Revert "exec: Ensure mm->user_ns contains the execed files"submit/tizen/20190321.041604accepted/tizen/unified/20190322.075500

This reverts commit 92c624bbcc160397fcd6127cdbece1f0f20a2b97.

It was backported for fixing smack deny issue for user process
exec from kthread, but this series causes unexpected NULL pointer
deference as like following so rervert:

  Unable to handle kernel NULL pointer dereference at virtual address 000002e8
  pgd = ffffffc0127b6000
  [000002e8] *pgd=00000000527b7003, *pud=00000000527b7003, *pmd=0800000049c67003, *pte=0000000000000000
  ------------[ cut here ]------------
  Kernel BUG at ffffffc00018b4e4 [verbose debug info unavailable]
  Internal error: Oops - BUG: 96000007 [#1] PREEMPT SMP
  [...]
  PC is at would_dump+0x3c/0x9c
  LR is at would_dump+0x28/0x9c
  [...]
  Call trace:
  [<ffffffc00018b4e4>] would_dump+0x3c/0x9c
  [<ffffffc00018cd44>] do_execve_common.isra.15+0x4c8/0x568
  [<ffffffc00018d038>] compat_SyS_execve+0x28/0x3c
  Code: b940daa0 32000000 b900daa0 f9404aa0 (f9417416)
  ---[ end trace ddbe8141f552b6aa ]---

Change-Id: Ic520eb2a9936ff55e8551ef2af90b9986a3f1aba
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>

3 files changed, 4 insertions, 33 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 542f6f93c82..6caf829c0fe 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -56,7 +56,6 @@
 #include <linux/pipe_fs_i.h>
 #include <linux/oom.h>
 #include <linux/compat.h>
-#include <linux/user_namespace.h>
 #include <swap/swap_us_hooks.h>
 
 #include <asm/uaccess.h>
@@ -1093,22 +1092,8 @@ EXPORT_SYMBOL(flush_old_exec);
 
 void would_dump(struct linux_binprm *bprm, struct file *file)
 {
-	struct inode *inode = file_inode(file);
-	if (inode_permission(inode, MAY_READ) < 0) {
-		struct user_namespace *old, *user_ns;
+	if (inode_permission(file_inode(file), MAY_READ) < 0)
 		bprm->interp_flags |= BINPRM_FLAGS_ENFORCE_NONDUMP;
-
-		/* Ensure mm->user_ns contains the executable */
-		user_ns = old = bprm->mm->user_ns;
-		while ((user_ns != &init_user_ns) &&
-		       !privileged_wrt_inode_uidgid(user_ns, inode))
-			user_ns = user_ns->parent;
-
-		if (old != user_ns) {
-			bprm->mm->user_ns = get_user_ns(user_ns);
-			put_user_ns(old);
-		}
-	}
 }
 EXPORT_SYMBOL(would_dump);
 
@@ -1138,6 +1123,7 @@ void setup_new_exec(struct linux_binprm * bprm)
 	    !gid_eq(bprm->cred->gid, current_egid())) {
 		current->pdeath_signal = 0;
 	} else {
+		would_dump(bprm, bprm->file);
 		if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
 			set_dumpable(current->mm, suid_dumpable);
 	}
@@ -1551,8 +1537,6 @@ static int do_execve_common(struct filename *filename,
 	if (retval < 0)
 		goto out;
 
-	would_dump(bprm, bprm->file);
-
 	/* execve succeeded */
 	current->fs->in_exec = 0;
 	current->in_execve = 0;
diff --git a/include/linux/capability.h b/include/linux/capability.h
index 135d0a47a7c..aa93e5ef594 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -213,7 +213,6 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
 				      struct user_namespace *ns, int cap);
 extern bool capable(int cap);
 extern bool ns_capable(struct user_namespace *ns, int cap);
-extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode);
 extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
 extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
 
diff --git a/kernel/capability.c b/kernel/capability.c
index c8b748919fd..989f5bfc57d 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -428,19 +428,6 @@ bool capable(int cap)
 EXPORT_SYMBOL(capable);
 
 /**
- * privileged_wrt_inode_uidgid - Do capabilities in the namespace work over the inode?
- * @ns: The user namespace in question
- * @inode: The inode in question
- *
- * Return true if the inode uid and gid are within the namespace.
- */
-bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct inode *inode)
-{
-	return kuid_has_mapping(ns, inode->i_uid) &&
-		kgid_has_mapping(ns, inode->i_gid);
-}
-
-/**
  * capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
  * @inode: The inode in question
  * @cap: The capability in question
@@ -453,6 +440,7 @@ bool capable_wrt_inode_uidgid(const struct inode *inode, int cap)
 {
 	struct user_namespace *ns = current_user_ns();
 
-	return ns_capable(ns, cap) && privileged_wrt_inode_uidgid(ns, inode);
+	return ns_capable(ns, cap) && kuid_has_mapping(ns, inode->i_uid) &&
+		kgid_has_mapping(ns, inode->i_gid);
 }
 EXPORT_SYMBOL(capable_wrt_inode_uidgid);