linux-kernel - [PATCH 1/3] binfmt: Move install_exec_creds after setup_new_exec to match binfmt

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Date:   Mon, 06 Apr 2020 20:31:25 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Bernd Edlinger <bernd.edlinger@...mail.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexey Gladkov <gladkov.alexey@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH 1/3] binfmt: Move install_exec_creds after setup_new_exec to match binfmt_elf


In 2016 Linus moved install_exec_creds immediately after
setup_new_exec, in binfmt_elf as a cleanup and as part of closing a
potential information leak.

Perform the same cleanup for the other binary formats.

Different binary formats doing the same things the same way makes exec
easier to reason about and easier to maintain.

Putting install_exec_creds immediate after setup_new_exec makes many
simplifications possible in the code.

Ref: 9f834ec18def ("binfmt_elf: switch to new creds when switching to new mm")
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 arch/x86/ia32/ia32_aout.c | 3 +--
 fs/binfmt_aout.c          | 2 +-
 fs/binfmt_elf_fdpic.c     | 2 +-
 fs/binfmt_flat.c          | 3 +--
 4 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index 9bb71abd66bd..37b36a8ce5fa 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -140,6 +140,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
 	set_personality_ia32(false);
 
 	setup_new_exec(bprm);
+	install_exec_creds(bprm);
 
 	regs->cs = __USER32_CS;
 	regs->r8 = regs->r9 = regs->r10 = regs->r11 = regs->r12 =
@@ -156,8 +157,6 @@ static int load_aout_binary(struct linux_binprm *bprm)
 	if (retval < 0)
 		return retval;
 
-	install_exec_creds(bprm);
-
 	if (N_MAGIC(ex) == OMAGIC) {
 		unsigned long text_addr, map_size;
 
diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index 8e8346a81723..ace587b66904 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -162,6 +162,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
 	set_personality(PER_LINUX);
 #endif
 	setup_new_exec(bprm);
+	install_exec_creds(bprm);
 
 	current->mm->end_code = ex.a_text +
 		(current->mm->start_code = N_TXTADDR(ex));
@@ -174,7 +175,6 @@ static int load_aout_binary(struct linux_binprm * bprm)
 	if (retval < 0)
 		return retval;
 
-	install_exec_creds(bprm);
 
 	if (N_MAGIC(ex) == OMAGIC) {
 		unsigned long text_addr, map_size;
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index 240f66663543..6c94c6d53d97 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -353,6 +353,7 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
 		current->personality |= READ_IMPLIES_EXEC;
 
 	setup_new_exec(bprm);
+	install_exec_creds(bprm);
 
 	set_binfmt(&elf_fdpic_format);
 
@@ -434,7 +435,6 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
 	current->mm->start_stack = current->mm->start_brk + stack_size;
 #endif
 
-	install_exec_creds(bprm);
 	if (create_elf_fdpic_tables(bprm, current->mm,
 				    &exec_params, &interp_params) < 0)
 		goto error;
diff --git a/fs/binfmt_flat.c b/fs/binfmt_flat.c
index 831a2b25ba79..1a1d1fcb893f 100644
--- a/fs/binfmt_flat.c
+++ b/fs/binfmt_flat.c
@@ -541,6 +541,7 @@ static int load_flat_file(struct linux_binprm *bprm,
 		/* OK, This is the point of no return */
 		set_personality(PER_LINUX_32BIT);
 		setup_new_exec(bprm);
+		install_exec_creds(bprm);
 	}
 
 	/*
@@ -963,8 +964,6 @@ static int load_flat_binary(struct linux_binprm *bprm)
 		}
 	}
 
-	install_exec_creds(bprm);
-
 	set_binfmt(&flat_format);
 
 #ifdef CONFIG_MMU
-- 
2.25.0