ipc,shm: Correct error return value in shmctl (SHM_UNLOCK)

PATCH In review Jesper Nilsson 2 participants 3 messages Nov 20, 2013 – Nov 24, 2013 Stable branch

Share & tools

Jesper Nilsson

author

2013-11-20 10:44 UTC #0 lore raw

PATCH 1/1 ipc,shm: Correct error return value in shmctl (SHM_UNLOCK)

Commit 2caacaa82a51b78fc0c800e206473874094287ed restructured the ipc shm to shorten critical region, but introduced a path where the return value could be -EPERM, even if the operation actually was performed.

Before the commit, the err return value was reset by the return value from security_shm_shmctl() after the if (!ns_capable(...)) statement.

Now, we still exit the if statement with err set to -EPERM, and in the case of SHM_UNLOCK, it is not reset at all, and used as the return value from shmctl.

To fix this, we only set err when errors occur, leaving the fallthrough case alone.

Signed-off-by Jesper Nilsson <[email protected]>

Cc Andrew Morton <[email protected]>

Cc Davidlohr Bueso <[email protected]>

Cc Rik van Riel <[email protected]>

Cc Michel Lespinasse <[email protected]>

Cc Al Viro <[email protected]>

Cc [email protected]

---
 ipc/shm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

ipc/shm.c +6 -3

index d697396..4076f9e 100644
@@ -974,12 +974,15 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
 		ipc_lock_object(&shp->shm_perm);
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
 			kuid_t euid = current_euid();
-			err = -EPERM;
 			if (!uid_eq(euid, shp->shm_perm.uid) &&
-			    !uid_eq(euid, shp->shm_perm.cuid))
+			    !uid_eq(euid, shp->shm_perm.cuid)) {
+				err = -EPERM;
 				goto out_unlock0;
-			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
+			}
+			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
+				err = -EPERM;
 				goto out_unlock0;
+			}
 		}
 
 		shm_file = shp->shm_file;

Signature · 6 lines

1.8.4


/^JN - Jesper Nilsson
-- 
               Jesper Nilsson -- [email protected]

Mike Galbraith

2013-11-24 07:07 UTC #1 lore raw

This patch (commit: 3a72660b07) is only slated for stable 3.12, but should go to 3.10/11 as well, no?

Quoted 54 lines · Jesper Nilsson

Commit 2caacaa82a51b78fc0c800e206473874094287ed restructured the ipc shm to shorten critical region, but introduced a path where the return value could be -EPERM, even if the operation actually was performed.
Before the commit, the err return value was reset by the return value from security_shm_shmctl() after the if (!ns_capable(...)) statement.
Now, we still exit the if statement with err set to -EPERM, and in the case of SHM_UNLOCK, it is not reset at all, and used as the return value from shmctl.
To fix this, we only set err when errors occur, leaving the fallthrough case alone.
Signed-off-by Jesper Nilsson <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Davidlohr Bueso <[email protected]>
Cc Rik van Riel <[email protected]>
Cc Michel Lespinasse <[email protected]>
Cc Al Viro <[email protected]>
Cc [email protected]
---
 ipc/shm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
ipc/shm.c +6 -3
index d697396..4076f9e 100644
@@ -974,12 +974,15 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
 		ipc_lock_object(&shp->shm_perm);
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
 			kuid_t euid = current_euid();
-			err = -EPERM;
 			if (!uid_eq(euid, shp->shm_perm.uid) &&
-			    !uid_eq(euid, shp->shm_perm.cuid))
+			    !uid_eq(euid, shp->shm_perm.cuid)) {
+				err = -EPERM;
 				goto out_unlock0;
-			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
+			}
+			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
+				err = -EPERM;
 				goto out_unlock0;
+			}
 		}
 
 		shm_file = shp->shm_file;
Signature · 4 lines
1.8.4


/^JN - Jesper Nilsson

Jesper Nilsson

author

2013-11-24 08:54 UTC #2 lore raw

Quoted 2 lines · Mike Galbraith

This patch (commit: 3a72660b07) is only slated for stable 3.12, but should go to 3.10/11 as well, no?

Yes, you're right, both 3.10 and 3.11 seem to have the restructuring patch included (3.10.17 and 3.11.6 respectively), and so should have this patch also.

Quoted 49 lines · Jesper Nilsson

Quoted 48 lines
Commit 2caacaa82a51b78fc0c800e206473874094287ed restructured the ipc shm to shorten critical region, but introduced a path where the return value could be -EPERM, even if the operation actually was performed.
Before the commit, the err return value was reset by the return value from security_shm_shmctl() after the if (!ns_capable(...)) statement.
Now, we still exit the if statement with err set to -EPERM, and in the case of SHM_UNLOCK, it is not reset at all, and used as the return value from shmctl.
To fix this, we only set err when errors occur, leaving the fallthrough case alone.
Signed-off-by Jesper Nilsson <[email protected]>
Cc Andrew Morton <[email protected]>
Cc Davidlohr Bueso <[email protected]>
Cc Rik van Riel <[email protected]>
Cc Michel Lespinasse <[email protected]>
Cc Al Viro <[email protected]>
Cc [email protected]
---
 ipc/shm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)
ipc/shm.c +6 -3
index d697396..4076f9e 100644
@@ -974,12 +974,15 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
 		ipc_lock_object(&shp->shm_perm);
 		if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
 			kuid_t euid = current_euid();
-			err = -EPERM;
 			if (!uid_eq(euid, shp->shm_perm.uid) &&
-			    !uid_eq(euid, shp->shm_perm.cuid))
+			    !uid_eq(euid, shp->shm_perm.cuid)) {
+				err = -EPERM;
 				goto out_unlock0;
-			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK))
+			}
+			if (cmd == SHM_LOCK && !rlimit(RLIMIT_MEMLOCK)) {
+				err = -EPERM;
 				goto out_unlock0;
+			}
 		}
 

Quoted 8 lines

Quoted 6 lines
ipc/shm.c +0 -0
 		shm_file = shp->shm_file;
Signature · 4 lines
1.8.4


/^JN - Jesper Nilsson

/^JN - Jesper Nilsson

Signature · 1 line

               Jesper Nilsson -- [email protected]