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From: David Hildenbrand <david@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: "David Hildenbrand" <david@redhat.com>,
	"Linus Torvalds" <torvalds@linux-foundation.org>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Alexey Dobriyan" <adobriyan@gmail.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Arnaldo Carvalho de Melo" <acme@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Alexander Shishkin" <alexander.shishkin@linux.intel.com>,
	"Jiri Olsa" <jolsa@redhat.com>,
	"Namhyung Kim" <namhyung@kernel.org>,
	"Petr Mladek" <pmladek@suse.com>,
	"Sergey Senozhatsky" <sergey.senozhatsky@gmail.com>,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Rasmus Villemoes" <linux@rasmusvillemoes.dk>,
	"Kees Cook" <keescook@chromium.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"Greg Ungerer" <gerg@linux-m68k.org>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Vincenzo Frascino" <vincenzo.frascino@arm.com>,
	"Chinwen Chang" <chinwen.chang@mediatek.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	"Huang Ying" <ying.huang@intel.com>,
	"Jann Horn" <jannh@google.com>, "Feng Tang" <feng.tang@intel.com>,
	"Kevin Brodsky" <Kevin.Brodsky@arm.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Shawn Anastasio" <shawn@anastas.io>,
	"Steven Price" <steven.price@arm.com>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Christian Brauner" <christian.brauner@ubuntu.com>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Gabriel Krisman Bertazi" <krisman@collabora.com>,
	"Peter Xu" <peterx@redhat.com>,
	"Suren Baghdasaryan" <surenb@google.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	"Marco Elver" <elver@google.com>,
	"Daniel Jordan" <daniel.m.jordan@oracle.com>,
	"Nicolas Viennot" <Nicolas.Viennot@twosigma.com>,
	"Thomas Cedeno" <thomascedeno@google.com>,
	"Michal Hocko" <mhocko@suse.com>,
	"Miklos Szeredi" <miklos@szeredi.hu>,
	"Chengguang Xu" <cgxu519@mykernel.net>,
	"Christian König" <ckoenig.leichtzumerken@gmail.com>,
	"Florian Weimer" <fweimer@redhat.com>,
	"David Laight" <David.Laight@ACULAB.COM>,
	linux-unionfs@vger.kernel.org, linux-api@vger.kernel.org,
	x86@kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: [PATCH v2 2/7] kernel/fork: factor out replacing the current MM exe_file
Date: Mon, 16 Aug 2021 21:48:35 +0200	[thread overview]
Message-ID: <20210816194840.42769-3-david@redhat.com> (raw)
In-Reply-To: <20210816194840.42769-1-david@redhat.com>

Let's factor the main logic out into replace_mm_exe_file(), such that
all mm->exe_file logic is contained in kernel/fork.c.

While at it, perform some simple cleanups that are possible now that
we're simplifying the individual functions.

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 include/linux/mm.h |  1 +
 kernel/fork.c      | 44 +++++++++++++++++++++++++++++++++++++++++---
 kernel/sys.c       | 33 +--------------------------------
 3 files changed, 43 insertions(+), 35 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7ca22e6e694a..48c6fa9ab792 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2581,6 +2581,7 @@ extern int mm_take_all_locks(struct mm_struct *mm);
 extern void mm_drop_all_locks(struct mm_struct *mm);
 
 extern void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
+extern int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file);
 extern struct file *get_mm_exe_file(struct mm_struct *mm);
 extern struct file *get_task_exe_file(struct task_struct *task);
 
diff --git a/kernel/fork.c b/kernel/fork.c
index bc94b2cc5995..eedce5c77041 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1148,9 +1148,7 @@ void mmput_async(struct mm_struct *mm)
  *
  * Main users are mmput() and sys_execve(). Callers prevent concurrent
  * invocations: in mmput() nobody alive left, in execve task is single
- * threaded. sys_prctl(PR_SET_MM_MAP/EXE_FILE) also needs to set the
- * mm->exe_file, but does so without using set_mm_exe_file() in order
- * to avoid the need for any locks.
+ * threaded.
  */
 void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 {
@@ -1170,6 +1168,46 @@ void set_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
 		fput(old_exe_file);
 }
 
