hulk inclusion category: bugfix bugzilla: 13690 CVE: CVE-2019-19462

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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.

https://lore.kernel.org/lkml/20191219121256.26480-1-dja%40axtens.net/ Fixes: 017c59c042d0 ("relay: Use per CPU constructs for the relay channel buffer pointers") Signed-off-by: Yang Yingliang yangyingliang@huawei.com Reviewed-by: Hanjun Guo guohanjun@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- kernel/relay.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/kernel/relay.c b/kernel/relay.c index 9e0f523..078f733 100644 --- a/kernel/relay.c +++ b/kernel/relay.c @@ -581,6 +581,10 @@ 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;