[PATCH 4.2 016/110] powerpc/rtas: Validate rtas.entry before calling enter_rtas()

[Greg Kroah-Hartman]

4.2-stable review patch.  If anyone has any objections, please let me know.

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

From: Vasant Hegde <hegdevasant@xxxxxxxxxxxxxxxxxx>

commit 8832317f662c06f5c06e638f57bfe89a71c9b266 upstream.

Currently we do not validate rtas.entry before calling enter_rtas(). This
leads to a kernel oops when user space calls rtas system call on a powernv
platform (see below). This patch adds code to validate rtas.entry before
making enter_rtas() call.

  Oops: Exception in kernel mode, sig: 4 [#1]
  SMP NR_CPUS=1024 NUMA PowerNV
  task: c000000004294b80 ti: c0000007e1a78000 task.ti: c0000007e1a78000
  NIP: 0000000000000000 LR: 0000000000009c14 CTR: c000000000423140
  REGS: c0000007e1a7b920 TRAP: 0e40   Not tainted  (3.18.17-340.el7_1.pkvm3_1_0.2400.1.ppc64le)
  MSR: 1000000000081000 <HV,ME>  CR: 00000000  XER: 00000000
  CFAR: c000000000009c0c SOFTE: 0
  NIP [0000000000000000]           (null)
  LR [0000000000009c14] 0x9c14
  Call Trace:
  [c0000007e1a7bba0] [c00000000041a7f4] avc_has_perm_noaudit+0x54/0x110 (unreliable)
  [c0000007e1a7bd80] [c00000000002ddc0] ppc_rtas+0x150/0x2d0
  [c0000007e1a7be30] [c000000000009358] syscall_exit+0x0/0x98

Fixes: 55190f88789a ("powerpc: Add skeleton PowerNV platform")
Reported-by: NAGESWARA R. SASTRY <nasastry@xxxxxxxxxx>
Signed-off-by: Vasant Hegde <hegdevasant@xxxxxxxxxxxxxxxxxx>
[mpe: Reword change log, trim oops, and add stable + fixes]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/powerpc/kernel/rtas.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -1041,6 +1041,9 @@ asmlinkage int ppc_rtas(struct rtas_args
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	if (!rtas.entry)
+		return -EINVAL;
+
 	if (copy_from_user(&args, uargs, 3 * sizeof(u32)) != 0)
 		return -EFAULT;
 


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