Messages in this thread Patch in this message | | | Subject | [PATCH mm] c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal | From | Konstantin Khlebnikov <> | Date | Sat, 07 Apr 2012 23:05:54 +0400 |
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[ fix for "c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-v2" from mm tree ]
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> Cc: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Andrew Morton <akpm@linux-foundation.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> --- include/linux/sched.h | 1 + kernel/sys.c | 31 +++++++++++++++++++------------ 2 files changed, 20 insertions(+), 12 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index 81a173c..ac61e51 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -437,6 +437,7 @@ 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) diff --git a/kernel/sys.c b/kernel/sys.c index 089cb11..c6cdef5 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -1714,17 +1714,11 @@ 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; @@ -1745,17 +1739,30 @@ 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:
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