ARC: entry: fix off-by-one error in syscall number validation

commit 3433adc8bd09fc9f29b8baddf33b4ecd1ecd2cdc upstream.

We have NR_syscall syscalls from [0 .. NR_syscall-1].
However the check for invalid syscall number is "> NR_syscall" as
opposed to >=. This off-by-one error erronesously allows "NR_syscall"
to be treated as valid syscall causeing out-of-bounds access into
syscall-call table ensuing a crash (holes within syscall table have a
invalid-entry handler but this is beyond the array implementing the
table).

This problem showed up on v5.6 kernel when testing glibc 2.33 (v5.10
kernel capable, includng faccessat2 syscall 439). The v5.6 kernel has
NR_syscalls=439 (0 to 438). Due to the bug, 439 passed by glibc was
not handled as -ENOSYS but processed leading to a crash.

Link: https://github.com/foss-for-synopsys-dwc-arc-processors/linux/issues/48
Reported-by: Shahab Vahedi <shahab@synopsys.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index db1eee5fe502432900c5c306c608ab33bf03dd37..6da48c1e3475727b4ad6870b9fe32bf71003338b 100644 (file)
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -181,7 +181,7 @@ tracesys:
 
        ; Do the Sys Call as we normally would.
        ; Validate the Sys Call number
-       cmp     r8,  NR_syscalls
+       cmp     r8,  NR_syscalls - 1
        mov.hi  r0, -ENOSYS
        bhi     tracesys_exit
 
@@ -264,7 +264,7 @@ ENTRY(EV_Trap)
        ;============ Normal syscall case
 
        ; syscall num shd not exceed the total system calls avail
-       cmp     r8,  NR_syscalls
+       cmp     r8,  NR_syscalls - 1
        mov.hi  r0, -ENOSYS
        bhi     ret_from_system_call