4.20-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet edumazet@google.com
commit 63530aba7826a0f8e129874df9c4d264f9db3f9e upstream.
syzbot found that ax25 routes where not properly protected against concurrent use [1].
In this particular report the bug happened while copying ax25->digipeat.
Fix this problem by making sure we call ax25_get_route() while ax25_route_lock is held, so that no modification could happen while using the route.
The current two ax25_get_route() callers do not sleep, so this change should be fine.
Once we do that, ax25_get_route() no longer needs to grab a reference on the found route.
[1] ax25_connect(): syz-executor0 uses autobind, please contact jreuter@yaina.de BUG: KASAN: use-after-free in memcpy include/linux/string.h:352 [inline] BUG: KASAN: use-after-free in kmemdup+0x42/0x60 mm/util.c:113 Read of size 66 at addr ffff888066641a80 by task syz-executor2/531
ax25_connect(): syz-executor0 uses autobind, please contact jreuter@yaina.de CPU: 1 PID: 531 Comm: syz-executor2 Not tainted 5.0.0-rc2+ #10 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x1db/0x2d0 lib/dump_stack.c:113 print_address_description.cold+0x7c/0x20d mm/kasan/report.c:187 kasan_report.cold+0x1b/0x40 mm/kasan/report.c:317 check_memory_region_inline mm/kasan/generic.c:185 [inline] check_memory_region+0x123/0x190 mm/kasan/generic.c:191 memcpy+0x24/0x50 mm/kasan/common.c:130 memcpy include/linux/string.h:352 [inline] kmemdup+0x42/0x60 mm/util.c:113 kmemdup include/linux/string.h:425 [inline] ax25_rt_autobind+0x25d/0x750 net/ax25/ax25_route.c:424 ax25_connect.cold+0x30/0xa4 net/ax25/af_ax25.c:1224 __sys_connect+0x357/0x490 net/socket.c:1664 __do_sys_connect net/socket.c:1675 [inline] __se_sys_connect net/socket.c:1672 [inline] __x64_sys_connect+0x73/0xb0 net/socket.c:1672 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe RIP: 0033:0x458099 Code: 6d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 RSP: 002b:00007f870ee22c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002a RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000458099 RDX: 0000000000000048 RSI: 0000000020000080 RDI: 0000000000000005 RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000 ax25_connect(): syz-executor4 uses autobind, please contact jreuter@yaina.de R10: 0000000000000000 R11: 0000000000000246 R12: 00007f870ee236d4 R13: 00000000004be48e R14: 00000000004ce9a8 R15: 00000000ffffffff
Allocated by task 526: save_stack+0x45/0xd0 mm/kasan/common.c:73 set_track mm/kasan/common.c:85 [inline] __kasan_kmalloc mm/kasan/common.c:496 [inline] __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:469 kasan_kmalloc+0x9/0x10 mm/kasan/common.c:504 ax25_connect(): syz-executor5 uses autobind, please contact jreuter@yaina.de kmem_cache_alloc_trace+0x151/0x760 mm/slab.c:3609 kmalloc include/linux/slab.h:545 [inline] ax25_rt_add net/ax25/ax25_route.c:95 [inline] ax25_rt_ioctl+0x3b9/0x1270 net/ax25/ax25_route.c:233 ax25_ioctl+0x322/0x10b0 net/ax25/af_ax25.c:1763 sock_do_ioctl+0xe2/0x400 net/socket.c:950 sock_ioctl+0x32f/0x6c0 net/socket.c:1074 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0x107b/0x17d0 fs/ioctl.c:696 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe
ax25_connect(): syz-executor5 uses autobind, please contact jreuter@yaina.de Freed by task 550: save_stack+0x45/0xd0 mm/kasan/common.c:73 set_track mm/kasan/common.c:85 [inline] __kasan_slab_free+0x102/0x150 mm/kasan/common.c:458 kasan_slab_free+0xe/0x10 mm/kasan/common.c:466 __cache_free mm/slab.c:3487 [inline] kfree+0xcf/0x230 mm/slab.c:3806 ax25_rt_add net/ax25/ax25_route.c:92 [inline] ax25_rt_ioctl+0x304/0x1270 net/ax25/ax25_route.c:233 ax25_ioctl+0x322/0x10b0 net/ax25/af_ax25.c:1763 sock_do_ioctl+0xe2/0x400 net/socket.c:950 sock_ioctl+0x32f/0x6c0 net/socket.c:1074 vfs_ioctl fs/ioctl.c:46 [inline] file_ioctl fs/ioctl.c:509 [inline] do_vfs_ioctl+0x107b/0x17d0 fs/ioctl.c:696 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713 __do_sys_ioctl fs/ioctl.c:720 [inline] __se_sys_ioctl fs/ioctl.c:718 [inline] __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290 entry_SYSCALL_64_after_hwframe+0x49/0xbe
