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Diffstat (limited to '')
| -rw-r--r-- | src/basic/build-path.c | 274 |
1 files changed, 274 insertions, 0 deletions
diff --git a/src/basic/build-path.c b/src/basic/build-path.c new file mode 100644 index 0000000..b597265 --- /dev/null +++ b/src/basic/build-path.c @@ -0,0 +1,274 @@ +/* SPDX-License-Identifier: LGPL-2.1-or-later */ + +#include <elf.h> +#include <link.h> +#include <sys/auxv.h> + +#include "build-path.h" +#include "errno-list.h" +#include "errno-util.h" +#include "macro.h" +#include "path-util.h" +#include "process-util.h" +#include "unistd.h" + +static int get_runpath_from_dynamic(const ElfW(Dyn) *d, ElfW(Addr) bias, const char **ret) { + size_t runpath_index = SIZE_MAX, rpath_index = SIZE_MAX; + const char *strtab = NULL; + + assert(d); + + /* Iterates through the PT_DYNAMIC section to find the DT_RUNPATH/DT_RPATH entries */ + + for (; d->d_tag != DT_NULL; d++) { + + switch (d->d_tag) { + + case DT_RUNPATH: + runpath_index = (size_t) d->d_un.d_val; + break; + + case DT_RPATH: + rpath_index = (size_t) d->d_un.d_val; + break; + + case DT_STRTAB: + /* On MIPS and RISC-V DT_STRTAB records an offset, not a valid address, so it has to be adjusted + * using the bias calculated earlier. */ + if (d->d_un.d_val != 0) + strtab = (const char *) ((uintptr_t) d->d_un.d_val +#if defined(__mips__) || defined(__riscv) + + bias +#endif + ); + break; + } + + /* runpath wins, hence if we have the table and runpath we can exit the loop early */ + if (strtab && runpath_index != SIZE_MAX) + break; + } + + if (!strtab) + return -ENOTRECOVERABLE; + + /* According to ld.so runpath wins if both runpath and rpath are defined. */ + if (runpath_index != SIZE_MAX) { + if (ret) + *ret = strtab + runpath_index; + return 1; + } + + if (rpath_index != SIZE_MAX) { + if (ret) + *ret = strtab + rpath_index; + return 1; + } + + if (ret) + *ret = NULL; + + return 0; +} + +static int get_runpath(const char **ret) { + unsigned long phdr, phent, phnum; + + /* Finds the rpath/runpath in the program headers of the main executable we are running in */ + + phdr = getauxval(AT_PHDR); /* Start offset of phdr */ + if (phdr == 0) + return -ENOTRECOVERABLE; + + phnum = getauxval(AT_PHNUM); /* Number of entries in phdr */ + if (phnum == 0) + return -ENOTRECOVERABLE; + + phent = getauxval(AT_PHENT); /* Size of entries in phdr */ + if (phent < sizeof(ElfW(Phdr))) /* Safety check, that our idea of the structure matches the file */ + return -ENOTRECOVERABLE; + + ElfW(Addr) bias = 0, dyn = 0; + bool found_bias = false, found_dyn = false; + + /* Iterate through the Phdr structures to find the PT_PHDR and PT_DYNAMIC sections */ + for (unsigned long i = 0; i < phnum; i++) { + const ElfW(Phdr) *p = (const ElfW(Phdr)*) (phdr + (i * phent)); + + switch (p->p_type) { + + case PT_PHDR: + if (p->p_vaddr > phdr) /* safety overflow check */ + return -ENOTRECOVERABLE; + + bias = (ElfW(Addr)) phdr - p->p_vaddr; + found_bias = true; + break; + + case PT_DYNAMIC: + dyn = p->p_vaddr; + found_dyn = true; + break; + } + + if (found_bias && found_dyn) + break; + } + + if (!found_dyn) + return -ENOTRECOVERABLE; + + return get_runpath_from_dynamic((const ElfW(Dyn)*) (bias + dyn), bias, ret); +} + +int get_build_exec_dir(char **ret) { + int r; + + /* Returns the build execution directory if we are invoked in a build environment. Specifically, this + * checks if the main program binary has an rpath/runpath set (i.e. an explicit directory where to + * look for shared libraries) to $ORIGIN. If so we know that this is not a regular installed binary, + * but one which shall acquire its libraries from below a directory it is located in, i.e. a build + * directory or similar. In that case it typically makes sense to also search for our auxiliary + * executables we fork() off in a directory close to our main program