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Subject[PATCH 4.4 012/124] nfsd: fix potential use-after-free in nfsd4_decode_getdeviceinfo
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Scott Mayhew <smayhew@redhat.com>

[ Upstream commit 3171822fdcdd6e6d536047c425af6dc7a92dc585 ]

When running a fuzz tester against a KASAN-enabled kernel, the following
splat periodically occurs.

The problem occurs when the test sends a GETDEVICEINFO request with a
malformed xdr array (size but no data) for gdia_notify_types and the
array size is > 0x3fffffff, which results in an overflow in the value of
nbytes which is passed to read_buf().

If the array size is 0x40000000, 0x80000000, or 0xc0000000, then after
the overflow occurs, the value of nbytes 0, and when that happens the
pointer returned by read_buf() points to the end of the xdr data (i.e.
argp->end) when really it should be returning NULL.

Fix this by returning NFS4ERR_BAD_XDR if the array size is > 1000 (this
value is arbitrary, but it's the same threshold used by
nfsd4_decode_bitmap()... in could really be any value >= 1 since it's
expected to get at most a single bitmap in gdia_notify_types).

[ 119.256854] ==================================================================
[ 119.257611] BUG: KASAN: use-after-free in nfsd4_decode_getdeviceinfo+0x5a4/0x5b0 [nfsd]
[ 119.258422] Read of size 4 at addr ffff880113ada000 by task nfsd/538

[ 119.259146] CPU: 0 PID: 538 Comm: nfsd Not tainted 4.17.0+ #1
[ 119.259662] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc25 04/01/2014
[ 119.261202] Call Trace:
[ 119.262265] dump_stack+0x71/0xab
[ 119.263371] print_address_description+0x6a/0x270
[ 119.264609] kasan_report+0x258/0x380
[ 119.265854] ? nfsd4_decode_getdeviceinfo+0x5a4/0x5b0 [nfsd]
[ 119.267291] nfsd4_decode_getdeviceinfo+0x5a4/0x5b0 [nfsd]
[ 119.268549] ? nfs4svc_decode_compoundargs+0xa5b/0x13c0 [nfsd]
[ 119.269873] ? nfsd4_decode_sequence+0x490/0x490 [nfsd]
[ 119.271095] nfs4svc_decode_compoundargs+0xa5b/0x13c0 [nfsd]
[ 119.272393] ? nfsd4_release_compoundargs+0x1b0/0x1b0 [nfsd]
[ 119.273658] nfsd_dispatch+0x183/0x850 [nfsd]
[ 119.274918] svc_process+0x161c/0x31a0 [sunrpc]
[ 119.276172] ? svc_printk+0x190/0x190 [sunrpc]
[ 119.277386] ? svc_xprt_release+0x451/0x680 [sunrpc]
[ 119.278622] nfsd+0x2b9/0x430 [nfsd]
[ 119.279771] ? nfsd_destroy+0x1c0/0x1c0 [nfsd]
[ 119.281157] kthread+0x2db/0x390
[ 119.282347] ? kthread_create_worker_on_cpu+0xc0/0xc0
[ 119.283756] ret_from_fork+0x35/0x40

[ 119.286041] Allocated by task 436:
[ 119.287525] kasan_kmalloc+0xa0/0xd0
[ 119.288685] kmem_cache_alloc+0xe9/0x1f0
[ 119.289900] get_empty_filp+0x7b/0x410
[ 119.291037] path_openat+0xca/0x4220
[ 119.292242] do_filp_open+0x182/0x280
[ 119.293411] do_sys_open+0x216/0x360
[ 119.294555] do_syscall_64+0xa0/0x2f0
[ 119.295721] entry_SYSCALL_64_after_hwframe+0x44/0xa9

[ 119.298068] Freed by task 436:
[ 119.299271] __kasan_slab_free+0x130/0x180
[ 119.300557] kmem_cache_free+0x78/0x210
[ 119.301823] rcu_process_callbacks+0x35b/0xbd0
[ 119.303162] __do_softirq+0x192/0x5ea

[ 119.305443] The buggy address belongs to the object at ffff880113ada000
which belongs to the cache filp of size 256
[ 119.308556] The buggy address is located 0 bytes inside of
256-byte region [ffff880113ada000, ffff880113ada100)
[ 119.311376] The buggy address belongs to the page:
[ 119.312728] page:ffffea00044eb680 count:1 mapcount:0 mapping:0000000000000000 index:0xffff880113ada780
[ 119.314428] flags: 0x17ffe000000100(slab)
[ 119.315740] raw: 0017ffe000000100 0000000000000000 ffff880113ada780 00000001000c0001
[ 119.317379] raw: ffffea0004553c60 ffffea00045c11e0 ffff88011b167e00 0000000000000000
[ 119.319050] page dumped because: kasan: bad access detected

[ 119.321652] Memory state around the buggy address:
[ 119.322993] ffff880113ad9f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 119.324515] ffff880113ad9f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[ 119.326087] >ffff880113ada000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 119.327547] ^
[ 119.328730] ffff880113ada080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 119.330218] ffff880113ada100: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
[ 119.331740] ==================================================================

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/nfsd/nfs4xdr.c | 2 ++
1 file changed, 2 insertions(+)

--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -1538,6 +1538,8 @@ nfsd4_decode_getdeviceinfo(struct nfsd4_
gdev->gd_maxcount = be32_to_cpup(p++);
num = be32_to_cpup(p++);
if (num) {
+ if (num > 1000)
+ goto xdr_error;
READ_BUF(4 * num);
gdev->gd_notify_types = be32_to_cpup(p++);
for (i = 1; i < num; i++) {

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