The buggy address belongs to the object at ffff888066641a80 which belongs to the cache kmalloc-96 of size 96 The buggy address is located 0 bytes inside of 96-byte region [ffff888066641a80, ffff888066641ae0) The buggy address belongs to the page: page:ffffea0001999040 count:1 mapcount:0 mapping:ffff88812c3f04c0 index:0x0 flags: 0x1fffc0000000200(slab) ax25_connect(): syz-executor4 uses autobind, please contact jreuter@yaina.de raw: 01fffc0000000200 ffffea0001817948 ffffea0002341dc8 ffff88812c3f04c0 raw: 0000000000000000 ffff888066641000 0000000100000020 0000000000000000 page dumped because: kasan: bad access detected
Memory state around the buggy address: ffff888066641980: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc ffff888066641a00: 00 00 00 00 00 00 00 00 02 fc fc fc fc fc fc fc
ffff888066641a80: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^ ffff888066641b00: fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc ffff888066641b80: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
Signed-off-by: Eric Dumazet edumazet@google.com Cc: Ralf Baechle ralf@linux-mips.org Reported-by: syzbot syzkaller@googlegroups.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- include/net/ax25.h | 12 ++++++++++++ net/ax25/ax25_ip.c | 4 ++-- net/ax25/ax25_route.c | 19 ++++++++----------- 3 files changed, 22 insertions(+), 13 deletions(-)
--- a/include/net/ax25.h +++ b/include/net/ax25.h @@ -201,6 +201,18 @@ static inline void ax25_hold_route(ax25_
void __ax25_put_route(ax25_route *ax25_rt);
+extern rwlock_t ax25_route_lock; + +static inline void ax25_route_lock_use(void) +{ + read_lock(&ax25_route_lock); +} + +static inline void ax25_route_lock_unuse(void) +{ + read_unlock(&ax25_route_lock); +} + static inline void ax25_put_route(ax25_route *ax25_rt) { if (refcount_dec_and_test(&ax25_rt->refcount)) --- a/net/ax25/ax25_ip.c +++ b/net/ax25/ax25_ip.c @@ -114,6 +114,7 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff dst = (ax25_address *)(bp + 1); src = (ax25_address *)(bp + 8);
+ ax25_route_lock_use(); route = ax25_get_route(dst, NULL); if (route) { digipeat = route->digipeat; @@ -206,9 +207,8 @@ netdev_tx_t ax25_ip_xmit(struct sk_buff ax25_queue_xmit(skb, dev);
put: - if (route) - ax25_put_route(route);
+ ax25_route_lock_unuse(); return NETDEV_TX_OK; }
--- a/net/ax25/ax25_route.c +++ b/net/ax25/ax25_route.c @@ -40,7 +40,7 @@ #include <linux/export.h>
static ax25_route *ax25_route_list; -static DEFINE_RWLOCK(ax25_route_lock); +DEFINE_RWLOCK(ax25_route_lock);
void ax25_rt_device_down(struct net_device *dev) { @@ -335,6 +335,7 @@ const struct seq_operations ax25_rt_seqo * Find AX.25 route * * Only routes with a reference count of zero can be destroyed. + * Must be called with ax25_route_lock read locked. */ ax25_route *ax25_get_route(ax25_address *addr, struct net_device *dev) { @@ -342,7 +343,6 @@ ax25_route *ax25_get_route(ax25_address ax25_route *ax25_def_rt = NULL; ax25_route *ax25_rt;
- read_lock(&ax25_route_lock); /* * Bind to the physical interface we heard them on, or the default * route if none is found; @@ -365,11 +365,6 @@ ax25_route *ax25_get_route(ax25_address if (ax25_spe_rt != NULL) ax25_rt = ax25_spe_rt;
- if (ax25_rt != NULL) - ax25_hold_route(ax25_rt); - - read_unlock(&ax25_route_lock); - return ax25_rt; }
@@ -400,9 +395,12 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25 ax25_route *ax25_rt; int err = 0;
- if ((ax25_rt = ax25_get_route(addr, NULL)) == NULL) + ax25_route_lock_use(); + ax25_rt = ax25_get_route(addr, NULL); + if (!ax25_rt) { + ax25_route_lock_unuse(); return -EHOSTUNREACH; - + } if ((ax25->ax25_dev = ax25_dev_ax25dev(ax25_rt->dev)) == NULL) { err = -EHOSTUNREACH; goto put; @@ -437,8 +435,7 @@ int ax25_rt_autobind(ax25_cb *ax25, ax25 }
put: - ax25_put_route(ax25_rt); - + ax25_route_lock_unuse(); return err; }