igmp: fix memory leak in igmpv3_del_delrec() [Linux 4.9.187]

This Linux kernel change "igmp: fix memory leak in igmpv3_del_delrec()" is included in the Linux 4.9.187 release. This change is authored by Eric Dumazet <edumazet [at] google.com> on Thu Jun 27 01:27:01 2019 -0700. The commit for this change in Linux stable tree is 84d0edf (patch) which is from upstream commit e5b1c6c. The same Linux upstream change may have been applied to various maintained Linux releases and you can find all Linux releases containing changes from upstream e5b1c6c.

igmp: fix memory leak in igmpv3_del_delrec()

[ Upstream commit e5b1c6c6277d5a283290a8c033c72544746f9b5b ]

im->tomb and/or im->sources might not be NULL, but we
currently overwrite their values blindly.

Using swap() will make sure the following call to kfree_pmc(pmc)
will properly free the psf structures.

Tested with the C repro provided by syzbot, which basically does :

 socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
 setsockopt(3, SOL_IP, IP_ADD_MEMBERSHIP, "\340\0\0\2\177\0\0\1\0\0\0\0", 12) = 0
 ioctl(3, SIOCSIFFLAGS, {ifr_name="lo", ifr_flags=0}) = 0
 setsockopt(3, SOL_IP, IP_MSFILTER, "\340\0\0\2\177\0\0\1\1\0\0\0\1\0\0\0\377\377\377\377", 20) = 0
 ioctl(3, SIOCSIFFLAGS, {ifr_name="lo", ifr_flags=IFF_UP}) = 0
 exit_group(0)                    = ?

BUG: memory leak
unreferenced object 0xffff88811450f140 (size 64):
  comm "softirq", pid 0, jiffies 4294942448 (age 32.070s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 ff ff ff ff 00 00 00 00  ................
    00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
  backtrace:
    [<00000000c7bad083>] kmemleak_alloc_recursive include/linux/kmemleak.h:43 [inline]
    [<00000000c7bad083>] slab_post_alloc_hook mm/slab.h:439 [inline]
    [<00000000c7bad083>] slab_alloc mm/slab.c:3326 [inline]
    [<00000000c7bad083>] kmem_cache_alloc_trace+0x13d/0x280 mm/slab.c:3553
    [<000000009acc4151>] kmalloc include/linux/slab.h:547 [inline]
    [<000000009acc4151>] kzalloc include/linux/slab.h:742 [inline]
    [<000000009acc4151>] ip_mc_add1_src net/ipv4/igmp.c:1976 [inline]
    [<000000009acc4151>] ip_mc_add_src+0x36b/0x400 net/ipv4/igmp.c:2100
    [<000000004ac14566>] ip_mc_msfilter+0x22d/0x310 net/ipv4/igmp.c:2484
    [<0000000052d8f995>] do_ip_setsockopt.isra.0+0x1795/0x1930 net/ipv4/ip_sockglue.c:959
    [<000000004ee1e21f>] ip_setsockopt+0x3b/0xb0 net/ipv4/ip_sockglue.c:1248
    [<0000000066cdfe74>] udp_setsockopt+0x4e/0x90 net/ipv4/udp.c:2618
    [<000000009383a786>] sock_common_setsockopt+0x38/0x50 net/core/sock.c:3126
    [<00000000d8ac0c94>] __sys_setsockopt+0x98/0x120 net/socket.c:2072
    [<000000001b1e9666>] __do_sys_setsockopt net/socket.c:2083 [inline]
    [<000000001b1e9666>] __se_sys_setsockopt net/socket.c:2080 [inline]
    [<000000001b1e9666>] __x64_sys_setsockopt+0x26/0x30 net/socket.c:2080
    [<00000000420d395e>] do_syscall_64+0x76/0x1a0 arch/x86/entry/common.c:301
    [<000000007fd83a4b>] entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fixes: 24803f38a5c0 ("igmp: do not remove igmp souce list info when set link down")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Hangbin Liu <liuhangbin@gmail.com>
Reported-by: syzbot+6ca1abd0db68b5173a4f@syzkaller.appspotmail.com
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 net/ipv4/igmp.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 780dc6f..02c1736 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1212,12 +1212,8 @@ static void igmpv3_del_delrec(struct in_device *in_dev, struct ip_mc_list *im)
        im->interface = pmc->interface;
        im->crcount = in_dev->mr_qrv ?: net->ipv4.sysctl_igmp_qrv;
        if (im->sfmode == MCAST_INCLUDE) {
-           im->tomb = pmc->tomb;
-           pmc->tomb = NULL;
-
-           im->sources = pmc->sources;
-           pmc->sources = NULL;
-
+           swap(im->tomb, pmc->tomb);
+           swap(im->sources, pmc->sources);
            for (psf = im->sources; psf; psf = psf->sf_next)
                psf->sf_crcount = im->crcount;
        }

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