exec: delay address limit change until point of no return

commit dac853ae89043f1b7752875300faf614de43c74b upstream.

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@googlemail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 8d128783af47374e56412d01d0488aa12af1647b..a3d0dc59067be542d7423d2a8abbc99801c0d3f6 100644 (file)
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -245,7 +245,6 @@ start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
 {
        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 --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 3c2422a99f1f8293480ad436551cfac8c600d326..9cb414381d44849274e17569be5c1f51b44eb5e1 100644 (file)
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -337,7 +337,6 @@ start_thread_common(struct pt_regs *regs, unsigned long new_ip,
        regs->cs                = _cs;
        regs->ss                = _ss;
        regs->flags             = X86_EFLAGS_IF;
-       set_fs(USER_DS);
        /*
         * Free the old FP and other extended state
         */

diff --git a/fs/exec.c b/fs/exec.c
index e03ddd4d2a97748764f6e03c45c043892a044916..34c671e4e4e32be8d38a40383407861dadc5adf7 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1024,6 +1024,7 @@ int flush_old_exec(struct linux_binprm * bprm)
 
        bprm->mm = NULL;                /* We're using it now */
 
+       set_fs(USER_DS);
        current->flags &= ~PF_RANDOMIZE;
        flush_thread();
        current->personality &= ~bprm->per_clear;
@@ -1288,10 +1289,6 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
        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;