install_special_mapping skips security_file_mmap check.
The install_special_mapping routine (used, for example, to setup the vdso) skips the security check before insert_vm_struct, allowing a local attacker to bypass the mmap_min_addr security restriction by limiting the available pages for special mappings. bprm_mm_init() also skips the check, and although I don't think this can be used to bypass any restrictions, I don't see any reason not to have the security check. $ uname -m x86_64 $ cat /proc/sys/vm/mmap_min_addr 65536 $ cat install_special_mapping.s section .bss resb BSS_SIZE section .text global _start _start: mov eax, __NR_pause int 0x80 $ nasm -D__NR_pause=29 -DBSS_SIZE=0xfffed000 -f elf -o install_special_mapping.o install_special_mapping.s $ ld -m elf_i386 -Ttext=0x10000 -Tbss=0x11000 -o install_special_mapping install_special_mapping.o $ ./install_special_mapping & [1] 14303 $ cat /proc/14303/maps 0000f000-00010000 r-xp 00000000 00:00 0 [vdso] 00010000-00011000 r-xp 00001000 00:19 2453665 /home/taviso/install_special_mapping 00011000-ffffe000 rwxp 00000000 00:00 0 [stack] It's worth noting that Red Hat are shipping with mmap_min_addr set to 4096. Signed-off-by: Tavis Ormandy <taviso@google.com> Acked-by: Kees Cook <kees@ubuntu.com> Acked-by: Robert Swiecki <swiecki@google.com> [ Changed to not drop the error code - akpm ] Reviewed-by: James Morris <jmorris@namei.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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parent
0fcdcfbbc9
commit
462e635e5b
2 changed files with 17 additions and 4 deletions
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@ -275,6 +275,11 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
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vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
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vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
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INIT_LIST_HEAD(&vma->anon_vma_chain);
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err = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
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if (err)
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goto err;
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err = insert_vm_struct(mm, vma);
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if (err)
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goto err;
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16
mm/mmap.c
16
mm/mmap.c
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@ -2462,6 +2462,7 @@ int install_special_mapping(struct mm_struct *mm,
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unsigned long addr, unsigned long len,
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unsigned long vm_flags, struct page **pages)
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{
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int ret;
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struct vm_area_struct *vma;
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vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
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@ -2479,16 +2480,23 @@ int install_special_mapping(struct mm_struct *mm,
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vma->vm_ops = &special_mapping_vmops;
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vma->vm_private_data = pages;
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if (unlikely(insert_vm_struct(mm, vma))) {
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kmem_cache_free(vm_area_cachep, vma);
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return -ENOMEM;
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}
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ret = security_file_mmap(NULL, 0, 0, 0, vma->vm_start, 1);
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if (ret)
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goto out;
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ret = insert_vm_struct(mm, vma);
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if (ret)
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goto out;
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mm->total_vm += len >> PAGE_SHIFT;
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perf_event_mmap(vma);
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return 0;
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out:
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kmem_cache_free(vm_area_cachep, vma);
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return ret;
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}
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static DEFINE_MUTEX(mm_all_locks_mutex);
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