[ 33/48] net: sysctl_net_core: check SNDBUF and RCVBUF for min length

[Willy Tarreau <w@1wt.eu>]

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Kodanev <alexey.kodanev@oracle.com>

[ Upstream commit b1cb59cf2efe7971d3d72a7b963d09a512d994c9 ]

sysctl has sysctl.net.core.rmem_*/wmem_* parameters which can be
set to incorrect values. Given that 'struct sk_buff' allocates from
rcvbuf, incorrectly set buffer length could result to memory
allocation failures. For example, set them as follows:

    # sysctl net.core.rmem_default=64
      net.core.wmem_default = 64
    # sysctl net.core.wmem_default=64
      net.core.wmem_default = 64
    # ping localhost -s 1024 -i 0 > /dev/null

This could result to the following failure:

skbuff: skb_over_panic: text:ffffffff81628db4 len:-32 put:-32
head:ffff88003a1cc200 data:ffff88003a1cc200 tail:0xffffffe0 end:0xc0 dev:<NULL>
kernel BUG at net/core/skbuff.c:102!
invalid opcode: 0000 [#1] SMP
...
task: ffff88003b7f5550 ti: ffff88003ae88000 task.ti: ffff88003ae88000
RIP: 0010:[<ffffffff8155fbd1>]  [<ffffffff8155fbd1>] skb_put+0xa1/0xb0
RSP: 0018:ffff88003ae8bc68  EFLAGS: 00010296
RAX: 000000000000008d RBX: 00000000ffffffe0 RCX: 0000000000000000
RDX: ffff88003fdcf598 RSI: ffff88003fdcd9c8 RDI: ffff88003fdcd9c8
RBP: ffff88003ae8bc88 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 00000000000002b2 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88003d3f7300 R15: ffff88000012a900
FS:  00007fa0e2b4a840(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000d0f7e0 CR3: 000000003b8fb000 CR4: 00000000000006f0
Stack:
 ffff88003a1cc200 00000000ffffffe0 00000000000000c0 ffffffff818cab1d
 ffff88003ae8bd68 ffffffff81628db4 ffff88003ae8bd48 ffff88003b7f5550
 ffff880031a09408 ffff88003b7f5550 ffff88000012aa48 ffff88000012ab00
Call Trace:
 [<ffffffff81628db4>] unix_stream_sendmsg+0x2c4/0x470
 [<ffffffff81556f56>] sock_write_iter+0x146/0x160
 [<ffffffff811d9612>] new_sync_write+0x92/0xd0
 [<ffffffff811d9cd6>] vfs_write+0xd6/0x180
 [<ffffffff811da499>] SyS_write+0x59/0xd0
 [<ffffffff81651532>] system_call_fastpath+0x12/0x17
Code: 00 00 48 89 44 24 10 8b 87 c8 00 00 00 48 89 44 24 08 48 8b 87 d8 00
      00 00 48 c7 c7 30 db 91 81 48 89 04 24 31 c0 e8 4f a8 0e 00 <0f> 0b
      eb fe 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 48 83
RIP  [<ffffffff8155fbd1>] skb_put+0xa1/0xb0
RSP <ffff88003ae8bc68>
Kernel panic - not syncing: Fatal exception

Moreover, the possible minimum is 1, so we can get another kernel panic:
...
BUG: unable to handle kernel paging request at ffff88013caee5c0
IP: [<ffffffff815604cf>] __alloc_skb+0x12f/0x1f0
...

Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: delete now-unused 'one' variable]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 2d6dfb109bfbf3abd5f762173b1d73fd321dbe37)
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 net/core/sysctl_net_core.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index a600328..d0a07c2 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -17,7 +17,8 @@
 static int zero = 0;
 static int ushort_max = 65535;
 
-static int one = 1;
+static int min_sndbuf = SOCK_MIN_SNDBUF;
+static int min_rcvbuf = SOCK_MIN_RCVBUF;
 
 static struct ctl_table net_core_table[] = {
 #ifdef CONFIG_NET
@@ -29,7 +30,7 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.strategy	= sysctl_intvec,
-		.extra1		= &one,
+		.extra1		= &min_sndbuf,
 	},
 	{
 		.ctl_name	= NET_CORE_RMEM_MAX,
@@ -39,7 +40,7 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.strategy	= sysctl_intvec,
-		.extra1		= &one,
+		.extra1		= &min_rcvbuf,
 	},
 	{
 		.ctl_name	= NET_CORE_WMEM_DEFAULT,
@@ -49,7 +50,7 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.strategy	= sysctl_intvec,
-		.extra1		= &one,
+		.extra1		= &min_sndbuf,
 	},
 	{
 		.ctl_name	= NET_CORE_RMEM_DEFAULT,
@@ -59,7 +60,7 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
 		.strategy	= sysctl_intvec,
-		.extra1		= &one,
+		.extra1		= &min_rcvbuf,
 	},
 	{
 		.ctl_name	= NET_CORE_DEV_WEIGHT,
-- 
1.7.12.2.21.g234cd45.dirty