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authorDavid Hildenbrand <david@redhat.com>2021-04-23 09:42:41 +0200
committerDavid Hildenbrand <david@redhat.com>2021-09-03 18:42:01 +0200
commit4589ff7ca81516381393649dec8dd4948884b2b2 (patch)
tree4bc5abab9bb7293f60d8b46dea87fb8e4097ae98 /fs/binfmt_aout.c
parentfe69d560b5bd9ec77b5d5749bd7027344daef47e (diff)
binfmt: remove in-tree usage of MAP_DENYWRITE
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> Acked-by: Christian König <christian.koenig@amd.com> Signed-off-by: David Hildenbrand <david@redhat.com>
Diffstat (limited to 'fs/binfmt_aout.c')
-rw-r--r--fs/binfmt_aout.c5
1 files changed, 2 insertions, 3 deletions
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;