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Subject[RFC v2] binfmt_misc: pass binfmt_misc flags to the interpreter
Date
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 pass the
content of the binfmt flags (special flags: P, F, C, O).

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---

Notes:
v2: only pass special flags (remove Magic and Enabled flags)

fs/binfmt_elf.c | 2 +-
fs/binfmt_elf_fdpic.c | 2 +-
fs/binfmt_misc.c | 6 ++++++
include/linux/binfmts.h | 2 +-
4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index c5642bcb6b46..7a34c03e5857 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -250,7 +250,7 @@ create_elf_tables(struct linux_binprm *bprm, 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);
+ NEW_AUX_ENT(AT_FLAGS, bprm->fmt_flags);
NEW_AUX_ENT(AT_ENTRY, exec->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));
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index d86ebd0dcc3d..8fe839be125e 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -647,7 +647,7 @@ 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);
+ NEW_AUX_ENT(AT_FLAGS, bprm->fmt_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));
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index cdb45829354d..25a392f23409 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -48,6 +48,9 @@ enum {Enabled, Magic};
#define MISC_FMT_OPEN_BINARY (1 << 30)
#define MISC_FMT_CREDENTIALS (1 << 29)
#define MISC_FMT_OPEN_FILE (1 << 28)
+#define MISC_FMT_FLAGS_MASK (MISC_FMT_PRESERVE_ARGV0 | MISC_FMT_OPEN_BINARY | \
+ MISC_FMT_CREDENTIALS | MISC_FMT_OPEN_FILE)
+

typedef struct {
struct list_head list;
@@ -149,6 +152,9 @@ static int load_misc_binary(struct linux_binprm *bprm)
if (!fmt)
return retval;

+ /* pass special flags to the interpreter */
+ bprm->fmt_flags = fmt->flags & MISC_FMT_FLAGS_MASK;
+
/* Need to be able to load the file after exec */
retval = -ENOENT;
if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index b40fc633f3be..dae0d0d7b84d 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -60,7 +60,7 @@ struct linux_binprm {
different for binfmt_{misc,script} */
unsigned interp_flags;
unsigned interp_data;
- unsigned long loader, exec;
+ unsigned long loader, exec, fmt_flags;

struct rlimit rlim_stack; /* Saved RLIMIT_STACK used during exec. */

--
2.21.0
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