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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 4/7] binfmt: remove in-tree usage of MAP_DENYWRITE
Date: Mon, 16 Aug 2021 21:48:37 +0200	[thread overview]
Message-ID: <20210816194840.42769-5-david@redhat.com> (raw)
In-Reply-To: <20210816194840.42769-1-david@redhat.com>

At exec time when we mmap the new executable via MAP_DENYWRITE we have it
opened via do_open_execat() and already deny_write_access()'ed the file
successfully. Once exec completes, we allow_write_acces(); however,
we set mm->exe_file in begin_new_exec() via set_mm_exe_file() and
also deny_write_access() as long as mm->exe_file remains set. We'll
effectively deny write access to our executable via mm->exe_file
until mm->exe_file is changed -- when the process is removed, on new
exec, or via sys_prctl(PR_SET_MM_MAP/EXE_FILE).

Let's remove all usage of MAP_DENYWRITE, it's no longer necessary for
mm->exe_file.

In case of an elf interpreter, we'll now only deny write access to the file
during exec. This is somewhat okay, because the interpreter behaves
(and sometime is) a shared library; all shared libraries, especially the
ones loaded directly in user space like via dlopen() won't ever be mapped
via MAP_DENYWRITE, because we ignore that from user space completely;
these shared libraries can always be modified while mapped and executed.
Let's only special-case the main executable, denying write access while
being executed by a process. This can be considered a minor user space
visible change.

While this is a cleanup, it also fixes part of a problem reported with
VM_DENYWRITE on overlayfs, as VM_DENYWRITE is effectively unused with
this patch and will be removed next:
  "Overlayfs did not honor positive i_writecount on realfile for
   VM_DENYWRITE mappings." [1]

[1] https://lore.kernel.org/r/YNHXzBgzRrZu1MrD@miu.piliscsaba.redhat.com/

Reported-by: Chengguang Xu <cgxu519@mykernel.net>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/x86/ia32/ia32_aout.c | 6 ++----
 fs/binfmt_aout.c          | 5 ++---
 fs/binfmt_elf.c           | 4 ++--
 fs/binfmt_elf_fdpic.c     | 2 +-
 4 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index 321d7b22ad2d..9bd15241fadb 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -202,8 +202,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
 
 		error = vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
 				PROT_READ | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE |
-				MAP_32BIT,
+				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
 				fd_offset);
 
 		if (error != N_TXTADDR(ex))
@@ -211,8 +210,7 @@ static int load_aout_binary(struct linux_binprm *bprm)
 
 		error = vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
 				PROT_READ | PROT_WRITE | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE |
-				MAP_32BIT,
+				MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
 				fd_offset + ex.a_text);
 		if (error != N_DATADDR(ex))
 			return error;
diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index d29de971d3f3..a47496d0f123 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -221,8 +221,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
 		}
 
 		error = vm_mmap(bprm->file, N_TXTADDR(ex), ex.a_text,
-			PROT_READ | PROT_EXEC,
-			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE,
+			PROT_READ | PROT_EXEC, MAP_FIXED | MAP_PRIVATE,
 			fd_offset);
 
 		if (error != N_TXTADDR(ex))
@@ -230,7 +229,7 @@ static int load_aout_binary(struct linux_binprm * bprm)
 
 		error = vm_mmap(bprm->file, N_DATADDR(ex), ex.a_data,
 				PROT_READ | PROT_WRITE | PROT_EXEC,
-				MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE,
+				MAP_FIXED | MAP_PRIVATE,
 				fd_offset + ex.a_text);
 		if (error != N_DATADDR(ex))
 			return error;
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 6d2c79533631..69d900a8473d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -622,7 +622,7 @@ static unsigned long load_elf_interp(struct elfhdr *interp_elf_ex,
 	eppnt = interp_elf_phdata;
 	for (i = 0; i < interp_elf_ex->e_phnum; i++, eppnt++) {
 		if (eppnt->p_type == PT_LOAD) {
-			int elf_type = MAP_PRIVATE | MAP_DENYWRITE;
+			int elf_type = MAP_PRIVATE;
 			int elf_prot = make_prot(eppnt->p_flags, arch_state,
 						 true, true);
 			unsigned long vaddr = 0;
@@ -1070,7 +1070,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 		elf_prot = make_prot(elf_ppnt->p_flags, &arch_state,
 				     !!interpreter, false);
 
-		elf_flags = MAP_PRIVATE | MAP_DENYWRITE;
+		elf_flags = MAP_PRIVATE;
 
 		vaddr = elf_ppnt->p_vaddr;
 		/*
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index cf4028487dcc..6d8fd6030cbb 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -1041,7 +1041,7 @@ static int elf_fdpic_map_file_by_direct_mmap(struct elf_fdpic_params *params,
 		if (phdr->p_flags & PF_W) prot |= PROT_WRITE;
 		if (phdr->p_flags & PF_X) prot |= PROT_EXEC;
 
-		flags = MAP_PRIVATE | MAP_DENYWRITE;
+		flags = MAP_PRIVATE;
 		maddr = 0;
 
 		switch (params->flags & ELF_FDPIC_FLAG_ARRANGEMENT) {
-- 
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 " 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 ` [PATCH v2 2/7] kernel/fork: factor out replacing the current MM exe_file David Hildenbrand
2021-08-19 20:51   ` 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 ` David Hildenbrand [this message]
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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