proc: do proper range check on readdir offset

Rather than pass in some random truncated offset to the pid-related
functions, check that the offset is in range up-front.

This is just cleanup, the previous commit fixed the real problem.

Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index dd6628d3ba42..dfa532730e55 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3124,11 +3124,16 @@ static int proc_pid_fill_cache(struct file *filp, void *dirent, filldir_t filldi
 /* for the /proc/ directory itself, after non-process stuff has been done */
 int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
 {
-        unsigned int nr = filp->f_pos - FIRST_PROCESS_ENTRY;
-        struct task_struct *reaper = get_proc_task(filp->f_path.dentry->d_inode);
+        unsigned int nr;
+        struct task_struct *reaper;
         struct tgid_iter iter;
         struct pid_namespace *ns;
 
+        if (filp->f_pos >= PID_MAX_LIMIT + TGID_OFFSET)
+                goto out_no_task;
+        nr = filp->f_pos - FIRST_PROCESS_ENTRY;
+
+        reaper = get_proc_task(filp->f_path.dentry->d_inode);
         if (!reaper)
                 goto out_no_task;