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binfmt_misc: pass binfmt_misc flags to the interpreter 

It can be useful to the interpreter to know which flags are in use.

For instance, knowing if the preserve-argv[0] is in use would
allow to skip the pathname argument.

This patch uses an unused auxiliary vector, AT_FLAGS, to add a
flag to inform interpreter if the preserve-argv[0] is enabled.

Note by Helge Deller:
The real-world user of this patch is qemu-user, which needs to know
if it has to preserve the argv[0]. See Debian bug #970460.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: YunQiang Su <ysu@wavecomp.com>
URL: http://bugs.debian.org/970460
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Laurent Vivier 2020-01-28 14:25:39 +01:00 committed by Helge Deller
parent b7795074a0
commit 2347961b11
5 changed files with 19 additions and 3 deletions
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5
fs/binfmt_elf.c
View File

@ -186,6 +186,7 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
unsigned char k_rand_bytes[16];
int items;
elf_addr_t *elf_info;
elf_addr_t flags = 0;
int ei_index;
const struct cred *cred = current_cred();
struct vm_area_struct *vma;
@ -260,7 +261,9 @@ create_elf_tables(struct linux_binprm *bprm, const struct elfhdr *exec,
NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
NEW_AUX_ENT(AT_PHNUM, exec->e_phnum);
NEW_AUX_ENT(AT_BASE, interp_load_addr);
NEW_AUX_ENT(AT_FLAGS, 0);
if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
flags |= AT_FLAGS_PRESERVE_ARGV0;
NEW_AUX_ENT(AT_FLAGS, flags);
NEW_AUX_ENT(AT_ENTRY, e_entry);
NEW_AUX_ENT(AT_UID, from_kuid_munged(cred->user_ns, cred->uid));
NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));

5
fs/binfmt_elf_fdpic.c
View File

@ -506,6 +506,7 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
char __user *u_platform, *u_base_platform, *p;
int loop;
int nr; /* reset for each csp adjustment */
unsigned long flags = 0;
#ifdef CONFIG_MMU
/* In some cases (e.g. Hyper-Threading), we want to avoid L1 evictions
@ -648,7 +649,9 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
NEW_AUX_ENT(AT_PHENT, sizeof(struct elf_phdr));
NEW_AUX_ENT(AT_PHNUM, exec_params->hdr.e_phnum);
NEW_AUX_ENT(AT_BASE, interp_params->elfhdr_addr);
NEW_AUX_ENT(AT_FLAGS, 0);
if (bprm->interp_flags & BINPRM_FLAGS_PRESERVE_ARGV0)
flags |= AT_FLAGS_PRESERVE_ARGV0;
NEW_AUX_ENT(AT_FLAGS, flags);
NEW_AUX_ENT(AT_ENTRY, exec_params->entry_addr);
NEW_AUX_ENT(AT_UID, (elf_addr_t) from_kuid_munged(cred->user_ns, cred->uid));
NEW_AUX_ENT(AT_EUID, (elf_addr_t) from_kuid_munged(cred->user_ns, cred->euid));

4
fs/binfmt_misc.c
View File

@ -153,7 +153,9 @@ static int load_misc_binary(struct linux_binprm *bprm)
if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
goto ret;
if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
} else {
retval = remove_arg_zero(bprm);
if (retval)
goto ret;

4
include/linux/binfmts.h
View File

@ -73,6 +73,10 @@ struct linux_binprm {
#define BINPRM_FLAGS_PATH_INACCESSIBLE_BIT 2
#define BINPRM_FLAGS_PATH_INACCESSIBLE (1 << BINPRM_FLAGS_PATH_INACCESSIBLE_BIT)
/* preserve argv0 for the interpreter */
#define BINPRM_FLAGS_PRESERVE_ARGV0_BIT 3
#define BINPRM_FLAGS_PRESERVE_ARGV0 (1 << BINPRM_FLAGS_PRESERVE_ARGV0_BIT)
/* Function parameter for binfmt->coredump */
struct coredump_params {
const kernel_siginfo_t *siginfo;

4
include/uapi/linux/binfmts.h
View File

@ -18,4 +18,8 @@ struct pt_regs;
/* sizeof(linux_binprm->buf) */
#define BINPRM_BUF_SIZE 256
/* preserve argv0 for the interpreter */
#define AT_FLAGS_PRESERVE_ARGV0_BIT 0
#define AT_FLAGS_PRESERVE_ARGV0 (1 << AT_FLAGS_PRESERVE_ARGV0_BIT)
#endif /* _UAPI_LINUX_BINFMTS_H */