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[1/1] mm: enforce min addr even if capable() in expand_downwards()

Message ID 1551926175-24580-2-git-send-email-tyhicks@canonical.com
State New
Headers show
Series CVE-2019-9213 - Incorrect memory protection check | expand

Commit Message

Tyler Hicks March 7, 2019, 2:36 a.m. UTC 
From: Jann Horn <jannh@google.com>

security_mmap_addr() does a capability check with current_cred(), but
we can reach this code from contexts like a VFS write handler where
current_cred() must not be used.

This can be abused on systems without SMAP to make NULL pointer
dereferences exploitable again.

Fixes: 8869477a49c3 ("security: protect from stack expansion into low vm addresses")
Cc: stable@kernel.org
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

CVE-2019-9213

(cherry picked from commit 0a1d52994d440e21def1c2174932410b4f2a98a1)
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
---
 mm/mmap.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Comments

Kleber Sacilotto de Souza March 7, 2019, 3:36 p.m. UTC | #1 
On 3/7/19 3:36 AM, Tyler Hicks wrote:
> From: Jann Horn <jannh@google.com>
>
> security_mmap_addr() does a capability check with current_cred(), but
> we can reach this code from contexts like a VFS write handler where
> current_cred() must not be used.
>
> This can be abused on systems without SMAP to make NULL pointer
> dereferences exploitable again.
>
> Fixes: 8869477a49c3 ("security: protect from stack expansion into low vm addresses")
> Cc: stable@kernel.org
> Signed-off-by: Jann Horn <jannh@google.com>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
>
> CVE-2019-9213
>
> (cherry picked from commit 0a1d52994d440e21def1c2174932410b4f2a98a1)
> Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

As mentioned on previous messages, this patch doesn't apply cleanly to
trusty, so it needs to be fixed and marked as "(backported from ...)".

Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

> ---
>  mm/mmap.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f189d4b08633..809a5869480f 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2391,12 +2391,11 @@ int expand_downwards(struct vm_area_struct *vma,
>  {
>  	struct mm_struct *mm = vma->vm_mm;
>  	struct vm_area_struct *prev;
> -	int error;
> +	int error = 0;
>  
>  	address &= PAGE_MASK;
> -	error = security_mmap_addr(address);
> -	if (error)
> -		return error;
> +	if (address < mmap_min_addr)
> +		return -EPERM;
>  
>  	/* Enforce stack_guard_gap */
>  	prev = vma->vm_prev;
diff mbox series

Patch

diff --git a/mm/mmap.c b/mm/mmap.c
index f189d4b08633..809a5869480f 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2391,12 +2391,11 @@  int expand_downwards(struct vm_area_struct *vma,
 {
 	struct mm_struct *mm = vma->vm_mm;
 	struct vm_area_struct *prev;
-	int error;
+	int error = 0;
 
 	address &= PAGE_MASK;
-	error = security_mmap_addr(address);
-	if (error)
-		return error;
+	if (address < mmap_min_addr)
+		return -EPERM;
 
 	/* Enforce stack_guard_gap */
 	prev = vma->vm_prev;