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c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal

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A fix for commit b32dfe3771 ("c/r: prctl: add ability to set new
mm_struct::exe_file").

After removing mm->num_exe_file_vmas kernel keeps mm->exe_file until
final mmput(), it never becomes NULL while task is alive.

We can check for other mapped files in mm instead of checking
mm->num_exe_file_vmas, and mark mm with flag MMF_EXE_FILE_CHANGED in
order to forbid second changing of mm->exe_file.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov 2012-06-07 14:21:11 -07:00 committed by Linus Torvalds
parent 6305902c2f
commit bafb282df2
2 changed files with 20 additions and 12 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

1
include/linux/sched.h
View file

@ -439,6 +439,7 @@ extern int get_dumpable(struct mm_struct *mm);
/* leave room for more dump flags */
#define MMF_VM_MERGEABLE 16 /* KSM may merge identical pages */
#define MMF_VM_HUGEPAGE 17 /* set when VM_HUGEPAGE is set on vma */
#define MMF_EXE_FILE_CHANGED 18 /* see prctl_set_mm_exe_file() */
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)

31
kernel/sys.c
View file

@ -1796,17 +1796,11 @@ static bool vma_flags_mismatch(struct vm_area_struct *vma,
static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
{
struct vm_area_struct *vma;
struct file *exe_file;
struct dentry *dentry;
int err;
/*
* Setting new mm::exe_file is only allowed when no VM_EXECUTABLE vma's
* remain. So perform a quick test first.
*/
if (mm->num_exe_file_vmas)
return -EBUSY;
exe_file = fget(fd);
if (!exe_file)
return -EBADF;
@ -1827,17 +1821,30 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
if (err)
goto exit;
down_write(&mm->mmap_sem);
/*
* Forbid mm->exe_file change if there are mapped other files.
*/
err = -EBUSY;
for (vma = mm->mmap; vma; vma = vma->vm_next) {
if (vma->vm_file && !path_equal(&vma->vm_file->f_path,
&exe_file->f_path))
goto exit_unlock;
}
/*
* The symlink can be changed only once, just to disallow arbitrary
* transitions malicious software might bring in. This means one
* could make a snapshot over all processes running and monitor
* /proc/pid/exe changes to notice unusual activity if needed.
*/
down_write(&mm->mmap_sem);
if (likely(!mm->exe_file))
set_mm_exe_file(mm, exe_file);
else
err = -EBUSY;
err = -EPERM;
if (test_and_set_bit(MMF_EXE_FILE_CHANGED, &mm->flags))
goto exit_unlock;
set_mm_exe_file(mm, exe_file);
exit_unlock:
up_write(&mm->mmap_sem);
exit: