Cyrill Gorcunov wrote:
On Sat, Jun 16, 2012 at 01:06:46PM +0400, Cyrill Gorcunov wrote:
On Sat, Jun 16, 2012 at 12:51:04PM +0400, Konstantin Khlebnikov wrote:
"no other files mapped" requirement from my previous patch
(c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal)
is too paranoid, it forbids operation even if there mapped one shared-anon vma.
Let's check that current mm->exe_file already unmapped, in this case exe_file
symlink already outdated and its changing is reasonable.
Plus, this patch fixes exit code in case operation success.
Signed-off-by: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>
Reported-by: Cyrill Gorcunov<gorcunov@xxxxxxxxxx>
Cc: Oleg Nesterov<oleg@xxxxxxxxxx>
Cc: Matt Helsley<matthltc@xxxxxxxxxx>
Cc: Kees Cook<keescook@xxxxxxxxxxxx>
Cc: KOSAKI Motohiro<kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: Tejun Heo<tj@xxxxxxxxxx>
Cc: Pavel Emelyanov<xemul@xxxxxxxxxxxxx>
---
Ack! Thanks again, Konstantin!
Side note: there is a little nit with this patch actually,
because while when we do c/r we do "right things" and unmap
all vm-executable mappings before we set up new exe_file. But
we can't guarantee that some brave soul would not setup
new exe-file just for it's own, then what we migh have
- mm::exe_file set up and points to some file, moreover num_exe_file_vmas might be> 1
- application calls for prctl_set_mm_exe_file
- set_mm_exe_file(mm, exe_file) called, and it drops num_exe_file_vmas to 0
- finally application might call for removed_exe_file_vma
void removed_exe_file_vma(struct mm_struct *mm)
{
mm->num_exe_file_vmas--;
if ((mm->num_exe_file_vmas == 0)&& mm->exe_file) {
fput(mm->exe_file);
mm->exe_file = NULL;
}
}
and it does _not_ test for num_exe_file_vmas being 0 before doing decrement,
thus we get inconsistency in counter.
No, removed_exe_file_vma() is called only for vma with VM_EXECUTABLE flag,
there no way to get such vma other than sys_execve().
And this brave soul cannot call prctl_set_mm_exe_file() successfully,
just because for vma with VM_EXECUTABLE flag vma->vm_file == mm->exe_file.
Anyway, I plan to get rid of mm->num_exe_file_vmas and VM_EXECUTABLE.
Cyrill
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