[tip: core/urgent] core/entry: Respect syscall number rewrites

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the core/urgent branch of tip:

Commit-ID:     d88d59b64ca35abae208e2781fdb45e69cbed56c
Gitweb:        https://git.kernel.org/tip/d88d59b64ca35abae208e2781fdb45e69cbed56c
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Wed, 19 Aug 2020 21:44:39 +02:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Fri, 21 Aug 2020 16:17:29 +02:00

core/entry: Respect syscall number rewrites

The transcript of the x86 entry code to the generic version failed to
reload the syscall number from ptregs after ptrace and seccomp have run,
which both can modify the syscall number in ptregs. It returns the original
syscall number instead which is obviously not the right thing to do.

Reload the syscall number to fix that.

Fixes: 142781e108b1 ("entry: Provide generic syscall entry functionality")
Reported-by: Kyle Huey <me@xxxxxxxxxxxx> 
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Kyle Huey <me@xxxxxxxxxxxx> 
Tested-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/87blj6ifo8.fsf@xxxxxxxxxxxxxxxxxxxxxxx

---
 kernel/entry/common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 9852e0d..fcae019 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -65,7 +65,8 @@ static long syscall_trace_enter(struct pt_regs *regs, long syscall,
 
 	syscall_enter_audit(regs, syscall);
 
-	return ret ? : syscall;
+	/* The above might have changed the syscall number */
+	return ret ? : syscall_get_nr(current, regs);
 }
 
 noinstr long syscall_enter_from_user_mode(struct pt_regs *regs, long syscall)