override - Overriding getdirentries in C -
i override getdirentries (and others, lstat) libc syscalls. can override -for example- lstat , chmod, can't override getdirentries (and amongst others fstatfs).
example code is:
#include <errno.h> #include <dlfcn.h> #include <stdio.h> #include <strings.h> #include <string.h> #include <sys/_timespec.h> #include <sys/stat.h> #include <sys/mount.h> #ifndef rtld_next #define rtld_next ((void *) -1l) #endif int (*getdirentries_orig)(int fd, char *buf, int nbytes, long *basep); int (*lstat_orig)(const char *path, struct stat *sb); int (*fstatfs_orig)(int fd, struct statfs *buf); int (*chmod_orig)(const char *path, mode_t mode); #define hook(func) func##_##orig = dlsym(rtld_next,#func) int getdirentries(int fd, char *buf, int nbytes, long *basep) { hook(getdirentries); printf("getdirentries\n"); return getdirentries_orig(fd, buf, nbytes, basep); } int lstat(const char *path, struct stat *sb) { hook(lstat); printf("lstat\n"); return (lstat_orig(path, sb)); } int fstatfs(int fd, struct statfs *buf) { hook(fstatfs); printf("fstatfs\n"); return fstatfs_orig(fd, buf); } int chmod(const char *path, mode_t mode) { hook(chmod); printf("chmod\n"); return chmod_orig(path, mode); } i compile on freebsd with:
cc -wall -g -o2 -fpic -shared -o preload.so preload.c (on linux, adding -ldl may needed) , use ld_preload=./preload.so bash.
if issue ls -l, "lstat" printed multiple times, that's good. ls calls multiple getdirentries too, according ktrace, , override function not called. fstatfs doesn't work.
how can override getdirentries, fstatfs , possibly other syscalls, , why aren't working in case?
thanks,
as turns out, readdir() in libc/readdir.c (readdir ls calls , should call getdirentries) calls _getdirentries, not getdirentries. if override _getdirentries, works. same fstatfs, why program did not work.
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