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SubjectRe: [PATCH] mm/nommu.c: Fix improperly call of security API in mmap
Date
<graff.yang@gmail.com> wrote:

> The original code calling security_file_mmap() use user's hint address
> as it's 5th argument(addr). This is improper, as the hint address may be
> NULL.
> In this case, the security_file_mmap() may incorrectly return -EPERM.
>
> This patch moved the calling of security_file_mmap() out of
> validate_mmap_request() to do_mmap_pgoff(), and call this
> security API with the address that attempting to mmap.

I think this is the wrong approach. Firstly, the hint is cleared in NOMMU
mode, and secondly, I think that the check against the minimum LSM address is
pointless in NOMMU mode too.

So I think the attached patch is a better approach.

David
---
From: David Howells <dhowells@redhat.com>
NOMMU: Ignore the address parameter in the file_mmap() security check

Ignore the address parameter in the various file_mmap() security checks when
CONFIG_MMU=n as the address hint is ignored under those circumstances, and in
any case the minimum mapping address check is pointless in NOMMU mode.

Signed-off-by: David Howells <dhowells@redhat.com>
---
include/linux/security.h | 1 +
mm/nommu.c | 2 +-
security/commoncap.c | 2 ++
security/selinux/hooks.c | 2 ++
4 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index 239e40d..0583f16 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -593,6 +593,7 @@ static inline void security_free_mnt_opts(struct security_mnt_opts *opts)
* @reqprot contains the protection requested by the application.
* @prot contains the protection that will be applied by the kernel.
* @flags contains the operational flags.
+ * @addr contains the mapping address, and should be ignored in NOMMU mode.
* Return 0 if permission is granted.
* @file_mprotect:
* Check permissions before changing memory access permissions.
diff --git a/mm/nommu.c b/mm/nommu.c
index 3c3b4b2..cfea46c 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -974,7 +974,7 @@ static int validate_mmap_request(struct file *file,
}

/* allow the security API to have its say */
- ret = security_file_mmap(file, reqprot, prot, flags, addr, 0);
+ ret = security_file_mmap(file, reqprot, prot, flags, 0, 0);
if (ret < 0)
return ret;

diff --git a/security/commoncap.c b/security/commoncap.c
index fe30751..ac1f745 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -1005,6 +1005,7 @@ int cap_file_mmap(struct file *file, unsigned long reqprot,
{
int ret = 0;

+#ifdef CONFIG_MMU
if (addr < dac_mmap_min_addr) {
ret = cap_capable(current, current_cred(), CAP_SYS_RAWIO,
SECURITY_CAP_AUDIT);
@@ -1012,5 +1013,6 @@ int cap_file_mmap(struct file *file, unsigned long reqprot,
if (ret == 0)
current->flags |= PF_SUPERPRIV;
}
+#endif
return ret;
}
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index bb230d5..93d61f8 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3046,6 +3046,7 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
unsigned long addr, unsigned long addr_only)
{
int rc = 0;
+#ifdef CONFIG_MMU
u32 sid = current_sid();

/*
@@ -3060,6 +3061,7 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
if (rc)
return rc;
}
+#endif

/* do DAC check on address space usage */
rc = cap_file_mmap(file, reqprot, prot, flags, addr, addr_only);

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