[PATCH] proc: #68991 Fix GPF in /proc/$PID/map_files

[Eric W. Biederman]

Artem Fetishev <artem_fetishev at epam.com> writes:

> https://bugzilla.kernel.org/show_bug.cgi?id=68991
>
> The expected logic of proc_map_files_get_link() is either to return 0 and
> initialize 'path' or return an error and leave 'path' uninitialized. By the time
> dname_to_vma_addr() returns 0 the corresponding vma may have already be gone. In
> this case the path is not initialized but the return value is still 0. This
> results in 'general protection fault' inside d_path().
>
> Steps to reproduce:
> CONFIG_CHECKPOINT_RESTORE=y
>
> fd = open(...);
> while (1) {
> 	mmap(fd, ...);
> 	munmap(fd, ...);
> }
>
> ls -la /proc/$PID/map_files
>
> Signed-off-by: Artem Fetishev <artem_fetishev at epam.com>
> Signed-off-by: Aleksandr Terekhov <aleksandr_terekhov at epam.com>
Reviewed-by: "Eric W. Biederman" <ebiederm at xmission.com>
> ---
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 5150706..b976062 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1824,6 +1824,7 @@ static int proc_map_files_get_link(struct dentry *dentry, struct path *path)
>  	if (rc)
>  		goto out_mmput;
>  
> +	rc = -ENOENT;
>  	down_read(&mm->mmap_sem);
>  	vma = find_exact_vma(mm, vm_start, vm_end);
>  	if (vma && vma->vm_file) {
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