Messages in this thread Patch in this message | | | Date | Wed, 15 Jul 2015 15:21:49 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH v7] procfs: Always expose /proc/<pid>/map_files/ and make it readable |
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On Thu, 18 Jun 2015 19:32:18 -0700 Calvin Owens <calvinowens@fb.com> 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); } /* _
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