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    SubjectRe: [PATCH] mm/nommu.c: Fix improperly call of security API in mmap
    On Fri, 16 Oct 2009 11:55:29 -0400
    Eric Paris <eparis@redhat.com> wrote:

    > On Fri, 2009-10-16 at 16:43 +0100, David Howells wrote:
    > > Eric Paris <eparis@redhat.com> wrote:
    > >
    > > > That would still call cap_file_mmap() and wouldn't solve your problem.
    > >
    > > Hmmm... I guess I don't see the problem occur because I always run the
    > > programs as root.
    >
    > most likely yes, your processes are going to have CAP_SYS_RAWIO and will
    > happily sail through the cap_file_mmap().
    >
    > > I would guess that cap_file_mmap() and selinux_file_mmap() are, perhaps, too
    > > strict. The hint shouldn't be rejected unless MAP_FIXED is also set, surely,
    > > but should rather be revised upwards.
    >
    > On the mmu side we don't check until the kernel has turned the hint into
    > a real address. Which is apparently different then where the hook was
    > originally placed in the nommu side.
    >
    > > Certainly, addr==NULL and !MAP_FIXED is a reasonable case to permit, even in
    > > tightly secured MMU and SELinux mode... After all, the manual page says:
    > >
    > > If addr is NULL, then the kernel chooses the address at which to create
    > > the mapping; this is the most portable method of creating a new map-
    > > ping.
    >
    > I agree, I think the choices are
    >
    > A) agree that we just shouldn't check the address on nommu
    > A1) change kconfig to not allow the setting of these
    > (easy to do for the LSM check, but not easy as it stands today
    > for the cap_file_mmap() check)
    > A2) change the addr_only to be a flags which indicate not to check
    > (my original suggestion)
    > A3) push the config_nommu down into the security code
    > (your patch)
    > B) actually check the address, which requires moving the hook to a
    > location where it has been resolved.
    > (graff yang's patch)
    >
    > I'll leave it up to you to determine which you like the best since you
    > know the implications of nommu.
    >

    So what's the status of this issue now? Should I merge the below into
    2.6.32?

    Thanks.



    From: David Howells <dhowells@redhat.com>

    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>
    Reported-by: Graff Yang <graf.yang@analog.com>
    Cc: James Morris <jmorris@namei.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    ---

    include/linux/security.h | 1 +
    mm/nommu.c | 2 +-
    security/commoncap.c | 2 ++
    security/selinux/hooks.c | 2 ++
    4 files changed, 6 insertions(+), 1 deletion(-)

    diff -puN include/linux/security.h~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check include/linux/security.h
    --- a/include/linux/security.h~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check
    +++ a/include/linux/security.h
    @@ -609,6 +609,7 @@ static inline void security_free_mnt_opt
    * @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 -puN mm/nommu.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check mm/nommu.c
    --- a/mm/nommu.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check
    +++ a/mm/nommu.c
    @@ -974,7 +974,7 @@ static int validate_mmap_request(struct
    }

    /* 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 -puN security/commoncap.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check security/commoncap.c
    --- a/security/commoncap.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check
    +++ a/security/commoncap.c
    @@ -1005,6 +1005,7 @@ int cap_file_mmap(struct file *file, uns
    {
    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, uns
    if (ret == 0)
    current->flags |= PF_SUPERPRIV;
    }
    +#endif
    return ret;
    }
    diff -puN security/selinux/hooks.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check security/selinux/hooks.c
    --- a/security/selinux/hooks.c~nommu-ignore-the-address-parameter-in-the-file_mmap-security-check
    +++ a/security/selinux/hooks.c
    @@ -3046,6 +3046,7 @@ static int selinux_file_mmap(struct file
    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
    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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