diff mbox series

[RFC,1/7] binfmt: don't use MAP_DENYWRITE when loading shared libraries via uselib()

Message ID 20210423131640.20080-2-david@redhat.com (mailing list archive)
State New, archived
Headers show
Series Remove in-tree usage of MAP_DENYWRITE | expand

Commit Message

David Hildenbrand April 23, 2021, 1:16 p.m. UTC 
uselib() is the legacy systemcall for loading shared libraries.
Nowadays, applications use dlopen() to load shared libraries, completely
implemented in user space via mmap().

For example, glibc uses MAP_COPY to mmap shared libraries. While this
maps to MAP_PRIVATE | MAP_DENYWRITE on Linux, Linux ignores any
MAP_DENYWRITE specification from user space in mmap.

With this change, all remaining in-tree users of MAP_DENYWRITE use it
to map an executable. We will be able to open shared libraries loaded
via uselib() writable, just as we already can via dlopen() from user
space.

This is one step into the direction of removing MAP_DENYWRITE from the
kernel. This can be considered a minor user space visible change.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/x86/ia32/ia32_aout.c | 2 +-
 fs/binfmt_aout.c          | 2 +-
 fs/binfmt_elf.c           | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c
index 5e5b9fc2747f..321d7b22ad2d 100644
--- a/arch/x86/ia32/ia32_aout.c
+++ b/arch/x86/ia32/ia32_aout.c
@@ -293,7 +293,7 @@  static int load_aout_library(struct file *file)
 	/* Now use mmap to map the library into memory. */
 	error = vm_mmap(file, start_addr, ex.a_text + ex.a_data,
 			PROT_READ | PROT_WRITE | PROT_EXEC,
-			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE | MAP_32BIT,
+			MAP_FIXED | MAP_PRIVATE | MAP_32BIT,
 			N_TXTOFF(ex));
 	retval = error;
 	if (error != start_addr)
diff --git a/fs/binfmt_aout.c b/fs/binfmt_aout.c
index 12461f3ed04f..37df8fee63d7 100644
--- a/fs/binfmt_aout.c
+++ b/fs/binfmt_aout.c
@@ -309,7 +309,7 @@  static int load_aout_library(struct file *file)
 	/* Now use mmap to map the library into memory. */
 	error = vm_mmap(file, start_addr, ex.a_text + ex.a_data,
 			PROT_READ | PROT_WRITE | PROT_EXEC,
-			MAP_FIXED | MAP_PRIVATE | MAP_DENYWRITE,
+			MAP_FIXED | MAP_PRIVATE;
 			N_TXTOFF(ex));
 	retval = error;
 	if (error != start_addr)
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index e0427b817425..763188ac398e 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1384,7 +1384,7 @@  static int load_elf_library(struct file *file)
 			(eppnt->p_filesz +
 			 ELF_PAGEOFFSET(eppnt->p_vaddr)),
 			PROT_READ | PROT_WRITE | PROT_EXEC,
-			MAP_FIXED_NOREPLACE | MAP_PRIVATE | MAP_DENYWRITE,
+			MAP_FIXED_NOREPLACE | MAP_PRIVATE,
 			(eppnt->p_offset -
 			 ELF_PAGEOFFSET(eppnt->p_vaddr)));
 	if (error != ELF_PAGESTART(eppnt->p_vaddr))