linux-kernel - [RFC v2] binfmt_misc: pass binfmt

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Message-Id: <20191122150830.15855-1-laurent@vivier.eu>
Date:   Fri, 22 Nov 2019 16:08:30 +0100
From:   Laurent Vivier <laurent@...ier.eu>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Laurent Vivier <laurent@...ier.eu>
Subject: [RFC v2] 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 pass the
content of the binfmt flags (special flags: P, F, C, O).

Signed-off-by: Laurent Vivier <laurent@...ier.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