return; snprintf(fname, sizeof(fname), "%s_help", name); if(sial_chkfname(fname, 0)) { snprintf(fname, sizeof(fname), "%s_usage", name); if(sial_chkfname(fname, 0)) { if(load) { opt_str=sial_strdup((char*)(unsigned long)sial_exefunc(fname, 0)); snprintf(fname, sizeof(fname), "%s_help", name); help_str=sial_strdup((char*)(unsigned long)sial_exefunc(fname, 0)); help[0]=sial_strdup(name); help[1]=""; help[2]=sial_strdup(opt_str); help[3]=sial_strdup(help_str); help[4]=0; add_sial_cmd(name, run_callback, help, 0); sial_free(help_str); sial_free(opt_str); return; } else rm_sial_cmd(name); } sial_free(help_str); <--- segfaults here. } free(help); return; } I don't see how 'help_str' should be initialised at this point and removing the 'sial_free(help_str)' prevents the problem - is that the right thing to do here? Lachlan -- Crash-utility mailing list Crash-utility(a)redhat.com https://www.redhat.com/mailman/listinfo/crash-utility