binary, rather than in the + * system. + * + * This function is supposed to be used when looking for "callout" binaries that are closely related + * to the main program (i.e. speak a specific protocol between each other). And where it's generally + * a good idea to use the binary from the build tree (if there is one) instead of the system. + * + * Note that this does *not* actually return the rpath/runpath but the instead the directory the main + * executable was found in. This follows the logic that the result is supposed to be used for + * executable binaries (i.e. stuff in bindir), not for shared libraries (i.e. stuff in libdir), and + * hence the literal shared library path would just be wrong. + * + * TLDR: if we look for callouts in this dir first, running binaries from the meson build tree + * automatically uses the right callout. + * + * Returns: + * -ENOEXEC → We are not running in an rpath/runpath $ORIGIN environment + * -ENOENT → We don't know our own binary path + * -NOTRECOVERABLE → Dynamic binary information missing? + */ + + static int runpath_cached = -ERRNO_MAX-1; + if (runpath_cached == -ERRNO_MAX-1) { + const char *runpath = NULL; + + runpath_cached = get_runpath(&runpath); + + /* We only care if the runpath starts with $ORIGIN/ */ + if (runpath_cached > 0 && !startswith(runpath, "$ORIGIN/")) + runpath_cached = 0; + } + if (runpath_cached < 0) + return runpath_cached; + if (runpath_cached == 0) + return -ENOEXEC; + + _cleanup_free_ char *exe = NULL; + r = get_process_exe(0, &exe); + if (r < 0) + return runpath_cached = r; + + return path_extract_directory(exe, ret); +} + +static int find_build_dir_binary(const char *fn, char **ret) { + int r; + + assert(fn); + assert(ret); + + _cleanup_free_ char *build_dir = NULL; + r = get_build_exec_dir(&build_dir); + if (r < 0) + return r; + + _cleanup_free_ char *np = path_join(build_dir, fn); + if (!np) + return -ENOMEM; + + *ret = TAKE_PTR(np); + return 0; +} + +static int find_environment_binary(const char *fn, const char **ret) { + + /* If a path such as /usr/lib/systemd/systemd-foobar is specified, then this will check for an + * environment variable SYSTEMD_FOOBAR_PATH and return it if set. */ + + _cleanup_free_ char *s = strdup(fn); + if (!s) + return -ENOMEM; + + ascii_strupper(s); + string_replace_char(s, '-', '_'); + + if (!strextend(&s, "_PATH")) + return -ENOMEM; + + const char *e; + e = secure_getenv(s); + if (!e) + return -ENXIO; + + *ret = e; + return 0; +} + +int invoke_callout_binary(const char *path, char *const argv[]) { + int r; + + assert(path); + + /* Just like execv(), but tries to execute the specified binary in the build dir instead, if known */ + + _cleanup_free_ char *fn = NULL; + r = path_extract_filename(path, &fn); + if (r < 0) + return r; + if (r == O_DIRECTORY) /* Uh? */ + return -EISDIR; + + const char *e; + if (find_environment_binary(fn, &e) >= 0) { + /* If there's an explicit environment variable set for this binary, prefer it */ + execv(e, argv); + return -errno; /* The environment variable counts, let's fail otherwise */ + } + + _cleanup_free_ char *np = NULL; + if (find_build_dir_binary(fn, &np) >= 0) + execv(np, argv); + + execv(path, argv); + return -errno; +} + +int pin_callout_binary(const char *path) { + int r; + + assert(path); + + /* Similar to invoke_callout_binary(), but pins (i.e. O_PATH opens) the binary instead of executing it. */ + + _cleanup_free_ char *fn = NULL; + r = path_extract_filename(path, &fn); + if (r < 0) + return r; + if (r == O_DIRECTORY) /* Uh? */ + return -EISDIR; + + const char *e; + if (find_environment_binary(fn, &e) >= 0) + return RET_NERRNO(open(e, O_CLOEXEC|O_PATH)); + + _cleanup_free_ char *np = NULL; + if (find_build_dir_binary(fn, &np) >= 0) { + r = RET_NERRNO(open(np, O_CLOEXEC|O_PATH)); + if (r >= 0) + return r; + } + + return RET_NERRNO(open(path, O_CLOEXEC|O_PATH)); +} |