On Thu, 18 Jun 2015 19:32:18 -0700 Calvin Owens <[email protected]> wrote:
> Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
> is only exposed if CONFIG_CHECKPOINT_RESTORE is set.
>
> Each mapped file region gets a symlink in /proc/<pid>/map_files/
> corresponding to the virtual address range at which it is mapped. The
> symlinks work like the symlinks in /proc/<pid>/fd/, so you can follow
> them to the backing file even if that backing file has been unlinked.
>
> Currently, files which are mapped, unlinked, and closed are impossible
> to stat() from userspace. Exposing /proc/<pid>/map_files/ closes this
> functionality "hole".
>
> Not being able to stat() such files makes noticing and explicitly
> accounting for the space they use on the filesystem impossible. You can
> work around this by summing up the space used by every file in the
> filesystem and subtracting that total from what statfs() tells you, but
> that obviously isn't great, and it becomes unworkable once your
> filesystem becomes large enough.
>
> This patch moves map_files/ out from behind CONFIG_CHECKPOINT_RESTORE,
> and adjusts the permissions enforced on it as follows:
proc_pid_follow_link() got changed while you weren't looking, causing
fs/proc/base.c: In function 'proc_map_files_follow_link':
fs/proc/base.c:1963: warning: passing argument 2 of 'proc_pid_follow_link' from
incompatible pointer type
fs/proc/base.c:1578: note: expected 'void **' but argument is of type 'struct
nameidata *'
fs/proc/base.c:1963: warning: return discards qualifiers from pointer target
type
fs/proc/base.c: At top level:
fs/proc/base.c:1971: warning: initialization from incompatible pointer type
I just changed it to pass NULL:
---
a/fs/proc/base.c~procfs-always-expose-proc-pid-map_files-and-make-it-readable-fix
+++ a/fs/proc/base.c
@@ -1955,12 +1955,13 @@ struct map_files_info {
* symlinks may be used to bypass permissions on ancestor directories in the
* path to the file in question.
*/
-static void *proc_map_files_follow_link(struct dentry *dentry, struct
nameidata *nd)
+static void *
+proc_map_files_follow_link(struct dentry *dentry, struct nameidata *nd)
{
if (!capable(CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
- return proc_pid_follow_link(dentry, nd);
+ return proc_pid_follow_link(dentry, NULL);
}
/*
_
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
