[PATCH] seccomp: Release fp pointer when leaving from seccomp_attach_filter().

[Masami Ichikawa <masami256@gmail.com>]

kmemleak reported some memory leak as below.

unreferenced object 0xffff8800d6ea4000 (size 512):
  comm "sshd", pid 278, jiffies 4294898315 (age 46.653s)
  hex dump (first 32 bytes):
    21 00 00 00 04 00 00 00 15 00 01 00 3e 00 00 c0  !...........>...
    06 00 00 00 00 00 00 00 21 00 00 00 00 00 00 00  ........!.......
  backtrace:
    [<ffffffff8151414e>] kmemleak_alloc+0x4e/0xb0
    [<ffffffff811a3a40>] __kmalloc+0x280/0x320
    [<ffffffff8110842e>] prctl_set_seccomp+0x11e/0x3b0
    [<ffffffff8107bb6b>] SyS_prctl+0x3bb/0x4a0
    [<ffffffff8152ef2d>] system_call_fastpath+0x1a/0x1f
    [<ffffffffffffffff>] 0xffffffffffffffff

This memory leak happend in seccomp_attach_filter().
The fp pointer was allocated via kzalloc so that it needs to realase memory
when leaving from function.

This patch changed two things.
One is set -ENOMEM to ret, if fp is unable to get memory.
The other is removes "return 0" statement, and frees fp pointer before
leaving.

Signed-off-by: Masami Ichikawa <masami256@gmail.com>
---
 kernel/seccomp.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index d8d046c..a9ce7a9 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -259,8 +259,10 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
 	filter = kzalloc(sizeof(struct seccomp_filter) +
 			 sizeof(struct sock_filter_int) * new_len,
 			 GFP_KERNEL|__GFP_NOWARN);
-	if (!filter)
+	if (!filter) {
+		ret = -ENOMEM;
 		goto free_prog;
+	}
 
 	ret = sk_convert_filter(fp, fprog->len, filter->insnsi, &new_len);
 	if (ret)
@@ -275,10 +277,10 @@ static long seccomp_attach_filter(struct sock_fprog *fprog)
 	 */
 	filter->prev = current->seccomp.filter;
 	current->seccomp.filter = filter;
-	return 0;
 
 free_filter:
-	kfree(filter);
+	if (ret)
+		kfree(filter);
 free_prog:
 	kfree(fp);
 	return ret;
-- 
1.9.1