Messages in this thread | | | Date | Fri, 9 Mar 2012 14:47:32 +0100 | From | Oleg Nesterov <> | Subject | Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3 |
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On 03/09, Cyrill Gorcunov wrote: > > On Fri, Mar 09, 2012 at 04:57:35PM +0400, Cyrill Gorcunov wrote: > > > > yeah, thanks, will update. > > > > This one should fit all requirements I hope.
Oh, sorry Cyrill, I simply can't resist...
> +static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd) > +{ > + struct file *exe_file; > + struct dentry *dentry; > + int err; > + > + if (mm->num_exe_file_vmas) > + return -EBUSY; > + > + exe_file = fget(fd); > + if (!exe_file) > + return -EBADF; > + > + dentry = exe_file->f_path.dentry; > + > + /* > + * Because the original mm->exe_file > + * points to executable file, make sure > + * this one is executable as well to not > + * break an overall picture. > + */ > + err = -EACCES; > + if (!S_ISREG(dentry->d_inode->i_mode) || > + exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC) > + goto exit; > + > + err = inode_permission(dentry->d_inode, MAY_EXEC); > + if (err) > + goto exit; > + > + /* > + * Setting new mm::exe_file is only allowed > + * when no VM_EXECUTABLE vma's left. This is > + * a special C/R case when a restored program > + * need to change own /proc/$pid/exe symlink. > + * After this call mm::num_exe_file_vmas become > + * meaningless. If mm::num_exe_file_vmas will > + * ever increase back from zero -- this code > + * needs to be revised, thus WARN_ here, just > + * to be sure.
To be shure in what??
> + */ > + down_write(&mm->mmap_sem); > + WARN_ON_ONCE(mm->num_exe_file_vmas);
We already checked it is zero. Yes, it shouldn't grow. But why do we need another check here?
If it can grow, it can grow after we drop mmap_sem as well and this would be wrong. So may be we need another WARN_ON() at the end?
I'd understand if you add something like
WARN_ON(!mm->num_exe_file_vmas && !current->in_exec);
into added_exe_file_vma().
Or
WARN_ON(mm->num_exe_file_vmas <= 0);
into removed_exe_file_vma().
But imho your WARN looks like "OK, I checked it lockless but I am not sure this is correct".
Oleg.
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