+/**
+ * replace_mm_exe_file - replace a reference to the mm's executable file
+ *
+ * This changes mm's executable file (shown as symlink /proc/[pid]/exe),
+ * dealing with concurrent invocation and without grabbing the mmap lock in
+ * write mode.
+ *
+ * Main user is sys_prctl(PR_SET_MM_MAP/EXE_FILE).
+ */
+int replace_mm_exe_file(struct mm_struct *mm, struct file *new_exe_file)
+{
+	struct vm_area_struct *vma;
+	struct file *old_exe_file;
+	int ret = 0;
+
+	/* Forbid mm->exe_file change if old file still mapped. */
+	old_exe_file = get_mm_exe_file(mm);
+	if (old_exe_file) {
+		mmap_read_lock(mm);
+		for (vma = mm->mmap; vma && !ret; vma = vma->vm_next) {
+			if (!vma->vm_file)
+				continue;
+			if (path_equal(&vma->vm_file->f_path,
+				       &old_exe_file->f_path))
+				ret = -EBUSY;
+		}
+		mmap_read_unlock(mm);
+		fput(old_exe_file);
+		if (ret)
+			return ret;
+	}
+
+	/* set the new file, lockless */
+	get_file(new_exe_file);
+	old_exe_file = xchg(&mm->exe_file, new_exe_file);
+	if (old_exe_file)
+		fput(old_exe_file);
+	return 0;
+}
+
 /**
  * get_mm_exe_file - acquire a reference to the mm's executable file
  *
diff --git a/kernel/sys.c b/kernel/sys.c
index ef1a78f5d71c..30c12e54585a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1846,7 +1846,6 @@ SYSCALL_DEFINE1(umask, int, mask)
 static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
 {
 	struct fd exe;
-	struct file *old_exe, *exe_file;
 	struct inode *inode;
 	int err;
 
@@ -1869,40 +1868,10 @@ static int prctl_set_mm_exe_file(struct mm_struct *mm, unsigned int fd)
 	if (err)
 		goto exit;
 
-	/*
-	 * Forbid mm->exe_file change if old file still mapped.
-	 */
-	exe_file = get_mm_exe_file(mm);
-	err = -EBUSY;
-	if (exe_file) {
-		struct vm_area_struct *vma;
-
-		mmap_read_lock(mm);
-		for (vma = mm->mmap; vma; vma = vma->vm_next) {
-			if (!vma->vm_file)
-				continue;
-			if (path_equal(&vma->vm_file->f_path,
-				       &exe_file->f_path))
-				goto exit_err;
-		}
-
-		mmap_read_unlock(mm);
-		fput(exe_file);
-	}
-
-	err = 0;
-	/* set the new file, lockless */
-	get_file(exe.file);
-	old_exe = xchg(&mm->exe_file, exe.file);
-	if (old_exe)
-		fput(old_exe);
+	err = replace_mm_exe_file(mm, exe.file);
 exit:
 	fdput(exe);
 	return err;
-exit_err:
-	mmap_read_unlock(mm);
-	fput(exe_file);
-	goto exit;
 }
 
 /*
-- 
2.31.1


  parent reply	other threads:[~2021-08-16 19:50 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-16 19:48 [PATCH v2 0/7] Remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-16 19:48 ` [PATCH v2 1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib() David Hildenbrand
2021-09-05 15:32   ` Guenter Roeck
2021-09-05 17:17     ` Linus Torvalds
2021-09-05 19:07       ` David Hildenbrand
2021-08-16 19:48 ` David Hildenbrand [this message]
2021-08-19 20:51   ` [PATCH v2 2/7] kernel/fork: factor out replacing the current MM exe_file Linus Torvalds
2021-08-20  8:46     ` David Hildenbrand
2021-08-20 14:36       ` Eric W. Biederman
2021-08-22 17:58         ` Linus Torvalds
2021-08-16 19:48 ` [PATCH v2 3/7] kernel/fork: always deny write access to " David Hildenbrand
2021-08-16 19:48 ` [PATCH v2 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE David Hildenbrand
2021-08-16 19:48 ` [PATCH v2 5/7] mm: remove VM_DENYWRITE David Hildenbrand
2021-08-16 19:48 ` [PATCH v2 6/7] mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff() David Hildenbrand
2021-08-16 19:48 ` [PATCH v2 7/7] fs: update documentation of get_write_access() and friends David Hildenbrand
2021-08-17 11:01 ` [PATCH v2 0/7] Remove in-tree usage of MAP_DENYWRITE Christian König
2021-09-03  9:45 ` David Hildenbrand
2021-09-03 16:26   ` Linus Torvalds

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