Commit bafb282d authored by Konstantin Khlebnikov's avatar Konstantin Khlebnikov Committed by Linus Torvalds
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c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal 



A fix for commit b32dfe37 ("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: default avatarKonstantin Khlebnikov <khlebnikov@openvz.org>
Reviewed-by: default avatarCyrill 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6305902c

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

kernel/sys.c

+19 −12
Original line number Diff line number Diff line
@@ -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))

	err = -EPERM;

	if (test_and_set_bit(MMF_EXE_FILE_CHANGED, &mm->flags))

		goto exit_unlock;



	set_mm_exe_file(mm, exe_file);

	else

		err = -EBUSY;

exit_unlock:

	up_write(&mm->mmap_sem);



exit:

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