netdev - [PATCH] net: sysctl: fix a kmemleak warning

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Date:	Thu, 22 Oct 2015 11:27:12 +0800
From:	roy.qing.li@...il.com
To:	netdev@...r.kernel.org
Subject: [PATCH] net: sysctl: fix a kmemleak warning

From: Li RongQing <roy.qing.li@...il.com>

the returned buffer of register_sysctl() is stored into net_header
variable, but net_header is not used after, and compiler maybe
optimise the variable out, and lead kmemleak reported the below warning

	comm "swapper/0", pid 1, jiffies 4294937448 (age 267.270s)
	hex dump (first 32 bytes):
	90 38 8b 01 c0 ff ff ff 00 00 00 00 01 00 00 00 .8..............
	01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
	backtrace:
	[<ffffffc00020f134>] create_object+0x10c/0x2a0
	[<ffffffc00070ff44>] kmemleak_alloc+0x54/0xa0
	[<ffffffc0001fe378>] __kmalloc+0x1f8/0x4f8
	[<ffffffc00028e984>] __register_sysctl_table+0x64/0x5a0
	[<ffffffc00028eef0>] register_sysctl+0x30/0x40
	[<ffffffc00099c304>] net_sysctl_init+0x20/0x58
	[<ffffffc000994dd8>] sock_init+0x10/0xb0
	[<ffffffc0000842e0>] do_one_initcall+0x90/0x1b8
	[<ffffffc000966bac>] kernel_init_freeable+0x218/0x2f0
	[<ffffffc00070ed6c>] kernel_init+0x1c/0xe8
	[<ffffffc000083bfc>] ret_from_fork+0xc/0x50
	[<ffffffffffffffff>] 0xffffffffffffffff <<end check kmemleak>>

Before fix, the objdump result on ARM64:
0000000000000000 <net_sysctl_init>:
   0:   a9be7bfd        stp     x29, x30, [sp,#-32]!
   4:   90000001        adrp    x1, 0 <net_sysctl_init>
   8:   90000000        adrp    x0, 0 <net_sysctl_init>
   c:   910003fd        mov     x29, sp
  10:   91000021        add     x1, x1, #0x0
  14:   91000000        add     x0, x0, #0x0
  18:   a90153f3        stp     x19, x20, [sp,#16]
  1c:   12800174        mov     w20, #0xfffffff4                // #-12
  20:   94000000        bl      0 <register_sysctl>
  24:   b4000120        cbz     x0, 48 <net_sysctl_init+0x48>
  28:   90000013        adrp    x19, 0 <net_sysctl_init>
  2c:   91000273        add     x19, x19, #0x0
  30:   9101a260        add     x0, x19, #0x68
  34:   94000000        bl      0 <register_pernet_subsys>
  38:   2a0003f4        mov     w20, w0
  3c:   35000060        cbnz    w0, 48 <net_sysctl_init+0x48>
  40:   aa1303e0        mov     x0, x19
  44:   94000000        bl      0 <register_sysctl_root>
  48:   2a1403e0        mov     w0, w20
  4c:   a94153f3        ldp     x19, x20, [sp,#16]
  50:   a8c27bfd        ldp     x29, x30, [sp],#32
  54:   d65f03c0        ret
After:
0000000000000000 <net_sysctl_init>:
   0:   a9bd7bfd        stp     x29, x30, [sp,#-48]!
   4:   90000000        adrp    x0, 0 <net_sysctl_init>
   8:   910003fd        mov     x29, sp
   c:   a90153f3        stp     x19, x20, [sp,#16]
  10:   90000013        adrp    x19, 0 <net_sysctl_init>
  14:   91000000        add     x0, x0, #0x0
  18:   91000273        add     x19, x19, #0x0
  1c:   f90013f5        str     x21, [sp,#32]
  20:   aa1303e1        mov     x1, x19
  24:   12800175        mov     w21, #0xfffffff4                // #-12
  28:   94000000        bl      0 <register_sysctl>
  2c:   f9002260        str     x0, [x19,#64]
  30:   b40001c0        cbz     x0, 68 <net_sysctl_init+0x68>
  34:   90000014        adrp    x20, 0 <net_sysctl_init>
  38:   91000294        add     x20, x20, #0x0
  3c:   9101a280        add     x0, x20, #0x68
  40:   94000000        bl      0 <register_pernet_subsys>
  44:   2a0003f5        mov     w21, w0
  48:   35000080        cbnz    w0, 58 <net_sysctl_init+0x58>
  4c:   aa1403e0        mov     x0, x20
  50:   94000000        bl      0 <register_sysctl_root>
  54:   14000005        b       68 <net_sysctl_init+0x68>
  58:   f9402260        ldr     x0, [x19,#64]
  5c:   94000000        bl      0 <unregister_sysctl_table>
  60:   f9402260        ldr     x0, [x19,#64]
  64:   94000000        bl      0 <kfree>
  68:   2a1503e0        mov     w0, w21
  6c:   f94013f5        ldr     x21, [sp,#32]
  70:   a94153f3        ldp     x19, x20, [sp,#16]
  74:   a8c37bfd        ldp     x29, x30, [sp],#48
  78:   d65f03c0        ret

Add the possible error handle to free the net_header to remove the
kmemleak warning

Signed-off-by: Li RongQing <roy.qing.li@...il.com>
---
 net/sysctl_net.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index e7000be..a5372d2 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -94,10 +94,14 @@ __init int net_sysctl_init(void)
 		goto out;
 	ret = register_pernet_subsys(&sysctl_pernet_ops);
 	if (ret)
-		goto out;
+		goto out1;
 	register_sysctl_root(&net_sysctl_root);
 out:
 	return ret;
+out1:
+	unregister_sysctl_table(net_header);
+	kfree(net_header);
+	goto out;
 }
 
 struct ctl_table_header *register_net_sysctl(struct net *net,
-- 
2.1.4

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