linux-kernel - [PATCH v2 1/3] um/ptrace: Fix the syscall_trace

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Date:	Mon,  1 Aug 2016 23:01:55 +0200
From:	Mickaël Salaün <mic@...ikod.net>
To:	linux-kernel@...r.kernel.org
Cc:	Mickaël Salaün <mic@...ikod.net>,
	Kees Cook <keescook@...omium.org>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	James Morris <jmorris@...ei.org>,
	Olof Johansson <olof@...om.net>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-security-module@...r.kernel.org
Subject: [PATCH v2 1/3] um/ptrace: Fix the syscall_trace_leave call

Keep the same semantic as before the commit 26703c636c1f: deallocate
audit context and fake a proper syscall exit.

This fix a kernel panic triggered by the seccomp_bpf test:
> [ RUN      ] global.ERRNO_valid
> BUG: failure at kernel/auditsc.c:1504/__audit_syscall_entry()!
> Kernel panic - not syncing: BUG!

Fixes: 26703c636c1f ("um/ptrace: run seccomp after ptrace")

Signed-off-by: Mickaël Salaün <mic@...ikod.net>
Acked-by: Kees Cook <keescook@...omium.org>
Cc: Jeff Dike <jdike@...toit.com>
Cc: Richard Weinberger <richard@....at>
Cc: James Morris <jmorris@...ei.org>
Cc: user-mode-linux-devel@...ts.sourceforge.net
---
 arch/um/kernel/skas/syscall.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/um/kernel/skas/syscall.c b/arch/um/kernel/skas/syscall.c
index ef4b8f949b51..0728fee94398 100644
--- a/arch/um/kernel/skas/syscall.c
+++ b/arch/um/kernel/skas/syscall.c
@@ -21,11 +21,11 @@ void handle_syscall(struct uml_pt_regs *r)
 	PT_REGS_SET_SYSCALL_RETURN(regs, -ENOSYS);
 
 	if (syscall_trace_enter(regs))
-		return;
+		goto out;
 
 	/* Do the seccomp check after ptrace; failures should be fast. */
 	if (secure_computing(NULL) == -1)
-		return;
+		goto out;
 
 	/* Update the syscall number after orig_ax has potentially been updated
 	 * with ptrace.
@@ -37,5 +37,6 @@ void handle_syscall(struct uml_pt_regs *r)
 		PT_REGS_SET_SYSCALL_RETURN(regs,
 				EXECUTE_SYSCALL(syscall, regs));
 
+out:
 	syscall_trace_leave(regs);
 }
-- 
2.8.1