[PATCH 1/2] procfs: Allow reading fdinfo with PTRACE_MODE_READ

[Kalesh Singh]

Since fdinfo doesn't permit reading process memory and manipulating
process state, allow accessing fdinfo under PTRACE_MODE_READ_FSCRED.

Suggested-by: Jann Horn <ja...@google.com>
Signed-off-by: Kalesh Singh <kaleshsi...@google.com>
---
 fs/proc/base.c |  4 ++--
 fs/proc/fd.c   | 15 ++++++++++++++-
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index b3422cda2a91..a37f9de7103f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3160,7 +3160,7 @@ 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),
        DIR("map_files",  S_IRUSR|S_IXUSR, proc_map_files_inode_operations, 
proc_map_files_operations),
-       DIR("fdinfo",     S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, 
proc_fdinfo_operations),
+       DIR("fdinfo",     S_IRUGO|S_IXUGO, 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
        DIR("net",        S_IRUGO|S_IXUGO, proc_net_inode_operations, 
proc_net_operations),
@@ -3504,7 +3504,7 @@ static const struct inode_operations 
proc_tid_comm_inode_operations = {
  */
 static const struct pid_entry tid_base_stuff[] = {
        DIR("fd",        S_IRUSR|S_IXUSR, proc_fd_inode_operations, 
proc_fd_operations),
-       DIR("fdinfo",    S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, 
proc_fdinfo_operations),
+       DIR("fdinfo",    S_IRUGO|S_IXUGO, 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
        DIR("net",        S_IRUGO|S_IXUGO, proc_net_inode_operations, 
proc_net_operations),
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index cb51763ed554..585e213301f9 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -6,6 +6,7 @@
 #include <linux/fdtable.h>
 #include <linux/namei.h>
 #include <linux/pid.h>
+#include <linux/ptrace.h>
 #include <linux/security.h>
 #include <linux/file.h>
 #include <linux/seq_file.h>
@@ -72,6 +73,18 @@ static int seq_show(struct seq_file *m, void *v)
 
 static int seq_fdinfo_open(struct inode *inode, struct file *file)
 {
+       bool allowed = false;
+       struct task_struct *task = get_proc_task(inode);
+
+       if (!task)
+               return -ESRCH;
+
+       allowed = ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS);
+       put_task_struct(task);
+
+       if (!allowed)
+               return -EACCES;
+
        return single_open(file, seq_show, inode);
 }
 
@@ -307,7 +320,7 @@ static struct dentry *proc_fdinfo_instantiate(struct dentry 
*dentry,
        struct proc_inode *ei;
        struct inode *inode;
 
-       inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUSR);
+       inode = proc_pid_make_inode(dentry->d_sb, task, S_IFREG | S_IRUGO);
        if (!inode)
                return ERR_PTR(-ENOENT);
 
-- 
2.30.0.365.g02bc693789-goog