[PATCH 3.2 202/221] net: sysctl_net_core: check SNDBUF and RCVBUF for min length

Ben Hutchings
2015-05-05T02:30:24Z

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>
---
net/core/sysctl_net_core.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -21,8 +21,8 @@

static int zero = 0;
static int ushort_max = USHRT_MAX;
-
-static int one = 1;
+static int min_sndbuf = SOCK_MIN_SNDBUF;
+static int min_rcvbuf = SOCK_MIN_RCVBUF;

#ifdef CONFIG_RPS
static int rps_sock_flow_sysctl(ctl_table *table, int write,
@@ -92,7 +92,7 @@ static struct ctl_table net_core_table[]
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
- .extra1 = &one,
+ .extra1 = &min_sndbuf,
},
{
.procname = "rmem_max",
@@ -100,7 +100,7 @@ static struct ctl_table net_core_table[]
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
- .extra1 = &one,
+ .extra1 = &min_rcvbuf,
},
{
.procname = "wmem_default",
@@ -108,7 +108,7 @@ static struct ctl_table net_core_table[]
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
- .extra1 = &one,
+ .extra1 = &min_sndbuf,
},
{
.procname = "rmem_default",
@@ -116,7 +116,7 @@ static struct ctl_table net_core_table[]
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
- .extra1 = &one,
+ .extra1 = &min_rcvbuf,
},
{
.procname = "dev_weight",