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    SubjectRe: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3
    On 03/09, Cyrill Gorcunov wrote:
    >
    > +static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
    > +{
    > + struct file *exe_file;
    > + struct dentry *dentry;
    > + int err;
    > +
    > + 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 executable VMAs left. This is
    ^^^^^^^^^^
    Perhaps this is just me, but imho "executable" is not clear enough.
    I'd suggest VM_EXECUTABLE to avoid the confusion with VM_EXEC.

    > + * 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.
    > + */
    > + down_write(&mm->mmap_sem);
    > + if (mm->num_exe_file_vmas == 0) {

    You can check this at the very start lockless and simplify the code.
    Once it is zero, it can never grow (or we have a bug anyway).

    > + set_mm_exe_file(mm, exe_file);
    > + exe_file = NULL;
    > + } else
    > + err = -EBUSY;
    > + up_write(&mm->mmap_sem);
    > +
    > +exit:
    > + if (exe_file)
    > + fput(exe_file);

    This doesn't look correct, you need fput() in any case.
    set_mm_exe_file() does another get_file().

    Oleg.



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