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Message-Id: <20210816194840.42769-3-david@redhat.com>
Date: Mon, 16 Aug 2021 21:48:35 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: David Hildenbrand <david@...hat.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Alexey Dobriyan <adobriyan@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Kees Cook <keescook@...omium.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Greg Ungerer <gerg@...ux-m68k.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Mike Rapoport <rppt@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Chinwen Chang <chinwen.chang@...iatek.com>,
Catalin Marinas <catalin.marinas@....com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Huang Ying <ying.huang@...el.com>,
Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
Kevin Brodsky <Kevin.Brodsky@....com>,
Michael Ellerman <mpe@...erman.id.au>,
Shawn Anastasio <shawn@...stas.io>,
Steven Price <steven.price@....com>,
Nicholas Piggin <npiggin@...il.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Jens Axboe <axboe@...nel.dk>,
Gabriel Krisman Bertazi <krisman@...labora.com>,
Peter Xu <peterx@...hat.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
Marco Elver <elver@...gle.com>,
Daniel Jordan <daniel.m.jordan@...cle.com>,
Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
Thomas Cedeno <thomascedeno@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Miklos Szeredi <miklos@...redi.hu>,
Chengguang Xu <cgxu519@...ernel.net>,
Christian König
<ckoenig.leichtzumerken@...il.com>,
Florian Weimer <fweimer@...hat.com>,
David Laight <David.Laight@...LAB.COM>,
linux-unionfs@...r.kernel.org, linux-api@...r.kernel.org,
x86@...nel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH v2 2/7] kernel/fork: factor out replacing the current MM exe_file
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@...ntu.com>
Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: David Hildenbrand <david@...hat.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
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