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mm: reorder can_do_mlock to fix audit denial

PATCH In review Jeff Vander Stoep 3 participants 4 messages Mar 2, 2015 – Mar 3, 2015

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Jeff Vander Stoep

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#0 lore raw

PATCH 1/1 mm: reorder can_do_mlock to fix audit denial

A userspace call to mmap(MAP_LOCKED) may result in the successful locking of memory while also producing a confusing audit log denial. can_do_mlock checks capable and rlimit. If either of these return positive can_do_mlock returns true. The capable check leads to an LSM hook used by apparmour and selinux which produce the audit denial. Reordering so rlimit is checked first eliminates the denial on success, only recording a denial when the lock is unsuccessful as a result of the denial.

Signed-off-by Jeff Vander Stoep <[email protected]>
---
 mm/mlock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
mm/mlock.c +2 -2
index 73cf098..8a54cd2 100644
@@ -26,10 +26,10 @@
 
 int can_do_mlock(void)
 {
-	if (capable(CAP_IPC_LOCK))
-		return 1;
 	if (rlimit(RLIMIT_MEMLOCK) != 0)
 		return 1;
+	if (capable(CAP_IPC_LOCK))
+		return 1;
 	return 0;
 }
 EXPORT_SYMBOL(can_do_mlock);
Signature · 7 lines
2.2.0.rc0.207.ga3a616c

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Acked-by on v1 1/1
#1 lore raw
Quoted 9 lines · Jeff Vander Stoep

A userspace call to mmap(MAP_LOCKED) may result in the successful locking of memory while also producing a confusing audit log denial. can_do_mlock checks capable and rlimit. If either of these return positive can_do_mlock returns true. The capable check leads to an LSM hook used by apparmour and selinux which produce the audit denial. Reordering so rlimit is checked first eliminates the denial on success, only recording a denial when the lock is unsuccessful as a result of the denial.

Acked-by Nick Kralevich <[email protected]>
Quoted 25 lines
Signed-off-by Jeff Vander Stoep <[email protected]>
---
 mm/mlock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
mm/mlock.c +2 -3
index 73cf098..8a54cd2 100644
@@ -26,10 +26,10 @@
 
 int can_do_mlock(void)
 {
-       if (capable(CAP_IPC_LOCK))
-               return 1;
        if (rlimit(RLIMIT_MEMLOCK) != 0)
                return 1;
+       if (capable(CAP_IPC_LOCK))
+               return 1;
        return 0;
 }
 EXPORT_SYMBOL(can_do_mlock);
--

2.2.0.rc0.207.ga3a616c

Signature · 7 lines
Nick Kralevich | Android Security | [email protected] | 650.214.4037

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maintainer
#2 lore raw
In reply to Jeff Vander Stoep
Quoted 8 lines · On Mon, 2 Mar 2015 09:20:32 -0800 Jeff Vander Stoep <[email protected]> wrote:

A userspace call to mmap(MAP_LOCKED) may result in the successful locking of memory while also producing a confusing audit log denial. can_do_mlock checks capable and rlimit. If either of these return positive can_do_mlock returns true. The capable check leads to an LSM hook used by apparmour and selinux which produce the audit denial. Reordering so rlimit is checked first eliminates the denial on success, only recording a denial when the lock is unsuccessful as a result of the denial.

I'm assuming that this is a minor issue - a bogus audit log, no other consequences. And based on this I queued the patch for 4.0 with no -stable backport.

All of this might have been wrong - the changelog wasn't very helpful in making such decisions (hint).

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author
#3 lore raw

Yes, minor issue.

I appreciate the advice.

Quoted 11 lines · Andrew Morton
Quoted 8 lines · On Mon, 2 Mar 2015 09:20:32 -0800 Jeff Vander Stoep <[email protected]> wrote:

A userspace call to mmap(MAP_LOCKED) may result in the successful locking of memory while also producing a confusing audit log denial. can_do_mlock checks capable and rlimit. If either of these return positive can_do_mlock returns true. The capable check leads to an LSM hook used by apparmour and selinux which produce the audit denial. Reordering so rlimit is checked first eliminates the denial on success, only recording a denial when the lock is unsuccessful as a result of the denial.

Quoted 6 lines

I'm assuming that this is a minor issue - a bogus audit log, no other consequences. And based on this I queued the patch for 4.0 with no -stable backport.

All of this might have been wrong - the changelog wasn't very helpful in making such decisions (hint).

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