Currently non-SELinux systems need CAP_SYS_RAWIO for an application to mmap
the 0 page. On SELinux systems they need a specific SELinux permission,
but do not need CAP_SYS_RAWIO. This has proved to be a poor decision by
the SELinux team as, by default, SELinux users are logged in unconfined and
thus a malicious non-root has nothing stopping them from mapping the 0 page
of virtual memory.
On a non-SELinux system, a malicious non-root user is unable to do this, as
they need CAP_SYS_RAWIO.
This patch checks CAP_SYS_RAWIO for all operations which attemt to map a
page below mmap_min_addr.
Signed-off-by: Eric Paris <eparis@xxxxxxxxxx>
---
include/linux/security.h | 2 --
mm/mmap.c | 10 ++++++++++
mm/mremap.c | 8 ++++++++
mm/nommu.c | 3 +++
security/capability.c | 2 --
5 files changed, 21 insertions(+), 4 deletions(-)
diff --git a/include/linux/security.h b/include/linux/security.h
index 1459091..f7d198a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2197,8 +2197,6 @@ static inline int security_file_mmap(struct file *file, unsigned long reqprot,
unsigned long addr,
unsigned long addr_only)
{
- if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
- return -EACCES;
return 0;
}
diff --git a/mm/mmap.c b/mm/mmap.c
index 34579b2..37fdc90 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1047,6 +1047,9 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned long addr,
}
}
+ if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ return -EACCES;
+
error = security_file_mmap(file, reqprot, prot, flags, addr, 0);
if (error)
return error;
@@ -1657,6 +1660,10 @@ static int expand_downwards(struct vm_area_struct *vma,
return -ENOMEM;
address &= PAGE_MASK;
+
+ if ((address < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ return -EACCES;
+
error = security_file_mmap(NULL, 0, 0, 0, address, 1);
if (error)
return error;
@@ -1998,6 +2005,9 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
if (is_hugepage_only_range(mm, addr, len))
return -EINVAL;
+ if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ return -EACCES;
+
error = security_file_mmap(NULL, 0, 0, 0, addr, 1);
if (error)
return error;
diff --git a/mm/mremap.c b/mm/mremap.c
index a39b7b9..066e73d 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -299,6 +299,10 @@ unsigned long do_mremap(unsigned long addr,
if ((addr <= new_addr) && (addr+old_len) > new_addr)
goto out;
+ ret = -EACCES;
+ if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ goto out;
+
ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
if (ret)
goto out;
@@ -407,6 +411,10 @@ unsigned long do_mremap(unsigned long addr,
goto out;
}
+ ret = -EACCES;
+ if ((new_addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ goto out;
+
ret = security_file_mmap(NULL, 0, 0, 0, new_addr, 1);
if (ret)
goto out;
diff --git a/mm/nommu.c b/mm/nommu.c
index 53cab10..c1f3eff 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -995,6 +995,9 @@ static int validate_mmap_request(struct file *file,
}
/* allow the security API to have its say */
+ if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
+ return -EACCES;
+
ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
if (ret < 0)
return ret;
diff --git a/security/capability.c b/security/capability.c
index f218dd3..a3a5d9b 100644
--- a/security/capability.c
+++ b/security/capability.c
@@ -334,8 +334,6 @@ static int cap_file_mmap(struct file *file, unsigned long reqprot,
unsigned long prot, unsigned long flags,
unsigned long addr, unsigned long addr_only)
{
- if ((addr < mmap_min_addr) && !capable(CAP_SYS_RAWIO))
- return -EACCES;
return 0;
}
--
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