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@xxxxxxxxxxxxxxxxxxxxxxxxx/ Reported-by: Chengguang Xu <cgxu519@xxxxxxxxxxxx> Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- 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
