From: Daniel Axtens <dja@axtens.net>
Subject: [PATCH v2] relay: handle alloc_percpu returning NULL in relay_open
Date: Thu, 19 Dec 2019 23:12:56 +1100
Message-id: <20191219121256.26480-1-dja@axtens.net>
Patch-mainline: Submitted, LKML
References: CVE-2019-19462 bsc#1158265
alloc_percpu() may return NULL, which means chan->buf may be set to
NULL. In that case, when we do *per_cpu_ptr(chan->buf, ...), we
dereference an invalid pointer:
Bug: Unable to handle kernel data access at 0x7dae0000
Faulting instruction address: 0xc0000000003f3fec
...
NIP [c0000000003f3fec] relay_open+0x29c/0x600
LR [c0000000003f3fc0] relay_open+0x270/0x600
Call Trace:
[c000000054353a70] [c0000000003f3fb4] relay_open+0x264/0x600 (unreliable)
[c000000054353b00] [c000000000451764] __blk_trace_setup+0x254/0x600
[c000000054353bb0] [c000000000451b78] blk_trace_setup+0x68/0xa0
[c000000054353c10] [c0000000010da77c] sg_ioctl+0x7bc/0x2e80
[c000000054353cd0] [c000000000758cbc] do_vfs_ioctl+0x13c/0x1300
[c000000054353d90] [c000000000759f14] ksys_ioctl+0x94/0x130
[c000000054353de0] [c000000000759ff8] sys_ioctl+0x48/0xb0
[c000000054353e20] [c00000000000bcd0] system_call+0x5c/0x68
Check if alloc_percpu returns NULL.
This was found by syzkaller both on x86 and powerpc, and the reproducer
it found on powerpc is capable of hitting the issue as an unprivileged
user.
Fixes: 017c59c042d0 ("relay: Use per CPU constructs for the relay channel buffer pointers")
Reported-by: syzbot+1e925b4b836afe85a1c6@syzkaller-ppc64.appspotmail.com
Reported-by: syzbot+587b2421926808309d21@syzkaller-ppc64.appspotmail.com
Reported-by: syzbot+58320b7171734bf79d26@syzkaller.appspotmail.com
Reported-by: syzbot+d6074fb08bdb2e010520@syzkaller.appspotmail.com
Cc: Akash Goel <akash.goel@intel.com>
Cc: Andrew Donnellan <ajd@linux.ibm.com> # syzkaller-ppc64
Reviewed-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Cc: stable@vger.kernel.org # v4.10+
Signed-off-by: Daniel Axtens <dja@axtens.net>
Acked-by: Takashi Iwai <tiwai@suse.de>
---
kernel/relay.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/relay.c b/kernel/relay.c
index ade14fb7ce2e..4b760ec16342 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -581,6 +581,11 @@ struct rchan *relay_open(const char *base_filename,
return NULL;
chan->buf = alloc_percpu(struct rchan_buf *);
+ if (!chan->buf) {
+ kfree(chan);
+ return NULL;
+ }
+
chan->version = RELAYFS_CHANNEL_VERSION;
chan->n_subbufs = n_subbufs;
chan->subbuf_size = subbuf_size;
--
2.20.1