The patch titled
exec: delay address limit change until point of no return
has been added to the -mm tree. Its filename is
exec-delay-address-limit-change-until-point-of-no-return.patch
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------------------------------------------------------
Subject: exec: delay address limit change until point of no return
From: Mathias Krause <minipli@xxxxxxxxxxxxxx>
We use kernel_execve() to transfer control of the init procces from
kernel to userland. If the program to start as init process isn't given
on the kernel command line or fails to start we use a few hardcoded
fallbacks. This fallback mechanism does not work when we encounter a
file that is executable but fails to start, e.g. due to a missing
library dependency or by having an unsupported file format.
Unconditionally changing the address limit to USER_DS and not restoring it
to its old value in the error path is wrong because it prevents us using
kernel memory on repeated calls to this function. This, in fact, breaks
the fallback of hard coded paths to the init program from being ever
successful if the first candidate fails to load.
With this patch applied switching to USER_DS is delayed until the point of
no return is reached which makes it possible to have a multi-arch rootfs
with one arch specific init binary for each of the (hard coded) probed
paths.
Since the address limit is already set to USER_DS when start_thread()
will be invoked, this redundancy can be safely removed.
Signed-off-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/process_32.c | 1 -
arch/x86/kernel/process_64.c | 1 -
fs/exec.c | 5 +----
3 files changed, 1 insertion(+), 6 deletions(-)
diff -puN arch/x86/kernel/process_32.c~exec-delay-address-limit-change-until-point-of-no-return arch/x86/kernel/process_32.c
--- a/arch/x86/kernel/process_32.c~exec-delay-address-limit-change-until-point-of-no-return
+++ a/arch/x86/kernel/process_32.c
@@ -245,7 +245,6 @@ start_thread(struct pt_regs *regs, unsig
{
set_user_gs(regs, 0);
regs->fs = 0;
- set_fs(USER_DS);
regs->ds = __USER_DS;
regs->es = __USER_DS;
regs->ss = __USER_DS;
diff -puN arch/x86/kernel/process_64.c~exec-delay-address-limit-change-until-point-of-no-return arch/x86/kernel/process_64.c
--- a/arch/x86/kernel/process_64.c~exec-delay-address-limit-change-until-point-of-no-return
+++ a/arch/x86/kernel/process_64.c
@@ -338,7 +338,6 @@ start_thread_common(struct pt_regs *regs
regs->cs = _cs;
regs->ss = _ss;
regs->flags = X86_EFLAGS_IF;
- set_fs(USER_DS);
/*
* Free the old FP and other extended state
*/
diff -puN fs/exec.c~exec-delay-address-limit-change-until-point-of-no-return fs/exec.c
--- a/fs/exec.c~exec-delay-address-limit-change-until-point-of-no-return
+++ a/fs/exec.c
@@ -1093,6 +1093,7 @@ int flush_old_exec(struct linux_binprm *
bprm->mm = NULL; /* We're using it now */
+ set_fs(USER_DS);
current->flags &= ~(PF_RANDOMIZE | PF_KTHREAD);
flush_thread();
current->personality &= ~bprm->per_clear;
@@ -1357,10 +1358,6 @@ int search_binary_handler(struct linux_b
if (retval)
return retval;
- /* kernel module loader fixup */
- /* so we don't try to load run modprobe in kernel space. */
- set_fs(USER_DS);
-
retval = audit_bprm(bprm);
if (retval)
return retval;
_
Patches currently in -mm which might be from minipli@xxxxxxxxxxxxxx are
exec-delay-address-limit-change-until-point-of-no-return.patch
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