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Subject[RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and make it readable
Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
is very useful for enumerating the files mapped into a process when
the more verbose information in /proc/<pid>/maps is not needed.

This patch moves the folder out from behind CHECKPOINT_RESTORE, and
removes the CAP_SYS_ADMIN restrictions. Following the links requires
the ability to ptrace the process in question, so this doesn't allow
an attacker to do anything they couldn't already do before.

Signed-off-by: Calvin Owens <calvinowens@fb.com>
---
Changes in v2: Removed the follow_link() stub that returned -EPERM if
the caller didn't have CAP_SYS_ADMIN, since the caller
in my chroot() scenario gets -EACCES anyway.

fs/proc/base.c | 18 ------------------
1 file changed, 18 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 3f3d7ae..67b15ac 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1632,8 +1632,6 @@ end_instantiate:
return dir_emit(ctx, name, len, 1, DT_UNKNOWN);
}

-#ifdef CONFIG_CHECKPOINT_RESTORE
-
/*
* dname_to_vma_addr - maps a dentry name into two unsigned longs
* which represent vma start and end addresses.
@@ -1660,11 +1658,6 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
if (flags & LOOKUP_RCU)
return -ECHILD;

- if (!capable(CAP_SYS_ADMIN)) {
- status = -EPERM;
- goto out_notask;
- }
-
inode = dentry->d_inode;
task = get_proc_task(inode);
if (!task)
@@ -1792,10 +1785,6 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
int result;
struct mm_struct *mm;

- result = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
- goto out;
-
result = -ENOENT;
task = get_proc_task(dir);
if (!task)
@@ -1849,10 +1838,6 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
struct map_files_info *p;
int ret;

- ret = -EPERM;
- if (!capable(CAP_SYS_ADMIN))
- goto out;
-
ret = -ENOENT;
task = get_proc_task(file_inode(file));
if (!task)
@@ -2040,7 +2025,6 @@ static const struct file_operations proc_timers_operations = {
.llseek = seq_lseek,
.release = seq_release_private,
};
-#endif /* CONFIG_CHECKPOINT_RESTORE */

static int proc_pident_instantiate(struct inode *dir,
struct dentry *dentry, struct task_struct *task, const void *ptr)
@@ -2537,9 +2521,7 @@ static const struct inode_operations proc_task_inode_operations;
static const struct pid_entry tgid_base_stuff[] = {
DIR("task", S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
DIR("fd", S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
-#ifdef CONFIG_CHECKPOINT_RESTORE
DIR("map_files", S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
-#endif
DIR("fdinfo", S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
DIR("ns", S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
#ifdef CONFIG_NET
--
1.8.1


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