Files
linux_media/include/linux/binfmts.h
Eric W. Biederman 56305aa9b6 exec: Compute file based creds only once
Move the computation of creds from prepare_binfmt into begin_new_exec
so that the creds need only be computed once.  This is just code
reorganization no semantic changes of any kind are made.

Moving the computation is safe.  I have looked through the kernel and
verified none of the binfmts look at bprm->cred directly, and that
there are no helpers that look at bprm->cred indirectly.  Which means
that it is not a problem to compute the bprm->cred later in the
execution flow as it is not used until it becomes current->cred.

A new function bprm_creds_from_file is added to contain the work that
needs to be done.  bprm_creds_from_file first computes which file
bprm->executable or most likely bprm->file that the bprm->creds
will be computed from.

The funciton bprm_fill_uid is updated to receive the file instead of
accessing bprm->file.  The now unnecessary work needed to reset the
bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid.
A small comment to document that bprm_fill_uid now only deals with the
work to handle suid and sgid files.  The default case is already
heandled by prepare_exec_creds.

The function security_bprm_repopulate_creds is renamed
security_bprm_creds_from_file and now is explicitly passed the file
from which to compute the creds.  The documentation of the
bprm_creds_from_file security hook is updated to explain when the hook
is called and what it needs to do.  The file is passed from
cap_bprm_creds_from_file into get_file_caps so that the caps are
computed for the appropriate file.  The now unnecessary work in
cap_bprm_creds_from_file to reset the ambient capabilites has been
removed.  A small comment to document that the work of
cap_bprm_creds_from_file is to read capabilities from the files
secureity attribute and derive capabilities from the fact the
user had uid 0 has been added.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2020-05-29 22:00:54 -05:00

148 lines
4.5 KiB
C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_BINFMTS_H
#define _LINUX_BINFMTS_H
#include <linux/sched.h>
#include <linux/unistd.h>
#include <asm/exec.h>
#include <uapi/linux/binfmts.h>
struct filename;
#define CORENAME_MAX_SIZE 128
/*
* This structure is used to hold the arguments that are used when loading binaries.
*/
struct linux_binprm {
#ifdef CONFIG_MMU
struct vm_area_struct *vma;
unsigned long vma_pages;
#else
# define MAX_ARG_PAGES 32
struct page *page[MAX_ARG_PAGES];
#endif
struct mm_struct *mm;
unsigned long p; /* current top of mem */
unsigned long argmin; /* rlimit marker for copy_strings() */
unsigned int
/* Should an execfd be passed to userspace? */
have_execfd:1,
/* Use the creds of a script (see binfmt_misc) */
execfd_creds:1,
/*
* Set by bprm_creds_for_exec hook to indicate a
* privilege-gaining exec has happened. Used to set
* AT_SECURE auxv for glibc.
*/
secureexec:1,
/*
* Set when errors can no longer be returned to the
* original userspace.
*/
point_of_no_return:1;
#ifdef __alpha__
unsigned int taso:1;
#endif
struct file * executable; /* Executable to pass to the interpreter */
struct file * interpreter;
struct file * file;
struct cred *cred; /* new credentials */
int unsafe; /* how unsafe this exec is (mask of LSM_UNSAFE_*) */
unsigned int per_clear; /* bits to clear in current->personality */
int argc, envc;
const char * filename; /* Name of binary as seen by procps */
const char * interp; /* Name of the binary really executed. Most
of the time same as filename, but could be
different for binfmt_{misc,script} */
unsigned interp_flags;
int execfd; /* File descriptor of the executable */
unsigned long loader, exec;
struct rlimit rlim_stack; /* Saved RLIMIT_STACK used during exec. */
char buf[BINPRM_BUF_SIZE];
} __randomize_layout;
#define BINPRM_FLAGS_ENFORCE_NONDUMP_BIT 0
#define BINPRM_FLAGS_ENFORCE_NONDUMP (1 << BINPRM_FLAGS_ENFORCE_NONDUMP_BIT)
/* filename of the binary will be inaccessible after exec */
#define BINPRM_FLAGS_PATH_INACCESSIBLE_BIT 2
#define BINPRM_FLAGS_PATH_INACCESSIBLE (1 << BINPRM_FLAGS_PATH_INACCESSIBLE_BIT)
/* Function parameter for binfmt->coredump */
struct coredump_params {
const kernel_siginfo_t *siginfo;
struct pt_regs *regs;
struct file *file;
unsigned long limit;
unsigned long mm_flags;
loff_t written;
loff_t pos;
};
/*
* This structure defines the functions that are used to load the binary formats that
* linux accepts.
*/
struct linux_binfmt {
struct list_head lh;
struct module *module;
int (*load_binary)(struct linux_binprm *);
int (*load_shlib)(struct file *);
int (*core_dump)(struct coredump_params *cprm);
unsigned long min_coredump; /* minimal dump size */
} __randomize_layout;
extern void __register_binfmt(struct linux_binfmt *fmt, int insert);
/* Registration of default binfmt handlers */
static inline void register_binfmt(struct linux_binfmt *fmt)
{
__register_binfmt(fmt, 0);
}
/* Same as above, but adds a new binfmt at the top of the list */
static inline void insert_binfmt(struct linux_binfmt *fmt)
{
__register_binfmt(fmt, 1);
}
extern void unregister_binfmt(struct linux_binfmt *);
extern int __must_check remove_arg_zero(struct linux_binprm *);
extern int begin_new_exec(struct linux_binprm * bprm);
extern void setup_new_exec(struct linux_binprm * bprm);
extern void finalize_exec(struct linux_binprm *bprm);
extern void would_dump(struct linux_binprm *, struct file *);
extern int suid_dumpable;
/* Stack area protections */
#define EXSTACK_DEFAULT 0 /* Whatever the arch defaults to */
#define EXSTACK_DISABLE_X 1 /* Disable executable stacks */
#define EXSTACK_ENABLE_X 2 /* Enable executable stacks */
extern int setup_arg_pages(struct linux_binprm * bprm,
unsigned long stack_top,
int executable_stack);
extern int transfer_args_to_stack(struct linux_binprm *bprm,
unsigned long *sp_location);
extern int bprm_change_interp(const char *interp, struct linux_binprm *bprm);
extern int copy_strings_kernel(int argc, const char *const *argv,
struct linux_binprm *bprm);
extern void set_binfmt(struct linux_binfmt *new);
extern ssize_t read_code(struct file *, unsigned long, loff_t, size_t);
extern int do_execve(struct filename *,
const char __user * const __user *,
const char __user * const __user *);
extern int do_execveat(int, struct filename *,
const char __user * const __user *,
const char __user * const __user *,
int);
int do_execve_file(struct file *file, void *__argv, void *__envp);
#endif /* _LINUX_BINFMTS_H */