From: Daniel Axtens dja@axtens.net
commit 54e200ab40fc14c863bcc80a51e20b7906608fce upstream.
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 relay_open+0x29c/0x600 LR relay_open+0x270/0x600 Call Trace: relay_open+0x264/0x600 (unreliable) __blk_trace_setup+0x254/0x600 blk_trace_setup+0x68/0xa0 sg_ioctl+0x7bc/0x2e80 do_vfs_ioctl+0x13c/0x1300 ksys_ioctl+0x94/0x130 sys_ioctl+0x48/0xb0 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 Signed-off-by: Daniel Axtens dja@axtens.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Reviewed-by: Michael Ellerman mpe@ellerman.id.au Reviewed-by: Andrew Donnellan ajd@linux.ibm.com Acked-by: David Rientjes rientjes@google.com Cc: Akash Goel akash.goel@intel.com Cc: Andrew Donnellan ajd@linux.ibm.com Cc: Guenter Roeck linux@roeck-us.net Cc: Salvatore Bonaccorso carnil@debian.org Cc: stable@vger.kernel.org [4.10+] Link: http://lkml.kernel.org/r/20191219121256.26480-1-dja@axtens.net Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/relay.c | 5 +++++ 1 file changed, 5 insertions(+)
--- a/kernel/relay.c +++ b/kernel/relay.c @@ -580,6 +580,11 @@ 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;