[100/127] kernel/relay.c: handle alloc_percpu returning NULL in relay_open

Commit Message

Andrew Morton June 4, 2020, 11:51 p.m. UTC

From: Daniel Axtens <[e-mail]>
Subject: kernel/relay.c: handle alloc_percpu returning NULL in relay_open

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.

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 017c59c042d0 ("relay: Use per CPU constructs for the relay channel buffer pointers")
Signed-off-by: Daniel Axtens <[e-mail]>
Reviewed-by: Michael Ellerman <[e-mail]>
Reviewed-by: Andrew Donnellan <[e-mail]>
Acked-by: David Rientjes <[e-mail]>
Reported-by: [e-mail]
Reported-by: [e-mail]
Reported-by: [e-mail]
Reported-by: [e-mail]
Cc: Akash Goel <[e-mail]>
Cc: Andrew Donnellan <[e-mail]>
Cc: Guenter Roeck <[e-mail]>
Cc: Salvatore Bonaccorso <[e-mail]>
Cc: <[e-mail]>	[4.10+]
Signed-off-by: Andrew Morton <[e-mail]>
---

 kernel/relay.c |    5 +++++
 1 file changed, 5 insertions(+)

Patch

--- a/kernel/relay.c~relay-handle-alloc_percpu-returning-null-in-relay_open
+++ a/kernel/relay.c
@@ -581,6 +581,11 @@  struct rchan *relay_open(const char *bas
 		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;